planet.freedesktop.org
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| July 21, 2017 | |
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I planned on writing about the Present extension this week, but I’ll postpone this since I’m currently strongly absorbed into finding the last rough edges of a first patch I can show off. I then hope to get some feedback on this from other developers in the xorg-devel mailing list.
Another reason is that I stalled my work on the Present extension for now and try to get first my Xwayland code working. My mentor Daniel recommended that to me since the approach I pursued in my work on Present might be more difficult than I first assessed. At least it is something similar to what other way more experienced developers than myself tried in the past and weren’t able to do according to Daniel. My idea was to make Present flip per CRTC only, but this would clash with Pixmaps being linked to the whole screen only. There are no Pixmaps only for CRTCs in X.
On the other hand when accepting the restriction of only being able to flip one window at a time my code already works quite good. The flipping is smooth and at least in a short test also improved the frame rate. But the main problem I had and still to some degree have, is that stopping the flipping can fail. The reason seems to be that the Present extension sets always the Screen Pixmap on flips. But when I test my work with KWin, it drives Xwayland in rootless mode, i.e. without a Screen Pixmap and only the Window Pixmaps. I’m currently looking into how to circumvent this in Xwayland. I think it’s possible, but I need to look very carefully on how to change the process in order to not forget necessary cleanups on the flipped Pixmaps. I hope though that I’m able to solve these issues already this weekend and then get some feedback on the xorg-devel mailing list.
As always you can find my latest work on my working branch on GitHub.
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| July 20, 2017 | |
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Since the last post a lot work has gone into upstreaming and stabilizing the etnaviv on Android ecosystem. This has involved Android, kernel and Mesa changes. Many of which are available upstream now. A How-To for getting you up and running on an iMX6 dev board is available here.
Modifiers support has been accepted into Mesa, GBM and gbm_gralloc. Modifiers were mentioned in a previous post.
Patches enabling the etnaviv Mesa driver being built for Android have now landed upstream.
A number for small stability issues present while running Android on i.MX6 hardware have now been fixed, and the platform is now relatively stable.
We have a decent understanding that the …
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| July 17, 2017 | |
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The great folks at kinvolk have uploaded a video of my casync presentation at their offices last week.
The slides are available as well.
Enjoy!
This week’s VC5 progress primarily involved rewriting the CLIF-style debug dumps using Intel’s gen_decode.c code. Instead of code-generating a bunch of C functions that print out a struct’s contents, I now have a little bit of C code that parses a compressed version of the XML at runtime to pick apart the struct and dump it. I’ve implemented this on VC4 and VC5, and started the Android build debugging process for it.
I also finished fixing the regressions from my VC5 QIR redesign. We now operate on just QPU instructions with sideband information for register allocation, instead of a higher-level IR (that’s what NIR is for).
For Raspbian performance, I’ve been talking with keithp and others about my window-dragging performance issue. My current plan is to implement a little GL extension that gives glBlitFramebuffer() defined behavior for 1:1 overlapping copies, and then use that from X11 to avoid the temporary. That should cut the cost of the window movement in half (not counting the cost of the drawing caused by the expose events).
On the KMS front, I’ve fixed a regression in dual-display support from my previous tiling work. In the process, I’ve also written a fix for panning, which was broken even before the tiling work. I’ve pushed a fix from Boris for a warning on CRTC enable. I’ve also worked on handling the review feedback from the last DSI series, and started on review of Hans’s VC4 CEC support.
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| July 14, 2017 | |
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I provided in the past few weeks some general information about my project and hopefully helpful documentation for the multiple components I’m working with, but I have not yet talked about the work I’m doing on the code itself. Let’s change this today.
You can find my work branch on GitHub. It’s basically just a personal repository so I can sync my work between my devices, so be warned: The commits are messy as nothing is cleaned up and debug lines as well as temporary TODOs are all over the place. And to be honest up until yesterday my changes didn’t accumulate to much. For some reason no picture was displayed in my two test applications, which are Neverball and VLC.
Then on the weekend suddenly the KWin Wayland session wouldn’t even launch anymore. Well, at least this issue I was able to fix pretty quickly. But there was still no picture, it seemed the presenting just halted after the first buffer was sent to KWin and without any further messages. Neither the Xwayland server nor the client were unresponsive though. Only today I finally could solve the problem thanks to Daniel’s help. The reason for the halt was that I waited on a frame callback from KWin in order to present the next frame. But this never arrived since I hadn’t set any damage in the previous frame and KWin then wouldn’t signal a new frame. I fixed it by adding a generic damage request for now. After that the picture was depicted and moving nicely.
This is definitively the first big milestone with this project. Until now all I achieved was increasing my own knowledge by reading documentation and poking into the code with debug lines. Ok, I also added some code I hoped would make sense, but besides the compilation there was no feedback through a working prototype to see if my code was going in the right direction or if it was utter bollocks. But after today I can say that my buffer flipping and committing code at least produces a picture. And when looking at the FPS counter in Neverball I would even say, that the buffer flipping replacing all the buffer copies already improved the frame rate.
But to test this I first had to solve another problem: The frame rate was always limited to the 60 Hz of my display. The reason was simple: I called present_event_notify only on the frame callback, but in the Xwayland case we can call it directly after the buffer has been sent to the compositor. The only problem I see with this is that the Present extension assumes, that after a new Pixmap has been flipped the old one can be instantly set ready to be used again for new rendering content. But if the last Pixmap’s buffer is still used by the compositor in some way this can lead to tearing.
This hints to a fundamental issue with our approach of using the Present extension in Xwayland. The extension was written with hardware in mind. It assumes a flip happens directly on a screen. There is no intermediate link like a Wayland compositor and if a flip has happened the old buffer is not on the screen anymore. Why do we still try to leverage the Present extension support in Xwayland then? There are two important features of a Wayland compositor we want to have with Xwayland: A tear-free experience for the user and the ability to output a buffer rendered by a direct rendering client on a hardware plane without any copies in between. Every frame is perfect should also remain valid when using some legacy application and that we want no unnecessary copies is simply a question of performance improvements. This is especially important for many of the more demanding games out there, which won’t be Wayland native in the short term and some of them maybe never. Both features need the the full Present extension support in the Xwayland DDX. Without it a direct rendering application would still use the Present extension but only with its fallback code path of copying the Pixmap’s content. And for a tear-free experience we would at least need to sync these copies to the frame events sent by the Wayland compositor or better directly allow multiple buffers, otherwise we would limit our frame rate. In both cases this means again to increase the Present extension support.
I plan on writing about the Present extension in detail in the next week. So if you didn’t fully understand some of the concepts I talked about in this post it could be a good idea to check back.
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| July 13, 2017 | |
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We managed to get Fedora Workstation 26 out the door this week which I am very happy about. In some ways it was far from our most splashy release as it mostly was about us improving on already released features, like improving the Wayland support and improving the Flatpak support in GNOME Software and improving the Qt integration into GNOME through the QtGNOME platform.
One major thing that is fully functional now though and that I have been testing myself extensively is being able to easily install the NVidia binary driver. If you set up the repository from Negativo17 you should be able to go install the Nvidia driver either using dnf on the command line or by searching for NVidia in GNOME Software, and just install it without any further work thanks to all the effort we and NVidia have been putting into things like glvnd. If you have a workstation with an NVidia card I would say that you have a fully functional system at this point without any hacks or file conflicts with Mesa.
For hybrid graphics laptops this also just works, with the only caveat being that your NVidia card will be engaged at all times once you do this, which is not great for your battery life. We are working to improve this, but it will take some time as it both requires us re-architecting some older parts of the stack and get the Nvidia driver updated to support the new solution.
We do plan on listing the NVidia driver in GNOME Software soon without having to manually setup the repository, so soon we will have a very smooth experience where the Nvidia driver is just a click in the Software store away for our users.
Another item of interest here for the discerning user is that if you are on the NVidia binary driver you will be using X and not Wayland. The reason for this as I have stated in previous blog posts too is that we still have some major gaps on the Wayland side when it comes to dealing with the binary NVidia driver. The biggest one here is that XWayland OpenGL applications doesn’t work, something the team is hard at work trying to resolve. Also the general infrastructure for dealing with hybrid graphics under Wayland is not there yet, but we are working on that too. We have a top notch team looking at the issues here, including Adam Jackson, Jonas Ådahl and Olivier Fourdan, so I am sure we will close this gap as soon as techically possible.
The other big item we have for Fedora Workstation 26 is going to be the formal launch of the Fleet Commander project, with a fully functional release and proper website. We hope to get that set up for next week, so I will blog more about it then. It is a really cool piece of technology which should make deploying Fedora and RHEL in large orgainzations a lot simpler.
As a sidenote, we received our first HDR capable monitor in the office this week, a Dell Ultrasharp UP2718Q. We have another one already ordered and we should be bringing in more in the next Months. This means we can finally seriously kick off figuring out the plumbing work and update the userland stack to have full HDR support under Linux for both media creation and consumption.
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| July 10, 2017 | |
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Last week I got permission to open source my work on a Mesa-based VC5 3D driver for BCM7268. You can see the announcement here which I won’t replicate on this blog. TWIVC4 is going to be a lot of TWIVC5 from here on out!
I spent the rest of the week working on fixing performance regressions when Raspbian switches from software rendering to to using the vc4 driver without a compositor enabled. The current concern is that window dragging gets slower, and in the worst case can end up with seconds of window dragging queued up behind the motion of the mouse cursor.
Past debugging of mine into how we end up with seconds of window movement queued was fruitless. I suspect it’s “each mouse position is streamed out to the window manager, and the window manager naively queues up a window move for each position it gets, rather than reading through all the position events it gets at once and sending a single move for the last one”. Instead, I worked on just seeing if we can speed up enough that we don’t care.
X11 opaque window dragging is a tough case, because unlike compositors, the contents of the window are stored on the screen (saving gobs of memory, which is important on the Raspberry Pi). When you drag the window, the src and dst regions usually overlap, so we have to be careful to not overwrite src pixels before they’ve been copied to the dst. In software rasterization, we just arrange the memcpy to happen in the correct order. For GL, we have no such control.
What glamor does instead is make a temporary copy of the src pixels, and then copy from the temp to the dst. This creates dependencies between the screen-to-temp and temp-to-screen jobs, so we flush the rendering job at least twice per copy of the window, not counting any flushes that happen for the rendering of the exposed contents from whatever was underneath the window’s old position.
In my tracing, I found that the jobs being generated during window dragging were saying that they could modify any tile on the screen, not just the tiles being affected by the copy (so we read and write each tile on the screen for those jobs). In many paths in glamor we use glScissor() to limit our rendering to some subset of the screen, and this lets the GL keep our jobs trimmed to the appropriate size. However, copies and rectangle fills were scissoring only to the destination drawable’s area, which for LXDE was everything but the global menu bar.
I made a small series that looks at small drawing operations and uses glScissor() to clip to their bounds to help tiled renderers like vc4. I was careful to try to limit the impact of these changes on non-vc4 – fast desktop renderers don’t want to spend the CPU to compute the bounds of the operations when they don’t use the bounds.
It hasn’t completely fixed RPi window dragging, but things are a lot smoother. We may find more paths that need this treatment as more people switch to using vc4 for X11 drawing.
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| July 07, 2017 | |
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After the two-part series on the fundamentals of Xwayland, I want to briefly introduce the basic idea for my Google Summer of Code (GSoC) project for X.Org. This means I’ll talk about how Xwayland currently handles the graphic buffers of its applications, why this leads to tearing and how we plan to change that.
The project has its origin in my work on KWin. In fact there is some connection to my unsuccessful GSoC application from last year on atomic mode setting and layered compositing in KWin. You can read up on these notions and the previous application in some of my older posts, but the relevant part of it to this year’s project is in short the transfer of application graphic buffers directly onto the screen without the Wayland server compositing them into a global scene before that. This can be done by putting the buffers on some overlay planes and let the hardware do the compositing of these planes into a background provided by the compositor or in the simpler case by putting a single buffer of a full screen application directly onto the primary plane.
At the beginning of the year I was working on enabling this simpler case in KWin. In a first working prototype I was pretty sure I got the basic implementation right, but my test, a full screen video in VLC, showed massive tearing. Of course I suspected at first my own code to be the problem, but in this case it wasn’t. Only after I wrote a second test application, which was a simple QML application playing the same video in full screen and showing no tearing, I had the suspicion that the problem wasn’t my code but Xwayland, since VLC was running on Xwayland while my test application was Wayland native.
Indeed the Wayland protocol should prevent tearing overall, as long as the client respects the compositor’s messages. It works like this: After committing a newly drawn buffer to the server, the client is not allowed to touch it anymore and only after the compositor has sent the release event, the client is again allowed to repaint or delete it. If the client needs to repaint in the meantime it is supposed to allocate a different buffer object. But this is exactly, what Xwayland based applications are not doing, as Daniel Stone was quick to tell me after I asked for help from him for the tearing issues I experienced.
Under Xwayland an app only ever uses one buffer at all and repaints are always done into this one buffer. This means that the buffer is given to the compositor at some point but the application doesn’t stop repainting into it. So in my case the buffer content changed, although at the same time it was presented to the user on the primary plane. The consequence is tearing. Other developers noticed that as well the same time around as documented in this bug report.
The proposed solution is to bolster the Present extension support in Xwayland. In theory with that extension an X based application should be able to paint into more than one Pixmap, which then translate to different Wayland buffers. On the other side Xwayland notifies the app through the Present extension when it can reuse one of its Pixmaps based on the associated Wayland buffer event. The Present extension is a relatively new extension to the Xserver, but is already supported by most of the more interesting applications. It was written by Keith Packard, and you can read more about it on his blog. In theory it should only be necessary to add support for the extension to the Xwayland DDX. But there are some issues in the DIX side of the extension code, which first need to be ironed out. I plan on writing more about the Present extension in general and the limitations we encounter in our Xwayland use case in the next articles.
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| July 06, 2017 | |
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Some time ago I promised to write a bit more about how shadow mapping works. It has taken me a while to bring myself to actually deliver on that front, but I have finally decided to put together some posts on this topic, this being the first one. However, before we cover shadow mapping itself we need to cover some lighting basics first. After all, without light there can’t be shadows, right?
This post will introdcuce the popular Phong reflection model as the basis for our lighting model. A lighting model provides a simplified representation of how light works in the natural world that allows us to simulate light in virtual scenes at reasonable computing costs. So let’s dive into it:
In the real world, the light that reaches an object is a combination of both direct and indirect light. Direct light is that which comes straight from a light source, while indirect light is the result of light rays hitting other surfaces in the scene, bouncing off of them and eventually reaching the object as a result, maybe after multiple reflections from other objects. Because each time a ray of light hits a surface it loses part of its energy, indirect light reflection is less bright than direct light reflection and its color might have been altered. The contrast between surfaces that are directly hit by the light source and surfaces that only receive indirect light is what creates shadows. A shadow isn’t but the part of a scene that doesn’t receive direct light but might still receive some amount of (less intense) indirect light.
Direct vs Indirect lightUnfortunately, implementing realistic light behavior like that is too expensive, specially for real-time applications, so instead we use simplifications that can produce similar results with much lower computing requirements. The Phong reflection model in particular describes the light reflected from surfaces or emitted by light sources as the combination of 3 components: diffuse, ambient and specular. The model also requires information about the direction in which a particular surface is facing, provided via vectors called surface normals. Let’s introduce each of these concepts:
When we study the behavior of light, we notice that the direction in which surfaces reflect incoming light affects our perception of the surface. For example, if we lit a shiny surface (such as a piece of metal) using a strong light shource so that incoming light is reflected off the surface in the exact opposite direction in which we are looking at it, we will see a strong reflection in the form of highlights. If we move around so that we look at the same surface from a different angle, then we will see the reflection get dimmer and the highlights will eventually disappear. In order to model this behavior we need to know the direction in which the surfaces we render reflect incoming light. The way to do this is by associating vectors called normals with the surfaces we render so that shaders can use that information to produce lighting calculations akin to what we see in the natural world.
Usually, modeling programs can compute normal vectors for us, even model loading libraries can do this work automatically, but some times, for example when we define vertex meshes programatically, we need to define them manually. I won’t covere here how to do this in the general, you can see this article from Khronos if you’re interested in specific algorithms, but I’ll point out something relevant: given a plane, we can compute normal vectors in two opposite directions, one is correct for the front face of the plane/polygon and the other one is correct for the back face, so make sure that if you compute normals manually, you use the correct direction for each face, otherwise you won’t be reflecting light in the correct direction and results won’t be as you expect.
Light reflected using correct normal vector for the front face of the triangleIn most scenarios, we only render the front faces of the polygons (by enabling back face culling) and thus, we only care about one of the normal vectors (the one for the front face).
Another thing to notice about normal vectors is that they need to be transformed with the model to be correct for transformed models: if we rotate a model we need to rotate the normals too, since the faces they represent are now rotated and thus, their normal directions have rotated too. Scaling also affects normals, specifically if we don’t use regular scaling, since in that case the orientation of the surfaces may change and affect the direction of the normal vector. Because normal vectors represent directions, their position in world space is irrelevant, so for the purpose of lighting calculations, a normal vector such as (1, 0, 0) defined for a surface placed at (0, 0, 0) is still valid to represent the same surface at any other position in the world; in other words, we do not need to apply translation transforms to our normal vectors.
In practice, the above means that we want to apply the rotation and scale transforms from our models to their normal vectors, but we can skip the translation transform. The matrix representing these transforms is usually called the normal matrix. We can compute the normal matrix from our model matrix by computing the transpose of the inverse of the 3×3 submatrix of the model matrix. Usually, we’d want to compute this matrix in the application and feed it to our vertex shader like we do with our model matrix, but for reference, here is how this can be achieved in the shader code itself, plus how to use this matrix to transform the original normal vectors:
mat3 NormalMatrix = transpose(inverse(mat3(ModelMatrix))); vec3 out_normal = normalize(NormalMatrix * in_normal);
Notice that the code above normalizes the resulting normal before it is fed to the fragment shader. This is important because the rasterizer will compute normals for all fragments in the surface automatically, and for that it will interpolate between the normals for each vertex we emit. For the interpolated normals to be correct, all vertex normals we output in the vertex shader must have the same length, otherwise the larger normals will deviate the direction of the interpolated vectors towards them because their larger size will increase their weight in the interpolation computations.
Finally, even if we emit normalized vectors in the vertex shader stage, we should note that the interpolated vectors that arrive to the fragment shader are not guaranteed to be normalized. Think for example of the normal vectors (1, 0, 0) and (0, 1, 0) being assigned to the two vertices in a line primitive. At the half-way point in between these two vertices, the interpolator will compute a normal vector of (0.5, 0.5, 0), which is not unit-sized. This means that in the general case, input normals in the fragment shader will need to be normalized again even if have normalized vertex normals at the vertex shader stage.
The diffuse component represents the reflection produced from direct light. It is important to notice that the intensity of the diffuse reflection is affected by the angle between the light coming from the source and the normal of the surface that receives the light. This makes a surface looking straight at the light source be the brightest, with reflection intensity dropping as the angle increases:
Diffuse light (spotlight source) In order to compute the diffuse component for a fragment we need its normal vector (the direction in which the surface is facing), the vector from the fragment’s position to the light source, the diffuse component of the light and the diffuse reflection of the fragment’s material:
vec3 normal = normalize(surface_normal); vec3 pos_to_light_norm = normalize(pos_to_light); float dp_reflection = max(0.0, dot(normal, pos_to_light_norm)); vec3 diffuse = material.diffuse * light.diffuse * dp_reflection;
Basically, we multiply the diffuse component of the incoming light with the diffuse reflection of the fragment’s material to produce the diffuse component of the light reflected by the fragment. The diffuse component of the surface tells how the object absorbs and reflects incoming light. For example, a pure yellow object (diffuse material vec3(1,1,0)) would absorb the blue component and reflect 100% of the red and green components of the incoming light. If the light is a pure white light (diffuse vec3(1,1,1)), then the observer would see a yellow object. However, if we are using a red light instead (diffuse vec3(1,0,0)), then the light reflected from the surface of the object would only contain the red component (since the light isn’t emitting a green component at all) and we would see it red.
As we said before though, the intensity of the reflection depends on the angle between the incoming light and the direction of the reflection. We account for this with the dot product between the normal at the fragment (surface_normal) and the direction of the light (or rather, the vector pointing from the fragment to the light source). Notice that because the vectors that we use to compute the dot product are normalized, dp_reflection is exactly the cosine of the angle between these two vectors. At an angle of 0º the surface is facing straight at the light source, and the intensity of the diffuse reflection is at its peak, since cosine(0º)=1. At an angle of 90º (or larger) the cosine will be 0 or smaller and will be clamped to 0, meaning that no light is effectively being reflected by the surface (the computed diffuse component will be 0).
Computing all possible reflections and bounces of all rays of light from each light source in a scene is way too expensive. Instead, the Phong model approximates this by making indirect reflection from a light source constant across the scene. In other words: it assumes that the amount of indirect light received by any surface in the scene is the same. This eliminates all the complexity while still producing reasonable results in most scenarios. We call this constant factor ambient light.
Ambient light Adding ambient light to the fragment is then as simple as multiplying the light source’s ambient light by the material’s ambient reflection. The meaning of this product is exactly the same as in the case of the diffuse light, only that it affects the indirect light received by the fragment:
vec3 ambient = material.ambient * light.ambient;
Very sharp, smooth surfaces such as metal are known to produce specular highlights, which are those bright spots that we can see on shiny objects. Specular reflection depends on the angle between the observer’s view direction and the direction in which the light is reflected off the surface. Specifically, the specular reflection is strongest when the observer is facing exactly in the opposite direction in which the light is reflected. Depending on the properties of the surface, the specular reflection can be more or less focused, affecting how the specular component scatters after being reflected. This property of the material is usually referred to as its shininess.
Specular light Implementing specular reflection requires a bit more of work:
vec3 specular = vec3(0);
vec3 light_dir_norm = normalize(vec3(light.direction));
if (dot(normal, -light_dir_norm) >= 0.0) {
vec3 reflection_dir = reflect(light_dir_norm, normal);
float shine_factor = dot(reflection_dir, normalize(in_view_dir));
specular = light.specular.xyz * material.specular.xyz *
pow(max(0.0, shine_factor), material.shininess.x);
}
Basically, the code above checks if there is any specular reflection at all by computing the cosine of the angle between the fragment’s normal and the direction of the light (notice that, once again, both vectors are normalized prio to using them in the call to dot()). If there is specular reflection, then we compute how shiny the reflection is perceived by the viewer based on the angle between the vector from this fragment to the observer (in_view_dir) and the direction of the light reflected off the fragment’s surface (reflection_dir). The smaller the angle, the more parallel the directions are, meaning that the camera is receiving more reflection and the specular component received is stronger. Finally, we modulate the result based on the shininess of the fragment. We can compute in_view_dir in the vertex shader using the inverse of the View matrix like this:
mat4 ViewInv = inverse(View); out_view_dir = normalize(vec3(ViewInv * vec4(0.0, 0.0, 0.0, 1.0) - world_pos));
The code above takes advantage of the fact that camera transformations are an illusion created by applying the transforms to everything else we render. For example, if we want to create the illusion that the camera is moving to the right, we just apply a translation to everything we render so they show up a bit to the left. This is what our View matrix achieves. From the point of view of GL or Vulkan, the camera is always fixed at (0,0,0). Taking advantage of this, we can compute the position of the virtual observer (the camera) in world space coordinates by applying the inverse of our camera transform to its fixed location (0,0,0). This is what the code above does, where world_pos is the position of this vertex in world space and View is the camera’s view matrix.
In order to produce the final look of the scene according to the Phong reflection model, we need to compute these 3 components for each fragment and add them together:
out_color = vec4(diffuse + ambient + specular, 1.0)
Diffuse + Ambient + Specular (spotlight source)In most scenarios, light intensity isn’t constant across the scene. Instead, it is brightest at its source and gets dimmer with distance. We can easily model this by adding an attenuation factor that is multiplied by the distance from the fragment to the light source. Typically, the intensity of the light decreases quite fast with distance, so a linear attenuation factor alone may not produce the best results and a quadratic function is preferred:
float attenuation = 1.0 /
(light.attenuation.constant +
light.attenuation.linear * dist +
light.attenuation.quadratic * dist * dist);
diffuse = diffuse * attenuation;
ambient = ambient * attenuation;
specular = specular * attenuation;
Of course, we may decide not to apply attenuation to the ambient component at all if we really want to make it look like it is constant across the scene, however, do notice that when multiple light sources are present, the ambient factors from each source will accumulate and may produce too much ambient light unless they are attenuated.
When we model a light source we also need to consider the kind of light we are manipulating:
Directional lights
These are light sources that emit rays that travel along a specific direction so that all are parallel to each other. We typically use this model to represent bright, distant light sources that produce constant light across the scene. An example would be the sun light. Because the distance to the light source is so large compared to distances in the scene, the attenuation factor is irrelevant and can be discarded. Another particularity of directional light sources is that because the light rays are parallel, shadows casted from them are regular (we will talk more about this once we cover shadow mapping in future posts).
Directional light
If we had used a directional light in the scene, it would look like this:
Scene with a directional light
Notice how the brightness of the scene doesn’t lower with the distance to the light source.
Point lights
These are light sources for which light originates at a specific position and spreads outwards in all directions. Shadows casted by point lights are not regular, instead they are projected. An example would be the light produced by a light bulb. The attenuation code I showed above would be appropriate to represent point lights.
Point light
Here is how the scene would look like with a point light:
Scene with a point lightIn this case, we can see how attenuation plays a factor and brightness lowers as we walk away from the light source (which is close to the blue cuboid).
Spotlights
This is the light source I used to illustrate the diffuse, ambient and specular components. They are similar to point lights, is the sense that light originates from a specific point in space and spreads outwards, however, instead of scattering in all directions, rays scatter forming a cone with the tip at the origin of the light. The angle formed by the lights’s direction and the sides of the cone is usually called the cutoff angle, because not light is casted outside its limits. Flashlights are a good example of this type of light.
Spotlight
In order to create spotlights we need to consider the cutoff angle of the light and make sure that no diffuse or specular component is reflected by a fragment which is beyond the cutoff threshold:
vec3 light_to_pos_norm = -pos_to_light_norm;
float dp = dot(light_to_pos_norm, light_dir_norm);
if (dp <= light.cutoff) {
diffuse = vec3(0);
specular = vec3(0);
}
In the code above we compute the cosine of the angle between the light’s direction and the vector from the light to the fragment (dp). Here, light.cutoff represents the cosine of the spotlight’s cutoff angle too, so when dp is smaller it means that the fragment is outside the light cone emitted by the spotlight and we remove its diffuse and specular reflections completely.
Handling multiple lights is easy enough: we only need to compute the color contribution for each light separately and then add all of them together for each fragment (pseudocode):
vec3 fragColor = vec3(0);
foreach light in lights
fragColor += compute_color_for_light(light, ...);
...
Of course, light attenuation plays a vital role here to limit the area of influence of each light so that scenes where we have multiple lights don’t get too bright.
An important thing to notice above the pseudocode above is that this process involves looping through costy per-fragment light computations for each light source, which can lead to important performance hits as the number of lights in the scene increases. This shading model, as described here, is called forward rendering and it has the benefit that it is very simple to implement but its downside is that we may incur in many costy lighting computations for fragments that, eventually, won’t be visible in the screen (due to them being occluded by other fragments). This is particularly important when the number of lights in the scene is quite large and its complexity makes it so that there are many occluded fragments. Another technique that may be more suitable for these situations is called deferred rendering, which postpones costy shader computations to a later stage (hence the word deferred) in which we only evaluate them for fragments that are known to be visible, but that is a topic for another day, in this series we will focus on forward rendering only.
For the purpose of shadow mapping in particular we should note that objects that are directly lit by the light source reflect all 3 of the light components, while objects in the shadow only reflect the ambient component. Because objects that only reflect ambient light are less bright, they appear shadowed, in similar fashion as they would in the real world. We will see the details how this is done in the next post, but for the time being, keep this in mind.
The scene images in this post were obtained from a simple shadow mapping demo I wrote in Vulkan. The source code for that is available here, and it includes also the shadow mapping implementation that I’ll cover in the next post. Specifically relevant to this post are the scene vertex and fragment shaders where lighting calculations take place.
In order to represent shadows we first need a means to represent light. In this post we discussed the Phong reflection model as a simple, yet effective way to model light reflection in a scene as the addition of three separate components: diffuse, ambient and specular. Once we have a representation of light we can start discussing shadows, which are parts of the scene that only receive ambient light because other objects occlude the diffuse and specular components of the light source.
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| July 04, 2017 | |
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I (finally!) merged a patchset to detect palms based on pressure into libinput. This should remove a lot of issues that our users have seen with accidental pointer movement. Palm detection in libinput previously used two approaches: disable-while-typing and an edge-based approach. The former simply ignores touchpad events while keyboard events are detected, the latter ignores touches that happen in the edge zones of the touchpad where real interaction is unlikely. Both approaches have the obvious disadvantages: they're timeout- and location-dependent, causing erroneous pointer movements. But their big advantage is that they work even on old touchpads where a lot of other information is unreliable. Touchpads are getting better, so it's time to make use of that.
The new feature is relatively simple: libinput looks at per-touch pressure and if that pressure hits a given threshold, the touch is regarded as palm. Once a palm, that touch will be ignored until touch up. The threshold is intended to be high enough that it cannot easily be hit. At least on the touchpads I have available for testing, I have to go through quite some effort to trigger palm detection with my finger.
Pressure on touchpads is unfortunately hardware-dependent and we can expect most laptops to have different pressure thresholds. For our users this means that the feature won't immediately work perfectly, it will require a lot of hwdb entries. libinput now ships a libinput measure touchpad-pressure tool to experiment with the various pressure thresholds. This makes it easy to figure out the right pressure threshold and submit a bug report (or patch) for libinput to get the pressure threshold updated. The documentation for this tool is available as part of libinput's online documentation.
TLDR: if libinput seems to misdetect touches as palms, figure out the right threshold with libinput measure touchpad-pressure and file a bug report so we can merge this into our hwdb.
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| July 01, 2017 | |
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The last couple of weeks have been consumed by getting frame sequence numbers and events handled within the leasing environment (and Vulkan) correctly.
This little extension provides the bits necessary for applications to track the display of frames to the user.
VkResult
vkGetSwapchainCounterEXT(VkDevice device,
VkSwapchainKHR swapchain,
VkSurfaceCounterFlagBitsEXT counter,
uint64_t *pCounterValue);
This function just retrieves the current frame count from the display associated with swapchain.
VkResult
vkRegisterDisplayEventEXT(VkDevice device,
VkDisplayKHR display,
const VkDisplayEventInfoEXT *pDisplayEventInfo,
const VkAllocationCallbacks *pAllocator,
VkFence *pFence);
This function creates a fence that will be signaled when the specified event happens. Right now, the only event supported is when the first pixel of the next display refresh cycle leaves the display engine for the display. If you want something fancier (like two frames from now), you get to do that on your own using this basic function.
drmWaitVBlank is the existing interface for all things sequence related and has three modes (always nice to have one function do three things, I think). It can:
This interface has a few issues:
It has been kludged into supporting multiple CRTCs by taking bits from the 'type' parameter to hold a 'pipe' number, which is the index in the kernel into the array of CRTCs.
It has a random selection of 'int' and 'long' datatypes in the interface, making it need special helpers for 32-bit apps running on a 64-bit kernel.
Times are in microseconds, frame counts are 32 bits. Vulkan does everything in nanoseconds and wants 64-bits of frame counts.
For leases, figuring out the index into the kernel list of crtcs is pretty tricky -- our lease has a subset of those crtcs, so we can't actually compute the global crtc index.
int drmCrtcGetSequence(int fd, uint32_t crtcId,
uint64_t *sequence, uint64_t *ns);
Here's a simple new function — hand it a crtc ID and it provides the current frame sequence number and the time when that frame started (in nanoseconds).
int drmCrtcQueueSequence(int fd, uint32_t crtcId,
uint32_t flags, uint64_t sequence,
uint64_t user_data);
struct drm_event_crtc_sequence {
struct drm_event base;
__u64 user_data;
__u64 time_ns;
__u64 sequence;
};
This will cause a CRTC_SEQUENCE event to be delivered at the start of the specified frame sequence. That event will include the frame when the event was actually generated (in case it's late), along with the time (in nanoseconds) when that frame was started. The event also includes a 64-bit user_data value, which can be used to hold a pointer to whatever data the application wants to see in the event handler.
The 'flags' argument contains a combination of:
#define DRM_CRTC_SEQUENCE_RELATIVE 0x00000001 /* sequence is relative to current */
#define DRM_CRTC_SEQUENCE_NEXT_ON_MISS 0x00000002 /* Use next sequence if we've missed */
#define DRM_CRTC_SEQUENCE_FIRST_PIXEL_OUT 0x00000004 /* Signal when first pixel is displayed */
These are similar to the values provided for the drmWaitVBlank function, except I've added a selector for when the event should be delivered to align with potential future additions to Vulkan. Right now, the only time you can ask for is first-pixel-out, which says that the event should correspond to the display of the first pixel on the screen.
With the kernel able to deliver a suitable event at the next frame, all the Vulkan code needed was a to create a fence and hook it up to such an event. The existing fence code only deals with rendering fences, so I added window system interface (WSI) fencing infrastructure and extended the radv driver to be able to handle both kinds of fences within that code.
I've now got three places which can be waiting for a DRM event to appear:
Frame sequence fences.
Wait for an idle image. Necessary when you want an image to draw the next frame to.
Wait for the previous flip to complete. The kernel can only queue one flip at a time, so we have to make sure the previous flip is complete before queuing another one.
Vulkan allows these to be run from separate threads, so I needed to deal with multiple threads waiting for a specific DRM event at the same time.
XCB has the same problem and goes to great lengths to manage this with a set of locking and signaling primitives so that only one thread is ever doing poll or read from the socket at time. If another thread wants to read at the same time, it will block on a condition variable which is then signaled by the original reader thread at the appropriate time. It's all very complicated, and it didn't work reliably for a number of years.
I decided to punt and just create a separate thread for processing all DRM events. It blocks using poll(2) until some events are readable, processes those and then broadcasts to a condition variable to notify any waiting threads that 'something' has happened. Each waiting thread simply checks for the desired condition and if not satisfied, blocks on that condition variable. It's all very simple looking, and seems to work just fine.
At this point, all of the necessary pieces are in place for the VR application to take advantage of an HMD using only existing Vulkan extensions. Those will be automatically mapped into DRM leases and DRM events as appropriate.
The VR compositor application is working pretty well; tests with Dota 2 show occasional jerky behavior in complex scenes, so there's clearly more work to be done somewhere. I need to go write a pile of tests to independently verify that my code is working. I wonder if I'll need to wire up some kind of light sensor so I can actually tell when frames get displayed as it's pretty easy to get consistent-but-wrong answers in this environment.
Linux. This is based off of a reasonably current drm-next branch from Dave Airlie. 965 commits past 4.12 RC3.
git://people.freedesktop.org/~keithp/linux drm-lease-v3
X server (which includes xf86-video-modesetting). This is pretty close to master.
git://people.freedesktop.org/~keithp/xserver drm-lease
RandR protocol changes
git://people.freedesktop.org/~keithp/randrproto drm-lease
xcb proto (no changes to libxcb sources, but it will need to be rebuilt)
git://people.freedesktop.org/~keithp/xcb/proto drm-lease
DRM library. About a dozen patches behind master.
git://people.freedesktop.org/~keithp/drm drm-lease
Mesa. Branched early this month (4 June), this is pretty far from master.
git://people.freedesktop.org/~keithp/mesa drm-lease
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| June 30, 2017 | |
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Last week in part one of this two part series about the fundamentals of Xwayland, we treated Xwayland like a black box. We stated what its purpose is and gave a rough overview on how it connects to its environment, notably its clients and the Wayland compositor. In a sense this was only a teaser, since we didn’t yet look at Xwayland’s inner workings. So welcome to part two, where we do a deep dive into its code base!
You can find the Xwayland code base here. Maybe to your surprise this is just the code of X.org’s Xserver, which we will just refer to as the Xserver in the rest of this text. But as a reminder from part one: Xwayland is only a normal Xserver “with a special backend written to communicate with the Wayland compositor active on your system.” This backend is located in /hw/xwayland. To understand why we find this special backend here and what I mean with an Xserver backend at all, we have to first learn some Xserver fundamentals.
The hw subdirectory is the Device Dependent X (DDX) part of the Xserver. All other directories in the source tree form the Device Independent X (DIX) part. This structuring is an important abstraction in the Xserver. Like the names suggest the DIX part is supposed to be generic enough to be the same on every imaginable hardware platform. The word hardware hereby should be understood in an abstract way as being some sort of environment the Xserver works in and has to talk to, which could be the kernel with its DRM subsystem and hardware drivers or as we already know a Wayland compositor. On the other side all code, that is potentially different with respect to the environment the Xserver is compiled for is bundled into the DDX part. Since this code is by its very definition mostly responsible for establishing and maintaining the required communication channels with the environment, we can indeed call the platform specific code paths in DDX the Xserver’s backends.
I want to emphasize that the Xserver is compiled for different environments, because we are now able to understand how the Xorg and Xwayland binaries we talked about in part one and that both implement a full Xserver come into existence: Autotools, the build system of the Xserver, is told by configuration parameters before compilation what the intended target platforms are. It then will use for each enabled target platform the respective subdirectory in hw to compile a binary with this platform’s appropriate DDX plus the generic DIX from the other top level directories. For example to compile only the Xwayland binary, you can use this command from the root of the source tree:
./autogen.sh --prefix=/usr --disable-docs --disable-devel-docs \
--enable-xwayland --disable-xorg --disable-xvfb --disable-xnest \
--disable-xquartz --disable-xwin
Coming back to the functionality let’s look at two examples in order to better understand the DIX and DDX divide and how the two parts interact with each other. Take first the concept of regions: A region specifies a certain portion of the view displayed to the user. It is defined by values for its width, height and position in some coordinate system. How regions work is therefore completely independent on the choice of hardware the Xserver runs on. That allowed the Xserver creators to put all the region code in the DIX part of the server.
Talking about regions in a view we think directly of the screen this view is displayed on. That’s the second example. We can always assume that there is some sort of real or emulated screen or even multiple of them to display our view. But how these screens and their properties are retrieved is dependent on the environment. So there needs to be some “screen code” in DDX, but on the other hand we want to move as much logic as possible in the DIX to avoid rewriting shared functionality for different platforms.
The Xserver is equipped with tools to facilitate this dichotomy. In our example about screens DIX represents the generic part of such a screen in its _Screen struct. But the struct features also the void pointer field devPrivate, which can be set by the DDX part to some struct, that then provides the device dependent information for the screen. When DIX then calls DDX to do something concerning the screen, DIX also hands over a _Screen pointer and DDX can retrieve these information through the devPrivate pointer. The private resource pointer is a tool featured in several core objects of the Xserver. For example we can also find it in the _Window struct for windows.
Besides this information sharing between DIX and DDX there are of course also procedures triggered in one part and reaching into the other one. And these procedures run according to the main event loop. We will learn more about them when we now finally analyze the Xwayland DDX code itself.
The names of the source files in the /hw/xwayland directory already indicate what they are supposed to do. Luckily there are not many of them and most of the files are rather compact. It’s quite a feat that the creators of Xwayland were able to provide X backward compatibility in a Wayland session with only that few lines of code added to the generic part of a normal Xserver. This is of course only possible thanks to the abstractions described above.
But coming back to the files here’s a table of all the files with short descriptions:
| Files | Description |
|---|---|
| xwayland.h xwayland.c |
Basically the entry point to everything else, define and implement the most central structs and functions of the Xwayland DDX. |
| xwayland-output.c | Provides a representation of a display/output. All its data is of course received from the Wayland server. |
| xwayland-cvt.c | Supports the output creation by generating a display mode calculated from available information. |
| xwayland-input.c | Deals with inputs provided by mice and other input devices. As you can see by its size, it’s not the most straight forward area to work on. |
| xwayland-cursor.c | Makes a cursor appear. That is in a graphic pipeline often treated as a special case to reduce repaints. |
| xwayland-glamor.c xwayland-shm.c |
Provide two different ways for allocating graphic buffers. |
| xwayland-glamor-xv.c xwayland-vidmode.c |
Support for hardware accelerated video playback and older games, what is in parts not yet fully functional. |
In the following we will restrict our analysis to the xwayland.* files, in order to keep the growing length of this article in check.
Some basic structs and functions also shared with the other source files are defined in the header file xwayland.h. A good first point to remember is, that all structs and functions with names starting on xwl_ are only known to the Xwayland DDX and won’t be called from anywhere else. But at the beginning of the xwayland.c file we find some methods without the prefix. They are only defined in the DIX and their implementation is required to make Xwayland a fully functional DDX.
Scrolling down to the end of the file we see the main entry point to the DDX on server startup, the InitOutput method. If you look closely you will notice a call to AddScreen, where we also hook up an Xwayland internal screen init function as one of its arguments. But it’s only called once! So what about multiple screens? The explanation is, that Xwayland uses the RandR extension for its screen management and here only asks for the creation of one screen struct as a dummy, which holds on runtime some global information about the Wayland environment. We looked at this particular screen struct in the previous chapter as an example for information sharing between DIX and DDX through void pointers and that these pointers are set by the DDX.
Although it’s only a dummy, we can still follow this now live in action in the hooked up init function xwl_screen_init. Here we set with the help of some DIX methods a hash key to later identify the data field again and then set the data, which is an xwl_screen struct with static information about the Wayland environment the Xwayland server is deployed in.
In the hooked up init function the later manipulation of the function pointers RealizeWindow, UnrealizeWindow and so on is also quite interesting. I asked Daniel about it, because I didn’t understand at all the steps done here as well as similar ones later in the involved functions xwl_realize_window, xwl_unrealize_window and so on. Daniel explained the mechanism well to me and it is quite nifty indeed. Basically thanks to this trick, called wrapping, Xwayland and other DDX can intercept DIX calls to a procedure like RealizeWindow, execute their own code, and then go on with the procedure looking to the DIX like it never happened.
In the case of RealizeWindow, which is called when a window was created and is now ready to be displayed, we intercept it with xwl_realize_window, where an Xwayland internal representation of type struct xwl_window is allocated with all the Xwayland specific additional information, in particular a Wayland surface. At the end the request to create the surface is sent to the Wayland server via the Wayland protocol. You can probably imagine what UnrealizeWindow and the wrapped xwl_unrealize_window is supposed to do and that it does this in a very similar way.
As a last point let’s look at the event loop and the buffer dispatch of possibly new or changed graphical content. We have block_handler, which was registered in xwl_screen_init to the DIX, and gets called continuously throughout the event loop. From here we call into a global damage posting function and from there for each window into xwl_window_post_damage. If we’re lucky we get a buffer with hardware acceleration from the implementation in xwayland-glamor.c or otherwise without acceleration from the one in xwayland-shm.c, attach it to the surface and fire it away. In the next event loop we play the same game.
Forcing an end to this article, what we ignored in total is input handling in Xwayland and we also only touched the graphics buffer in the end. But at least the graphic buffers we’ll discuss in the coming weeks exhaustively, since my Google Summer of Code project is all about these little guys.
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| June 27, 2017 | |
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GALLIUM_HUD is a feature that adds performance graphs to applications that describe various aspects like FPS, CPU usage, etc in realtime.
It is enabled using an environment variable, GALLIUM_HUD, that can be set for GL/EGL/etc applications. It only works for Mesa drivers that are Gallium based, which means that the most drivers (with the notable exception of some Intel drivers) support GALLIUM_HUD.
See GALLIUM_HUD options:
export GALLIUM_HUD=help
glxgears
If you're building Android, you can supply system-wide environment values by doing an export in the init.rc file of the device you are using, like this.
# Go to android source code checkout
cd android
# Add export to init.rc (linaro/generic is the device I use)
nano device/linaro/generic/init …GALLIUM_HUD is a feature that adds performance graphs to applications that describe various aspects like FPS, CPU usage, etc in realtime.
It is enabled using an environment variable, GALLIUM_HUD, that can be set for GL/EGL/etc applications. It only works for Mesa drivers that are Gallium based, which means that the most drivers (with the notable exception of some Intel drivers) support GALLIUM_HUD.
See GALLIUM_HUD options:
export GALLIUM_HUD=help
glxgears
If you're building Android, you can supply system-wide environment values by doing an export in the init.rc file of the device you are using, like this.
# Go to android source code checkout
cd android
# Add export to init.rc (linaro/generic is the device I use)
nano device/linaro/generic/init …After blogging about
casync
I realized I never blogged about the
mkosi tool that combines nicely
with it. mkosi has been around for a while already, and its time to
make it a bit better known. mkosi stands for Make Operating System
Image, and is a tool for precisely that: generating an OS tree or
image that can be booted.
Yes, there are many tools like mkosi, and a number of them are quite
well known and popular. But mkosi has a number of features that I
think make it interesting for a variety of use-cases that other tools
don't cover that well.
What are those use-cases, and what does mkosi precisely set apart?
mkosi is definitely a tool with a focus on developer's needs for
building OS images, for testing and debugging, but also for generating
production images with cryptographic protection. A typical use-case
would be to add a mkosi.default file to an existing project (for
example, one written in C or Python), and thus making it easy to
generate an OS image for it. mkosi will put together the image with
development headers and tools, compile your code in it, run your test
suite, then throw away the image again, and build a new one, this time
without development headers and tools, and install your build
artifacts in it. This final image is then "production-ready", and only
contains your built program and the minimal set of packages you
configured otherwise. Such an image could then be deployed with
casync (or any other tool of course) to be delivered to your set of
servers, or IoT devices or whatever you are building.
mkosi is supposed to be legacy-free: the focus is clearly on
today's technology, not yesteryear's. Specifically this means that
we'll generate GPT partition tables, not MBR/DOS ones. When you tell
mkosi to generate a bootable image for you, it will make it bootable
on EFI, not on legacy BIOS. The GPT images generated follow
specifications such as the Discoverable Partitions
Specification,
so that /etc/fstab can remain unpopulated and tools such as
systemd-nspawn can automatically dissect the image and boot from
them.
So, let's have a look on the specific images it can generate:
When any of the GPT choices above are selected, a couple of additional options are available:
/home and /srv may be added in/home and /srv partitions may be optionally encrypted with LUKSdm-verity, thus making offline attacks on the generated system harddm-verity root hash is automatically added to the kernel command line, and the kernel together with its initial RAM disk and the kernel command line is optionally cryptographically signed for UEFI SecureBootNote that mkosi is distribution-agnostic. It currently can build
images based on the following Linux distributions:
Note though that not all distributions are supported at the same
feature level currently. Also, as mkosi is based on dnf
--installroot, debootstrap, pacstrap and zypper, and those
packages are not packaged universally on all distributions, you might
not be able to build images for all those distributions on arbitrary
host distributions.
The GPT images are put together in a way that they aren't just
compatible with UEFI systems, but also with VM and container managers
(that is, at least the smart ones, i.e. VM managers that know UEFI,
and container managers that grok GPT disk images) to a large
degree. In fact, the idea is that you can use mkosi to build a
single GPT image that may be used to:
systemd-nspawn containerRootImage= unit file settingNote that in all four cases the dm-verity data is automatically used
if available to ensure the image is not tampered with (yes, you read
that right, systemd-nspawn and systemd's RootImage= setting
automatically do dm-verity these days if the image has it.)
The simplest usage of mkosi is by simply invoking it without
parameters (as root):
# mkosi
Without any configuration this will create a GPT disk image for you,
will call it image.raw and drop it in the current directory. The
distribution used will be the same one as your host runs.
Of course in most cases you want more control about how the image is
put together, i.e. select package sets, select the distribution, size
partitions and so on. Most of that you can actually specify on the
command line, but it is recommended to instead create a couple of
mkosi.$SOMETHING files and directories in some directory. Then,
simply change to that directory and run mkosi without any further
arguments. The tool will then look in the current working directory
for these files and directories and make use of them (similar to how
make looks for a Makefile…). Every single file/directory is
optional, but if they exist they are honored. Here's a list of the
files/directories mkosi currently looks for:
mkosi.default — This is the main configuration file, here you
can configure what kind of image you want, which distribution, which
packages and so on.
mkosi.extra/ — If this directory exists, then mkosi will copy
everything inside it into the images built. You can place arbitrary
directory hierarchies in here, and they'll be copied over whatever is
already in the image, after it was put together by the distribution's
package manager. This is the best way to drop additional static files
into the image, or override distribution-supplied ones.
mkosi.build — This executable file is supposed to be a build
script. When it exists, mkosi will build two images, one after the
other in the mode already mentioned above: the first version is the
build image, and may include various build-time dependencies such as
a compiler or development headers. The build script is also copied
into it, and then run inside it. The script should then build
whatever shall be built and place the result in $DESTDIR (don't
worry, popular build tools such as Automake or Meson all honor
$DESTDIR anyway, so there's not much to do here explicitly). It may
also run a test suite, or anything else you like. After the script
finished, the build image is removed again, and a second image (the
final image) is built. This time, no development packages are
included, and the build script is not copied into the image again —
however, the build artifacts from the first run (i.e. those placed in
$DESTDIR) are copied into the image.
mkosi.postinst — If this executable script exists, it is invoked
inside the image (inside a systemd-nspawn invocation) and can
adjust the image as it likes at a very late point in the image
preparation. If mkosi.build exists, i.e. the dual-phased
development build process used, then this script will be invoked
twice: once inside the build image and once inside the final
image. The first parameter passed to the script clarifies which phase
it is run in.
mkosi.nspawn — If this file exists, it should contain a
container configuration file for systemd-nspawn (see
systemd.nspawn(5)
for details), which shall be shipped along with the final image and
shall be included in the check-sum calculations (see below).
mkosi.cache/ — If this directory exists, it is used as package
cache directory for the builds. This directory is effectively bind
mounted into the image at build time, in order to speed up building
images. The package installers of the various distributions will
place their package files here, so that subsequent runs can reuse
them.
mkosi.passphrase — If this file exists, it should contain a
pass-phrase to use for the LUKS encryption (if that's enabled for the
image built). This file should not be readable to other users.
mkosi.secure-boot.crt and mkosi.secure-boot.key should be an
X.509 key pair to use for signing the kernel and initrd for UEFI
SecureBoot, if that's enabled.
So, let's come back to our most trivial example, without any of the
mkosi.$SOMETHING files around:
# mkosi
As mentioned, this will create a build file image.raw in the current
directory. How do we use it? Of course, we could dd it onto some USB
stick and boot it on a bare-metal device. However, it's much simpler
to first run it in a container for testing:
# systemd-nspawn -bi image.raw
And there you go: the image should boot up, and just work for you.
Now, let's make things more interesting. Let's still not use any of
the mkosi.$SOMETHING files around:
# mkosi -t raw_btrfs --bootable -o foobar.raw
# systemd-nspawn -bi foobar.raw
This is similar as the above, but we made three changes: it's no
longer GPT + ext4, but GPT + btrfs. Moreover, the system is made
bootable on UEFI systems, and finally, the output is now called
foobar.raw.
Because this system is bootable on UEFI systems, we can run it in KVM:
qemu-kvm -m 512 -smp 2 -bios /usr/share/edk2/ovmf/OVMF_CODE.fd -drive format=raw,file=foobar.raw
This will look very similar to the systemd-nspawn invocation, except
that this uses full VM virtualization rather than container
virtualization. (Note that the way to run a UEFI qemu/kvm instance
appears to change all the time and is different on the various
distributions. It's quite annoying, and I can't really tell you what
the right qemu command line is to make this work on your system.)
Of course, it's not all raw GPT disk images with mkosi. Let's try
a plain directory image:
# mkosi -d fedora -t directory -o quux
# systemd-nspawn -bD quux
Of course, if you generate the image as plain directory you can't boot it on bare-metal just like that, nor run it in a VM.
A more complex command line is the following:
# mkosi -d fedora -t raw_squashfs --checksum --xz --package=openssh-clients --package=emacs
In this mode we explicitly pick Fedora as the distribution to use, ask
mkosi to generate a compressed GPT image with a root squashfs,
compress the result with xz, and generate a SHA256SUMS file with
the hashes of the generated artifacts. The package will contain the
SSH client as well as everybody's favorite editor.
Now, let's make use of the various mkosi.$SOMETHING files. Let's
say we are working on some Automake-based project and want to make it
easy to generate a disk image off the development tree with the
version you are hacking on. Create a configuration file:
# cat > mkosi.default <<EOF
[Distribution]
Distribution=fedora
Release=24
[Output]
Format=raw_btrfs
Bootable=yes
[Packages]
# The packages to appear in both the build and the final image
Packages=openssh-clients httpd
# The packages to appear in the build image, but absent from the final image
BuildPackages=make gcc libcurl-devel
EOF
And let's add a build script:
# cat > mkosi.build <<EOF
#!/bin/sh
./autogen.sh
./configure --prefix=/usr
make -j `nproc`
make install
EOF
# chmod +x mkosi.build
And with all that in place we can now build our project into a disk image, simply by typing:
# mkosi
Let's try it out:
# systemd-nspawn -bi image.raw
Of course, if you do this you'll notice that building an image like this can be quite slow. And slow build times are actively hurtful to your productivity as a developer. Hence let's make things a bit faster. First, let's make use of a package cache shared between runs:
# mkdir mkosi.cache
Building images now should already be substantially faster (and
generate less network traffic) as the packages will now be downloaded
only once and reused. However, you'll notice that unpacking all those
packages and the rest of the work is still quite slow. But mkosi can
help you with that. Simply use mkosi's incremental build feature. In
this mode mkosi will make a copy of the build and final images
immediately before dropping in your build sources or artifacts, so
that building an image becomes a lot quicker: instead of always
starting totally from scratch a build will now reuse everything it can
reuse from a previous run, and immediately begin with building your
sources rather than the build image to build your sources in. To
enable the incremental build feature use -i:
# mkosi -i
Note that if you use this option, the package list is not updated anymore from your distribution's servers, as the cached copy is made after all packages are installed, and hence until you actually delete the cached copy the distribution's network servers aren't contacted again and no RPMs or DEBs are downloaded. This means the distribution you use becomes "frozen in time" this way. (Which might be a bad thing, but also a good thing, as it makes things kinda reproducible.)
Of course, if you run mkosi a couple of times you'll notice that it
won't overwrite the generated image when it already exists. You can
either delete the file yourself first (rm image.raw) or let mkosi
do it for you right before building a new image, with mkosi -f. You
can also tell mkosi to not only remove any such pre-existing images,
but also remove any cached copies of the incremental feature, by using
-f twice.
I wrote mkosi originally in order to test systemd, and quickly
generate a disk image of various distributions with the most current
systemd version from git, without all that affecting my host system. I
regularly use mkosi for that today, in incremental mode. The two
commands I use most in that context are:
# mkosi -if && systemd-nspawn -bi image.raw
And sometimes:
# mkosi -iff && systemd-nspawn -bi image.raw
The latter I use only if I want to regenerate everything based on the very newest set of RPMs provided by Fedora, instead of a cached snapshot of it.
BTW, the mkosi files for systemd are included in the systemd git
tree:
mkosi.default
and
mkosi.build. This
way, any developer who wants to quickly test something with current
systemd git, or wants to prepare a patch based on it and test it can
check out the systemd repository and simply run mkosi in it and a
few minutes later he has a bootable image he can test in
systemd-nspawn or KVM. casync has similar files:
mkosi.default,
mkosi.build.
As mentioned already, mkosi will generate dm-verity enabled
disk images if you ask for it. For that use the --verity switch on
the command line or Verity= setting in mkosi.default. Of course,
dm-verity implies that the root volume is read-only. In this mode
the top-level dm-verity hash will be placed along-side the output
disk image in a file named the same way, but with the .roothash
suffix. If the image is to be created bootable, the root hash is also
included on the kernel command line in the roothash= parameter,
which current systemd versions can use to both find and activate the
root partition in a dm-verity protected way. BTW: it's a good idea
to combine this dm-verity mode with the raw_squashfs image mode,
to generate a genuinely protected, compressed image suitable for
running in your IoT device.
As indicated above, mkosi can automatically create a check-sum
file SHA256SUMS for you (--checksum) covering all the files it
outputs (which could be the image file itself, a matching .nspawn
file using the mkosi.nspawn file mentioned above, as well as the
.roothash file for the dm-verity root hash.) It can then
optionally sign this with gpg (--sign). Note that systemd's
machinectl pull-tar and machinectl pull-raw command can download
these files and the SHA256SUMS file automatically and verify things
on download. With other words: what mkosi outputs is perfectly
ready for downloads using these two systemd commands.
As mentioned, mkosi is big on supporting UEFI SecureBoot. To
make use of that, place your X.509 key pair in two files
mkosi.secureboot.crt and mkosi.secureboot.key, and set
SecureBoot= or --secure-boot. If so, mkosi will sign the
kernel/initrd/kernel command line combination during the build. Of
course, if you use this mode, you should also use
Verity=/--verity=, otherwise the setup makes only partial
sense. Note that mkosi will not help you with actually enrolling
the keys you use in your UEFI BIOS.
mkosi has minimal support for GIT checkouts: when it recognizes
it is run in a git checkout and you use the mkosi.build script
stuff, the source tree will be copied into the build image, but will
all files excluded by .gitignore removed.
There's support for encryption in place. Use --encrypt= or
Encrypt=. Note that the UEFI ESP is never encrypted though, and the
root partition only if explicitly requested. The /home and /srv
partitions are unconditionally encrypted if that's enabled.
Images may be built with all documentation removed.
The password for the root user and additional kernel command line arguments may be configured for the image to generate.
Current mkosi requires Python 3.5, and has a number of dependencies,
listed in the
README. Most
notably you need a somewhat recent systemd version to make use of its
full feature set: systemd 233. Older versions are already packaged for
various distributions, but much of what I describe above is only
available in the most recent release mkosi 3.
The UEFI SecureBoot support requires sbsign which currently isn't
available in Fedora, but there's a
COPR.
It is my intention to continue turning mkosi into a tool suitable
for:
One of the biggest goals I have for the future is to teach mkosi and
systemd/sd-boot native support for A/B IoT style partition
setups. The idea is that the combination of systemd, casync and
mkosi provides generic building blocks for building secure,
auto-updating devices in a generic way from, even though all pieces
may be used individually, too.
Why are you reinventing the wheel again? This is exactly like
$SOMEOTHERPROJECT! — Well, to my knowledge there's no tool that
integrates this nicely with your project's development tree, and can
do dm-verity and UEFI SecureBoot and all that stuff for you. So
nope, I don't think this exactly like $SOMEOTHERPROJECT, thank you
very much.
What about creating MBR/DOS partition images? — That's really out of focus to me. This is an exercise in figuring out how generic OSes and devices in the future should be built and an attempt to commoditize OS image building. And no, the future doesn't speak MBR, sorry. That said, I'd be quite interested in adding support for booting on Raspberry Pi, possibly using a hybrid approach, i.e. using a GPT disk label, but arranging things in a way that the Raspberry Pi boot protocol (which is built around DOS partition tables), can still work.
Is this portable? — Well, depends what you mean by
portable. No, this tool runs on Linux only, and as it uses
systemd-nspawn during the build process it doesn't run on
non-systemd systems either. But then again, you should be able to
create images for any architecture you like with it, but of course if
you want the image bootable on bare-metal systems only systems doing
UEFI are supported (but systemd-nspawn should still work fine on
them).
Where can I get this stuff? — Try GitHub. And some distributions carry packaged versions, but I think none of them the current v3 yet.
Is this a systemd project? — Yes, it's hosted under the
systemd GitHub umbrella. And yes,
during run-time systemd-nspawn in a current version is required. But
no, the code-bases are separate otherwise, already because systemd
is a C project, and mkosi Python.
Requiring systemd 233 is a pretty steep requirement, no? —
Yes, but the feature we need kind of matters (systemd-nspawn's
--overlay= switch), and again, this isn't supposed to be a tool for
legacy systems.
Can I run the resulting images in LXC or Docker? — Humm, I am
not an LXC nor Docker guy. If you select directory or subvolume
as image type, LXC should be able to boot the generated images just
fine, but I didn't try. Last time I looked, Docker doesn't permit
running proper init systems as PID 1 inside the container, as they
define their own run-time without intention to emulate a proper
system. Hence, no I don't think it will work, at least not with an
unpatched Docker version. That said, again, don't ask me questions
about Docker, it's not precisely my area of expertise, and quite
frankly I am not a fan. To my knowledge neither LXC nor Docker are
able to run containers directly off GPT disk images, hence the
various raw_xyz image types are definitely not compatible with
either. That means if you want to generate a single raw disk image
that can be booted unmodified both in a container and on bare-metal,
then systemd-nspawn is the container manager to go for
(specifically, its -i/--image= switch).
Well, that's up to you really.
If you hack on some complex project and need a quick way to compile
and run your project on a specific current Linux distribution, then
mkosi is an excellent way to do that. Simply drop the mkosi.default
and mkosi.build files in your git tree and everything will be
easy. (And of course, as indicated above: if the project you are
hacking on happens to be called systemd or casync be aware that
those files are already part of the git tree — you can just use them.)
If you hack on some embedded or IoT device, then mkosi is a great
choice too, as it will make it reasonably easy to generate secure
images that are protected against offline modification, by using
dm-verity and UEFI SecureBoot.
If you are an administrator and need a nice way to build images for a
VM or systemd-nspawn container, or a portable service then mkosi
is an excellent choice too.
If you care about legacy computers, old distributions, non-systemd
init systems, old VM managers, Docker, … then no, mkosi is not for
you, but there are plenty of well-established alternatives around that
cover that nicely.
And never forget: mkosi is an Open Source project. We are happy to
accept your patches and other contributions.
Oh, and one unrelated last thing: don't forget to submit your talk
proposal
and/or buy a ticket for
All Systems Go! 2017 in Berlin — the
conference where things like systemd, casync and mkosi are
discussed, along with a variety of other Linux userspace projects used
for building systems.
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| June 26, 2017 | |
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This week I picked up my old vc4-xml branch. This rework was inspired by the Intel driver, where they wrote an XML description of the hardware packets and use that to code-generate the packet packing and debug dumping code. Given that vc4’s debug dumping has always been somewhat of a mess (and its code is duplicated between mesa and vc4-gpu-tools), it would be great to do the same thing to vc4. More importantly, the XML-generated pack code easily lets you do things like precompute part of your packed state packet at gallium CSO generation time, and then just memcpy (or OR together two copies) at draw time.
My problem with the branch had been that it bloated the size of the vc4_emit.c code (the draw-time path), which probably meant that it reduced performance compared to my old hand-written packing. I had spent a couple of weeks writing fast paths for things like moving a float into the unaligned CL, or packing a couple of flag bits into the bottom of a 32-bit address, but that only took the bloat from like 20% to 10%. Last week, I decided to stop using the size as a proxy for performance and just test performance, and it turns out that the difference was negligible or slightly positive! Now I need to get an Android build done, and merge.
In the process of doing this draw overhead testing, I turned on a new gallium flag that cut the CPU overhead of draw calls by 5%, which was more than any of my vc4-xml overhead ever was!
I also spent more time on the 7” panel again, trying a rework of the load order in response to review feedback. It turns out that the DSI portion of DRM isn’t built to support drivers the way that previous feedback requested, and nobody has a concrete plan for how it would work. I’ve tried one avenue of fixing it, but that ran into another mess in the DSI subsystem.
Switching Raspbian over to vc4 fkms is currently stalled on Simon rebuilding the packages with the current Mesa patchset. I’ve fixed a minor issue in the fkms overlay that requested aligned CMA areas despite my having removed that requirement a while back, so hopefully they’ll finally enable vc4 on Pi0/1 as well once they get around to updating.
I did another round of review on the piglit series for ANDROID_native_fence and they’re ready to land now.
I sent out a rework to make some VC4 NIR lowering code shareable with other drivers. Freedreno and Intel have both wanted it at some point, so hopefully I can get some review on it.
In the kernel, I polished up my BO-labeling code that gives you detailed graphics memory usage information in /debug/dri/0/bo_stats. The cleanup was to effectively eliminate the CPU overhead, unless you choose do labeling from userspace. Adding this userspace interface required adding intel-gpu-tools testcases, so I wrote those. The Mesa side isn’t merged yet since we need kernel review first, and will probably only be enabled in debug driver builds. To make it really fancy, I should also hook up glObjectLabel() all the way to the kernel, so that /debug/dri/0/bo_stats can have things like “X11 ARGB glyph cache” instead of “resource 1024x1024@4” for that mystery 4MB buffer you’ve got.
Finally, I did some cleanup of the VC4 modesetting code, prompted by Boris’s recent cleanups. We’re much closer to matching the common DRM helpers now, with just our async pageflip code still being special. Once Gustavo’s async cursor bits land, we may be able to remove our async pageflip special case as well!
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| June 25, 2017 | |
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| June 23, 2017 | |
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In this week’s article for my ongoing Google Summer of Code (GSoC) project I planned on writing about the basic idea behind the project, but I reconsidered and decided to first give an overview on how Xwayland functions on a high-level and in the next week take a look at its inner workings in detail. The reason for that is, that there is not much Xwayland documentation available right now. So these two articles are meant to fill this void in order to give interested beginners a helping hand. And in two weeks I’ll catch up on explaining the project’s idea.
As we go high level this week the first question is, what is Xwayland supposed to achieve at all? You may know this. It’s something in a Wayland session ensuring that applications, which don’t support Wayland but only the old Xserver still function normally, i.e. it ensures backwards compatibility. But how does it do this? Before we go into this, there is one more thing to talk about, since I called Xwayland only something before. What is Xwayland exactly? How does it look to you on your Linux system? We’ll see in the next week that it’s not as easy to answer as the following simple explanation makes it appear, but for now this is enough: It’s a single binary containing an Xserver with a special backend written to communicate with the Wayland compositor active on your system - for example with KWin in a Plasma Wayland session.
To make it more tangible let’s take a look at Debian: There is a package called Xwayland and it consists of basically only the aforementioned binary file. This binary gets copied to /usr/bin/Xwayland. Compare this to the normal Xserver provided by X.org, which in Debian you can find in the package xserver-xorg-core. The respective binary gets put into /usr/bin/Xorg together with a symlink /usr/bin/X pointing to it.
While the latter is the central building block in an X session and therefore gets launched before anything else with graphical output, the Xserver in the Xwayland binary works differently: It is embedded in a Wayland session. And in a Wayland session the Wayland compositor is the central building block. This means in particular that the Wayland compositor also takes up the role of being the server, who talks to Wayland native applications with graphical output as its clients. They send request to it in order to present their painted stuff on the screen. The Xserver in the Xwayland binary is only a necessary link between applications, which are only able to speak to an Xserver, and the Wayland compositor/server. Therefore the Xwayland binary gets launched later on by the compositor or some other process in the workspace. In Plasma it’s launched by KWin after the compositor has initialized the rendering pipeline. You find the relevant code here.
Although in this case KWin also establishes some communication channels with the newly created Xwayland process, in general the communication between Xwayland and a Wayland server is done by the normal Wayland protocoll in the same way other native Wayland applications talk to the compositor/server. This means the windows requested by possibly several X based applications and provided by Xwayland acting as an Xserver are translated at the same time by Xwayland to Wayland compatible objects and, acting as a native Wayland client, send to the Wayland compositor via the Wayland protocol. These windows look to the Wayland compositor just like the windows - in Wayland terminology surfaces - of every other Wayland native application. When reading this keep in mind, that an application in Wayland is not limited to using only one window/surface but can create multiple at the same time, so Xwayland as a native Wayland client can do the same for all the windows created for all of its X clients.
In the second part next week we’ll have a close look at the Xwayland code to see how Xwayland fills its role as an Xserver in regards to its X based clients and at the same time acts as a Wayland client when facing the Wayland compositor.
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| June 20, 2017 | |
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Felt it been to long since I did another Fedora Workstation update. We spend a lot of time trying to figure out how we can best spend our resources to produce the best desktop possible for our users, because even though Red Hat invests more into the Linux desktop than any other company by quite a margin, our resources are still far from limitless. So we have a continuous effort of asking ourselves if each of the areas we are investing in are the right ones that give our users the things they need the most, so below is a sampling of the things we are working on.
Improving integration of the NVidia binary driver
This has been ongoing for quite a while, but things have started to land now. Hans de Goede and Simone Caronni has been collaboring, building on the work by NVidia and Adam Jackson around glvnd. So if you set up Simones NVidia repository hosted on negativo17 you will be able to install the Nvidia driver without any conflicts with the Mesa stack and due to Hans work you should be fairly sure that even if the NVidia driver stops working with a given kernel update you will smoothly transition back to the open source Nouveau driver. I been testing it on my own Lenovo P70 system for the last week and it seems to work well under X. That said once you install the binary NVidia driver that is what your running on, which is of course not the behaviour you want from a hybrid graphics system. Fixing that last issue requires further collaboration between us and NVidia.
Related to this Adam Jackson is currently working on a project he calls glxmux. glxmux will allow you to have more than one GLX implementation on the system, so that you can switch between Mesa GLX for the Intel integrated graphics card and NVidia GLX for the binary driver. While we can make no promises we hope to have the framework in place for Fedora Workstation 27. Having that in place should allow us to create a solution where you only use the NVidia driver when you want the extra graphics power which will of course require significant work from Nvidia to enable it on their side so I can’t give a definite timeline for when all the puzzle pieces are in place. Just be assured we are working on it and talking regularly to NVidia about it. I will let you know here as soon as things come together.
On the Wayland side the Jonas Ådahl is working on putting the final touches on Hybrid Graphics support
Fleet Commander ready for take-off
Another major project we been working on for a long time in Fleet Commander. Fleet Commander is a tool to allow you to manage Fedora and RHEL desktops centrally. This is a tool targeted at for instance Universities or companies with tens, hundreds or thousands of workstation installation. It gives you a graphical browser based UI (accessible through Cockpit) to create configuration profiles and deploy across your organization. Currently it allows you to control anything that has a gsetting associated with it like enabling/disabling extensions and setting configuration settings in GTK+ and GNOME applications. It allows you to configure Network Manager settings so if your updating the company VPN or proxy settings you can easily push those changes out to all user in the organization. Or quickly migrate Evolution email settings to a new email server. The tool also allows you to control recommended applications in the Software Center and set bookmarks in Firefox. There is also support for controlling settings inside LibreOffice.
All this features can be set and controlled on either a user level or a group level or organization wide due to the close integration we have with FreeIPA suite of tools. The data is stored inside your organizations LDAP server alongside other user information so you don’t need to have the clients connect to a new service for this, and while it is not there in this initial release we will in the future also support Active Directory.
The initial release and Fleet Commander website will be out alongside Fedora Workstation 26.
PipeWire
I talked about PipeWire before, when it was still called Pinos, but the scope and ambition for the project has significantly changed since then. Last time when I spoke about it the goal was just to create something that could be considered a video equivalent of pulseaudio. Wim Taymans, who you might know co-created GStreamer and who has been a major PulseAudio contributor, has since expanded the scope and PipeWire now aims at unifying linux Audio and Video. The long term the goal is for PipeWire to not only provide handling of video streams, but also handle all kinds of audio. Due to this Wim has been spending a lot of time making sure PipeWire can handle audio in a way that not only address the PulseAudio usecases, but also the ones handled by Jack today. A big part of the motivation for this is that we want to make Fedora Workstation the best place to create content and we want the pro-audio crowd to be first class citizens of our desktop.
At the same time we don’t want to make this another painful subsystem transition so PipeWire so we will need to ensure that PulseAudio applications can still be run without modification.
We expect to start shipping PipeWire with Fedora Workstation 27, but at that point only have it handle video as we need this to both enable good video handling for Flatpak applications through a video portal, but also to provide an API for applications that want to do screen capture under Wayland, like web browser applications offering screen sharing. We will the bring the audio features onboard in subsequent releases as we also try to work with the Jack and PulseAudio communities to make this a joint effort. We are also working now on a proper website for PipeWire.
Red Hat developer integration
A feature we are quite excited about is the integration of support for the Red Hat developer account system into Fedora. This means that you should be able to create a Red Hat developer account through GNOME Online accounts and once you have that account set up you should be able to easily create Red Hat Enterprise Linux virtual machines or containers on your Fedora system. This is a crucial piece for the developer focus that we want the workstation to have and one that we think will make a lot of developers life easier. We where originally hoping to have this ready for Fedora Workstaton 26, but atm it looks more likely to hit Fedora Workstation 27, but we will keep you up to date as this progresses.
Fractional scaling for HiDPI systems
Fedora Workstation has been leading the charge in supporting HiDPI on Linux and we hope to build on that with the current work to enable fractional scaling support. Since we introduced HiDPI support we have been improving it step by step, for instance last year we introduced support for dealing with different DPI levels per monitor for Wayland applications. The fractional scaling work will take this a step further. The biggest problem it will resolve is that for certain monitor sizes the current scaling options either left things to small or to big. With the fractional scaling support we will introduce intermediate steps, so that you can scale your interface 1.5x times instead of having to go all the way to 2. The set of technologies we are developing for handling fractional scaling should also allow us to provide better scaling for XWayland applications as it provides us with methods for scaling that doesn’t need direct support from the windowing system or toolkit.
GNOME Shell performance
Carlos Garnacho has been doing some great work recently improving the general performance of GNOME Shell. This comes on top of his earlier performance work that was very well received. How fast/slow GNOME shell is often a subjective thing, but reducing overhead where we can is never a bad thing.
Flatpak building
Owen Taylor has been working hard on putting the pieces in place for start large scale Flatpak building in Fedora. You might see a couple of test flatpaks appear in a Fedora Workstation 26 timeframe, but the goal is to have a huge Flatpak catalog ready in time for Fedora Workstation 27. Essentially what we are doing is making it very simple for a Fedora maintainer to build a Flatpak of the application they maintain through the Fedora package building infrastructure and push that Flatpak into a central Flatpak registry. And while of course this is mainly meant to be to the benefit of Fedora users there is of course nothing stopping other distributions from offering these Flatpak packaged applications to their users also.
Atomic Workstation
Another effort that is marching forward is what we call Atomic Workstation. The idea here is to have an immutable OS image kinda like what you see on for instance Android devices. The advantage to this is that the core of the operating system gets tested and deployed as a unit and the chance of users ending with broken systems decrease significantly as we don’t need to rely on packages getting applied in the correct order or scripts executing as expected on each individual workstation out there. This effort is largely based on the Project Atomic effort, and the end goal here is to have a image based OS install and Flatpak based applications on top of it. If you are very adventerous and/or want to help out with this effort you can get the ISO image installer for Atomic Workstation here.
Firmware handling
Our Linux Firmware project is still going strong with new features being added and new vendors signing on. As Richard Hughes recently blogged about the latest vendor joining the effort is Logitech who now will upload their firmware into the service so that you can keep your Logitech peripherals updated through it. It is worthwhile pointing out here how we worked with Logitech to make this happen, with Richard working on the special tooling needed and thus reducing the threshold for Logitech to start offering their firmware through the service. We have other vendors we are having similar discussions and collaborations with so expect to see more. At this point I tend to recommend people get a Dell to run Linux, due to their strong support for efforts such as the Linux Firmware Service, but other major vendors are in the final stages of testing so expect more major vendors starting to push firmware updates soon.
High Dynamic Range
The next big thing in the display technology field is HDR (High Dynamic Range). HDR allows for deeper more vibrant colours and is a feature seen on a lot of new TVs these days and game consoles like the Playstation 4 support it. Computer monitors are appearing on the market too now with this feature, for instance the Dell UP2718Q. We want to ensure Fedora and Linux is a leader here, for the benefit of video and graphics artists using Fedora and Red Hat Enterprise Linux. We are thus kicking of an effort to make sure this technology mature as quickly as possible and be fully supported. We are not the only ones interested in this so we will hopefully be collaborating with our friends at Intel, AMD and NVidia on this. We hope to have the first monitors delivered to our office within a few weeks.
Codecs
While playback these days have moved to streaming where locally installed codecs are of less importance for the consumption usecase, having a wide selection of codecs available is still important for media editing and creation usecases, so we want you to be able to load a varity of old media files into you video editor for instance. Luckily we are at a crossroads now where a lot of widely used codecs have their essential patents expire (mp3, ac3 and more) while at the same time the industry focus seems to have moved to royalty free codec development moving forward (Opus, VP9, Alliance for Open Media). We have been spending a lot of time with the Red Hat legal team trying to clear these codecs, which resulted in mp3 and AC3 now shipping in Fedora Workstation. We have more codecs on the way though, so this effort is in no way over. My goal is that over the course of this year the situation of software patents being a huge issue when dealing with audio and video codecs on Linux will be considered a thing of the past. I would like to thank the Red Hat legal team for their support on this issue as they have had to spend significant time on it as a big company like Red Hat do need to do our own due diligence when it comes to these things, we can’t just trust statements from random people on the internet that these codecs are now free to ship.
Battery life
We been looking at this for a while now and hope to be able to start sharing information with users on which laptops they should get that will have good battery life under Fedora. Christian Kellner is now our point man on battery life and he has taken up improving the Battery Bench tool that Owen Taylor wrote some time ago.
QtGNOME platform
We will have a new version of the QtGNOME platform in Fedora 26. For those of you who have not yet heard of this effort it is a set of themes and tools to ensure that Qt applications runs without any major issues under GNOME 3. With the new version the theming expands to include the accessibility and dark themes in Adwaita, meaning that if you switch to one of these themes under GNOME shell it will also switch your Qt applications over. We are also making sure things like cut’n paste and drag and drop works well. The version in Fedora Workstation 26 is a big step forward for this effort and should hopefully make Qt applications be first class citizens under your Fedora Workstation desktop.
Wayland polish
Ever since we switched the default to Wayland we have kept the pressure up and kept fixing bugs and finding solutions for corner cases. The result should be an improved Wayland experience in Fedora Workstation 26. A big thanks for Olivier Fourdan, Jonas Ådahl and the whole Wayland community for their continued efforts here. Two major items Jonas is working on for instance is improving fractional scaling, to ensure that your desktop scales to an optimal size on HiDPI displays of various sizes. What we currently have is limited to 1x or 2x, which is either to small or to big for some screens, but with this work you can also do 1.5x scaling. He is also working on preparing an API that will allow screen sharing under Wayland, so that for instance sharing your slides over video conferencing can work under Wayland.
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| June 19, 2017 | |
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In the past months I have been working on a new project:
casync. casync takes
inspiration from the popular rsync file
synchronization tool as well as the probably even more popular
git revision control system. It combines the
idea of the rsync algorithm with the idea of git-style
content-addressable file systems, and creates a new system for
efficiently storing and delivering file system images, optimized for
high-frequency update cycles over the Internet. Its current focus is
on delivering IoT, container, VM, application, portable service or OS
images, but I hope to extend it later in a generic fashion to become
useful for backups and home directory synchronization as well (but
more about that later).
The basic technological building blocks casync is built from are
neither new nor particularly innovative (at least not anymore),
however the way casync combines them is different from existing tools,
and that's what makes it useful for a variety of use-cases that other
tools can't cover that well.
I created casync after studying how today's popular tools store and
deliver file system images. To briefly name a few: Docker has a
layered tarball approach,
OSTree serves the
individual files directly via HTTP and maintains packed deltas to
speed up updates, while other systems operate on the block layer and
place raw squashfs images (or other archival file systems, such as
IS09660) for download on HTTP shares (in the better cases combined
with zsync data).
Neither of these approaches appeared fully convincing to me when used in high-frequency update cycle systems. In such systems, it is important to optimize towards a couple of goals:
I don't think any of the tools mentioned above are really good on more than a small subset of these points.
Specifically: Docker's layered tarball approach dumps the "delta" question onto the feet of the image creators: the best way to make your image downloads minimal is basing your work on an existing image clients might already have, and inherit its resources, maintaining full history. Here, revision control (a tool for the developer) is intermingled with update management (a concept for optimizing production delivery). As container histories grow individual deltas are likely to stay small, but on the other hand a brand-new deployment usually requires downloading the full history onto the deployment system, even though there's no use for it there, and likely requires substantially more disk space and download sizes.
OSTree's serving of individual files is unfriendly to CDNs (as many small files in file trees cause an explosion of HTTP GET requests). To counter that OSTree supports placing pre-calculated delta images between selected revisions on the delivery servers, which means a certain amount of revision management, that leaks into the clients.
Delivering direct squashfs (or other file system) images is almost
beautifully simple, but of course means every update requires a full
download of the newest image, which is both bad for disk usage and
generated traffic. Enhancing it with zsync makes this a much better
option, as it can reduce generated traffic substantially at very
little cost of history/meta-data (no explicit deltas between a large
number of versions need to be prepared server side). On the other hand
server requirements in disk space and functionality (HTTP Range
requests) are minus points for the use-case I am interested in.
(Note: all the mentioned systems have great properties, and it's not my intention to badmouth them. They only point I am trying to make is that for the use case I care about — file system image delivery with high high frequency update-cycles — each system comes with certain drawbacks.)
Besides the issues pointed out above I wasn't happy with the security
and reproducibility properties of these systems. In today's world
where security breaches involving hacking and breaking into connected
systems happen every day, an image delivery system that cannot make
strong guarantees regarding data integrity is out of
date. Specifically, the tarball format is famously nondeterministic:
the very same file tree can result in any number of different
valid serializations depending on the tool used, its version and the
underlying OS and file system. Some tar implementations attempt to
correct that by guaranteeing that each file tree maps to exactly
one valid serialization, but such a property is always only specific
to the tool used. I strongly believe that any good update system must
guarantee on every single link of the chain that there's only one
valid representation of the data to deliver, that can easily be
verified.
So much about the background why I created casync. Now, let's have a
look what casync actually is like, and what it does. Here's the brief
technical overview:
Encoding: Let's take a large linear data stream, split it into variable-sized chunks (the size of each being a function of the chunk's contents), and store these chunks in individual, compressed files in some directory, each file named after a strong hash value of its contents, so that the hash value may be used to as key for retrieving the full chunk data. Let's call this directory a "chunk store". At the same time, generate a "chunk index" file that lists these chunk hash values plus their respective chunk sizes in a simple linear array. The chunking algorithm is supposed to create variable, but similarly sized chunks from the data stream, and do so in a way that the same data results in the same chunks even if placed at varying offsets. For more information see this blog story.
Decoding: Let's take the chunk index file, and reassemble the large linear data stream by concatenating the uncompressed chunks retrieved from the chunk store, keyed by the listed chunk hash values.
As an extra twist, we introduce a well-defined, reproducible,
random-access serialization format for file trees (think: a more
modern tar), to permit efficient, stable storage of complete file
trees in the system, simply by serializing them and then passing them
into the encoding step explained above.
Finally, let's put all this on the network: for each image you want to deliver, generate a chunk index file and place it on an HTTP server. Do the same with the chunk store, and share it between the various index files you intend to deliver.
Why bother with all of this? Streams with similar contents will result in mostly the same chunk files in the chunk store. This means it is very efficient to store many related versions of a data stream in the same chunk store, thus minimizing disk usage. Moreover, when transferring linear data streams chunks already known on the receiving side can be made use of, thus minimizing network traffic.
Why is this different from rsync or OSTree, or similar tools? Well,
one major difference between casync and those tools is that we
remove file boundaries before chunking things up. This means that
small files are lumped together with their siblings and large files
are chopped into pieces, which permits us to recognize similarities in
files and directories beyond file boundaries, and makes sure our chunk
sizes are pretty evenly distributed, without the file boundaries
affecting them.
The "chunking" algorithm is based on a the buzhash rolling hash function. SHA256 is used as strong hash function to generate digests of the chunks. xz is used to compress the individual chunks.
Here's a diagram, hopefully explaining a bit how the encoding process works, wasn't it for my crappy drawing skills:
The diagram shows the encoding process from top to bottom. It starts with a block device or a file tree, which is then serialized and chunked up into variable sized blocks. The compressed chunks are then placed in the chunk store, while a chunk index file is written listing the chunk hashes in order. (The original SVG of this graphic may be found here.)
Note that casync operates on two different layers, depending on the
use-case of the user:
You may use it on the block layer. In this case the raw block data on disk is taken as-is, read directly from the block device, split into chunks as described above, compressed, stored and delivered.
You may use it on the file system layer. In this case, the
file tree serialization format mentioned above comes into play:
the file tree is serialized depth-first (much like tar would do
it) and then split into chunks, compressed, stored and delivered.
The fact that it may be used on both the block and file system layer opens it up for a variety of different use-cases. In the VM and IoT ecosystems shipping images as block-level serializations is more common, while in the container and application world file-system-level serializations are more typically used.
Chunk index files referring to block-layer serializations carry the
.caibx suffix, while chunk index files referring to file system
serializations carry the .caidx suffix. Note that you may also use
casync as direct tar replacement, i.e. without the chunking, just
generating the plain linear file tree serialization. Such files
carry the .catar suffix. Internally .caibx are identical to
.caidx files, the only difference is semantical: .caidx files
describe a .catar file, while .caibx files may describe any other
blob. Finally, chunk stores are directories carrying the .castr
suffix.
Here are a couple of other features casync has:
When downloading a new image you may use casync's --seed=
feature: each block device, file, or directory specified is processed
using the same chunking logic described above, and is used as
preferred source when putting together the downloaded image locally,
avoiding network transfer of it. This of course is useful whenever
updating an image: simply specify one or more old versions as seed and
only download the chunks that truly changed since then. Note that
using seeds requires no history relationship between seed and the new
image to download. This has major benefits: you can even use it to
speed up downloads of relatively foreign and unrelated data. For
example, when downloading a container image built using Ubuntu you can
use your Fedora host OS tree in /usr as seed, and casync will
automatically use whatever it can from that tree, for example timezone
and locale data that tends to be identical between
distributions. Example: casync extract
http://example.com/myimage.caibx --seed=/dev/sda1 /dev/sda2. This
will place the block-layer image described by the indicated URL in the
/dev/sda2 partition, using the existing /dev/sda1 data as seeding
source. An invocation like this could be typically used by IoT systems
with an A/B partition setup. Example 2: casync extract
http://example.com/mycontainer-v3.caidx --seed=/srv/container-v1
--seed=/srv/container-v2 /src/container-v3, is very similar but
operates on the file system layer, and uses two old container versions
to seed the new version.
When operating on the file system level, the user has fine-grained
control on the meta-data included in the serialization. This is
relevant since different use-cases tend to require a different set of
saved/restored meta-data. For example, when shipping OS images, file
access bits/ACLs and ownership matter, while file modification times
hurt. When doing personal backups OTOH file ownership matters little
but file modification times are important. Moreover different backing
file systems support different feature sets, and storing more
information than necessary might make it impossible to validate a tree
against an image if the meta-data cannot be replayed in full. Due to
this, casync provides a set of --with= and --without= parameters
that allow fine-grained control of the data stored in the file tree
serialization, including the granularity of modification times and
more. The precise set of selected meta-data features is also always
part of the serialization, so that seeding can work correctly and
automatically.
casync tries to be as accurate as possible when storing file
system meta-data. This means that besides the usual baseline of file
meta-data (file ownership and access bits), and more advanced features
(extended attributes, ACLs, file capabilities) a number of more exotic
data is stored as well, including Linux
chattr(1) file attributes, as
well as FAT file
attributes
(you may wonder why the latter? — EFI is FAT, and /efi is part of
the comprehensive serialization of any host). In the future I intend
to extend this further, for example storing btrfs sub-volume
information where available. Note that as described above every single
type of meta-data may be turned off and on individually, hence if you
don't need FAT file bits (and I figure it's pretty likely you don't),
then they won't be stored.
The user creating .caidx or .caibx files may control the desired
average chunk length (before compression) freely, using the
--chunk-size= parameter. Smaller chunks increase the number of
generated files in the chunk store and increase HTTP GET load on the
server, but also ensure that sharing between similar images is
improved, as identical patterns in the images stored are more likely
to be recognized. By default casync will use a 64K average chunk
size. Tweaking this can be particularly useful when adapting the
system to specific CDNs, or when delivering compressed disk images
such as squashfs (see below).
Emphasis is placed on making all invocations reproducible,
well-defined and strictly deterministic. As mentioned above this is a
requirement to reach the intended security guarantees, but is also
useful for many other use-cases. For example, the casync digest
command may be used to calculate a hash value identifying a specific
directory in all desired detail (use --with= and --without to pick
the desired detail). Moreover the casync mtree command may be used
to generate a BSD mtree(5) compatible manifest of a directory tree,
.caidx or .catar file.
The file system serialization format is nicely composable. By this I mean that the serialization of a file tree is the concatenation of the serializations of all files and file sub-trees located at the top of the tree, with zero meta-data references from any of these serializations into the others. This property is essential to ensure maximum reuse of chunks when similar trees are serialized.
When extracting file trees or disk image files, casync
will automatically create
reflinks
from any specified seeds if the underlying file system supports it
(such as btrfs, ocfs, and future xfs). After all, instead of
copying the desired data from the seed, we can just tell the file
system to link up the relevant blocks. This works both when extracting
.caidx and .caibx files — the latter of course only when the
extracted disk image is placed in a regular raw image file on disk,
rather than directly on a plain block device, as plain block devices
do not know the concept of reflinks.
Optionally, when extracting file trees, casync can
create traditional UNIX hard-links for identical files in specified
seeds (--hardlink=yes). This works on all UNIX file systems, and can
save substantial amounts of disk space. However, this only works for
very specific use-cases where disk images are considered read-only
after extraction, as any changes made to one tree will propagate to
all other trees sharing the same hard-linked files, as that's the
nature of hard-links. In this mode, casync exposes OSTree-like
behavior, which is built heavily around read-only hard-link trees.
casync tries to be smart when choosing what to include in file
system images. Implicitly, file systems such as procfs and sysfs are
excluded from serialization, as they expose API objects, not real
files. Moreover, the "nodump" (+d)
chattr(1) flag is honored by
default, permitting users to mark files to exclude from serialization.
When creating and extracting file trees casync may apply an
automatic or explicit UID/GID shift. This is particularly useful when
transferring container image for use with Linux user name-spacing.
In addition to local operation, casync currently supports HTTP,
HTTPS, FTP and ssh natively for downloading chunk index files and
chunks (the ssh mode requires installing casync on the remote host,
though, but an sftp mode not requiring that should be easy to
add). When creating index files or chunks, only ssh is supported as
remote back-end.
When operating on block-layer images, you may expose locally or
remotely stored images as local block devices. Example: casync mkdev
http://example.com/myimage.caibx exposes the disk image described by
the indicated URL as local block device in /dev, which you then may
use the usual block device tools on, such as mount or fdisk (only
read-only though). Chunks are downloaded on access with high priority,
and at low priority when idle in the background. Note that in this
mode, casync also plays a role similar to "dm-verity", as all blocks
are validated against the strong digests in the chunk index file
before passing them on to the kernel's block layer. This feature is
implemented though Linux' NBD kernel facility.
Similar, when operating on file-system-layer images, you may mount
locally or remotely stored images as regular file systems. Example:
casync mount http://example.com/mytree.caidx /srv/mytree mounts the
file tree image described by the indicated URL as a local directory
/srv/mytree. This feature is implemented though Linux' FUSE kernel
facility. Note that special care is taken that the images exposed this
way can be packed up again with casync make and are guaranteed to
return the bit-by-bit exact same serialization again that it was
mounted from. No data is lost or changed while passing things through
FUSE (OK, strictly speaking this is a lie, we do lose ACLs, but that's
hopefully just a temporary gap to be fixed soon).
In IoT A/B fixed size partition setups the file systems placed in
the two partitions are usually much shorter than the partition size,
in order to keep some room for later, larger updates. casync is able
to analyze the super-block of a number of common file systems in order
to determine the actual size of a file system stored on a block
device, so that writing a file system to such a partition and reading
it back again will result in reproducible data. Moreover this speeds
up the seeding process, as there's little point in seeding the
white-space after the file system within the partition.
Here's how to use casync, explained with a few examples:
$ casync make foobar.caidx /some/directory
This will create a chunk index file foobar.caidx in the local
directory, and populate the chunk store directory default.castr
located next to it with the chunks of the serialization (you can
change the name for the store directory with --store= if you
like). This command operates on the file-system level. A similar
command operating on the block level:
$ casync make foobar.caibx /dev/sda1
This command creates a chunk index file foobar.caibx in the local
directory describing the current contents of the /dev/sda1 block
device, and populates default.castr in the same way as above. Note
that you may as well read a raw disk image from a file instead of a
block device:
$ casync make foobar.caibx myimage.raw
To reconstruct the original file tree from the .caidx file and
the chunk store of the first command, use:
$ casync extract foobar.caidx /some/other/directory
And similar for the block-layer version:
$ casync extract foobar.caibx /dev/sdb1
or, to extract the block-layer version into a raw disk image:
$ casync extract foobar.caibx myotherimage.raw
The above are the most basic commands, operating on local data only. Now let's make this more interesting, and reference remote resources:
$ casync extract http://example.com/images/foobar.caidx /some/other/directory
This extracts the specified .caidx onto a local directory. This of
course assumes that foobar.caidx was uploaded to the HTTP server in
the first place, along with the chunk store. You can use any command
you like to accomplish that, for example scp or
rsync. Alternatively, you can let casync do this directly when
generating the chunk index:
$ casync make ssh.example.com:images/foobar.caidx /some/directory
This will use ssh to connect to the ssh.example.com server, and then
places the .caidx file and the chunks on it. Note that this mode of
operation is "smart": this scheme will only upload chunks currently
missing on the server side, and not re-transmit what already is
available.
Note that you can always configure the precise path or URL of the
chunk store via the --store= option. If you do not do that, then the
store path is automatically derived from the path or URL: the last
component of the path or URL is replaced by default.castr.
Of course, when extracting .caidx or .caibx files from remote sources,
using a local seed is advisable:
$ casync extract http://example.com/images/foobar.caidx --seed=/some/exising/directory /some/other/directory
Or on the block layer:
$ casync extract http://example.com/images/foobar.caibx --seed=/dev/sda1 /dev/sdb2
When creating chunk indexes on the file system layer casync will by
default store meta-data as accurately as possible. Let's create a chunk
index with reduced meta-data:
$ casync make foobar.caidx --with=sec-time --with=symlinks --with=read-only /some/dir
This command will create a chunk index for a file tree serialization that has three features above the absolute baseline supported: 1s granularity time-stamps, symbolic links and a single read-only bit. In this mode, all the other meta-data bits are not stored, including nanosecond time-stamps, full UNIX permission bits, file ownership or even ACLs or extended attributes.
Now let's make a .caidx file available locally as a mounted file
system, without extracting it:
$ casync mount http://example.comf/images/foobar.caidx /mnt/foobar
And similar, let's make a .caibx file available locally as a block device:
$ casync mkdev http://example.comf/images/foobar.caibx
This will create a block device in /dev and print the used device
node path to STDOUT.
As mentioned, casync is big about reproducibility. Let's make use of
that to calculate the a digest identifying a very specific version of
a file tree:
$ casync digest .
This digest will include all meta-data bits casync and the underlying
file system know about. Usually, to make this useful you want to
configure exactly what meta-data to include:
$ casync digest --with=unix .
This makes use of the --with=unix shortcut for selecting meta-data
fields. Specifying --with-unix= selects all meta-data that
traditional UNIX file systems support. It is a shortcut for writing out:
--with=16bit-uids --with=permissions --with=sec-time --with=symlinks
--with=device-nodes --with=fifos --with=sockets.
Note that when calculating digests or creating chunk indexes you may
also use the negative --without= option to remove specific features
but start from the most precise:
$ casync digest --without=flag-immutable
This generates a digest with the most accurate meta-data, but leaves
one feature out: chattr(1)'s
immutable (+i) file flag.
To list the contents of a .caidx file use a command like the following:
$ casync list http://example.com/images/foobar.caidx
or
$ casync mtree http://example.com/images/foobar.caidx
The former command will generate a brief list of files and
directories, not too different from tar t or ls -al in its
output. The latter command will generate a BSD
mtree(5) compatible
manifest. Note that casync actually stores substantially more file
meta-data than mtree files can express, though.
casync is not an attempt to minimize serialization and downloaded
deltas to the extreme. Instead, the tool is supposed to find a good
middle ground, that is good on traffic and disk space, but not at the
price of convenience or requiring explicit revision control. If you
care about updates that are absolutely minimal, there are binary delta
systems around that might be an option for you, such as Google's
Courgette.
casync is not a replacement for rsync, or git or zsync or
anything like that. They have very different use-cases and
semantics. For example, rsync permits you to directly synchronize two
file trees remotely. casync just cannot do that, and it is unlikely
it every will.
casync is supposed to be a generic synchronization tool. Its primary
focus for now is delivery of OS images, but I'd like to make it useful
for a couple other use-cases, too. Specifically:
To make the tool useful for backups, encryption is missing. I have
pretty concrete plans how to add that. When implemented, the tool
might become an alternative to restic,
BorgBackup or
tarsnap.
Right now, if you want to deploy casync in real-life, you still
need to validate the downloaded .caidx or .caibx file yourself, for
example with some gpg signature. It is my intention to integrate with
gpg in a minimal way so that signing and verifying chunk index files
is done automatically.
In the longer run, I'd like to build an automatic synchronizer for
$HOME between systems from this. Each $HOME instance would be
stored automatically in regular intervals in the cloud using casync,
and conflicts would be resolved locally.
casync is written in a shared library style, but it is not yet
built as one. Specifically this means that almost all of casync's
functionality is supposed to be available as C API soon, and
applications can process casync files on every level. It is my
intention to make this library useful enough so that it will be easy
to write a module for GNOME's gvfs subsystem in order to make remote
or local .caidx files directly available to applications (as an
alternative to casync mount). In fact the idea is to make this all
flexible enough that even the remoting back-ends can be replaced
easily, for example to replace casync's default HTTP/HTTPS back-ends
built on CURL with GNOME's own HTTP implementation, in order to share
cookies, certificates, … There's also an alternative method to
integrate with casync in place already: simply invoke casync as a
sub-process. casync will inform you about a certain set of state
changes using a mechanism compatible with
sd_notify(3). In
future it will also propagate progress data this way and more.
I intend to a add a new seeding back-end that sources chunks from
the local network. After downloading the new .caidx file off the
Internet casync would then search for the listed chunks on the local
network first before retrieving them from the Internet. This should
speed things up on all installations that have multiple similar
systems deployed in the same network.
Further plans are listed tersely in the TODO file.
Is this a systemd project? — casync is hosted under the
github systemd umbrella, and the
projects share the same coding style. However, the code-bases are
distinct and without interdependencies, and casync works fine both
on systemd systems and systems without it.
Is casync portable? — At the moment: no. I only run Linux and
that's what I code for. That said, I am open to accepting portability
patches (unlike for systemd, which doesn't really make sense on
non-Linux systems), as long as they don't interfere too much with the
way casync works. Specifically this means that I am not too
enthusiastic about merging portability patches for OSes lacking the
openat(2) family
of APIs.
Does casync require reflink-capable file systems to work, such
as btrfs? — No it doesn't. The reflink magic in casync is
employed when the file system permits it, and it's good to have it,
but it's not a requirement, and casync will implicitly fall back to
copying when it isn't available. Note that casync supports a number
of file system features on a variety of file systems that aren't
available everywhere, for example FAT's system/hidden file flags or
xfs's projinherit file flag.
Is casync stable? — I just tagged the first, initial
release. While I have been working on it since quite some time and it
is quite featureful, this is the first time I advertise it publicly,
and it hence received very little testing outside of its own test
suite. I am also not fully ready to commit to the stability of the
current serialization or chunk index format. I don't see any breakages
coming for it though. casync is pretty light on documentation right
now, and does not even have a man page. I also intend to correct that
soon.
Are the .caidx/.caibx and .catar file formats open and
documented? — casync is Open Source, so if you want to know the
precise format, have a look at the sources for now. It's definitely my
intention to add comprehensive docs for both formats however. Don't
forget this is just the initial version right now.
casync is just like $SOMEOTHERTOOL! Why are you reinventing
the wheel (again)? — Well, because casync isn't "just like" some
other tool. I am pretty sure I did my homework, and that there is no
tool just like casync right now. The tools coming closest are probably
rsync, zsync, tarsnap, restic, but they are quite different beasts
each.
Why did you invent your own serialization format for file trees?
Why don't you just use tar? — That's a good question, and other
systems — most prominently tarsnap — do that. However, as mentioned
above tar doesn't enforce reproducibility. It also doesn't really do
random access: if you want to access some specific file you need to
read every single byte stored before it in the tar archive to find
it, which is of course very expensive. The serialization casync
implements places a focus on reproducibility, random access, and
meta-data control. Much like traditional tar it can still be
generated and extracted in a stream fashion though.
Does casync save/restore SELinux/SMACK file labels? — At the
moment not. That's not because I wouldn't want it to, but simply
because I am not a guru of either of these systems, and didn't want to
implement something I do not fully grok nor can test. If you look at
the sources you'll find that there's already some definitions in place
that keep room for them though. I'd be delighted to accept a patch
implementing this fully.
What about delivering squashfs images? How well does chunking
work on compressed serializations? – That's a very good point!
Usually, if you apply the a chunking algorithm to a compressed data
stream (let's say a tar.gz file), then changing a single bit at the
front will propagate into the entire remainder of the file, so that
minimal changes will explode into major changes. Thankfully this
doesn't apply that strictly to squashfs images, as it provides
random access to files and directories and thus breaks up the
compression streams in regular intervals to make seeking easy. This
fact is beneficial for systems employing chunking, such as casync as
this means single bit changes might affect their vicinity but will not
explode in an unbounded fashion. In order achieve best results when
delivering squashfs images through casync the block sizes of
squashfs and the chunks sizes of casync should be matched up
(using casync's --chunk-size= option). How precisely to choose
both values is left a research subject for the user, for now.
What does the name casync mean? – It's a synchronizing
tool, hence the -sync suffix, following rsync's naming. It makes
use of the content-addressable concept of git hence the ca-
prefix.
Where can I get this stuff? Is it already packaged? – Check
out the sources on GitHub. I
just tagged the first
version. Martin
Pitt has packaged casync for
Ubuntu. There
is also an ArchLinux
package. Zbigniew
Jędrzejewski-Szmek has prepared a Fedora
RPM that hopefully
will soon be included in the distribution.
Well, that's up to you really. If you are involved with projects that need to deliver IoT, VM, container, application or OS images, then maybe this is a great tool for you — but other options exist, some of which are linked above.
Note that casync is an Open Source project: if it doesn't do exactly
what you need, prepare a patch that adds what you need, and we'll
consider it.
If you are interested in the project and would like to talk about this
in person, I'll be presenting casync soon at Kinvolk's Linux
Technologies
Meetup
in Berlin, Germany. You are invited. I also intend to talk about it at
All Systems Go!, also in Berlin.
The All Systems Go! 2017 Call for Participation is Now Open!
We’d like to invite presentation proposals for All Systems Go! 2017!
All Systems Go! is an Open Source community conference focused on the projects and technologies at the foundation of modern Linux systems — specifically low-level user-space technologies. Its goal is to provide a friendly and collaborative gathering place for individuals and communities working to push these technologies forward.
All Systems Go! 2017 takes place in Berlin, Germany on October 21st+22nd.
All Systems Go! is a 2-day event with 2-3 talks happening in parallel. Full presentation slots are 30-45 minutes in length and lightning talk slots are 5-10 minutes.
We are now accepting submissions for presentation proposals. In particular, we are looking for sessions including, but not limited to, the following topics:
While our focus is definitely more on the user-space side of things, talks about kernel projects are welcome too, as long as they have a clear and direct relevance for user-space.
Please submit your proposals by September 3rd. Notification of acceptance will be sent out 1-2 weeks later.
To submit your proposal now please visit our CFP submission web site.
For further information about All Systems Go! visit our conference web site.
systemd.conf will not take place this year in lieu of All Systems Go!. All Systems Go! welcomes all projects that contribute to Linux user space, which, of course, includes systemd. Thus, anything you think was appropriate for submission to systemd.conf is also fitting for All Systems Go!
I just released the first release candidate for libinput 1.8. Aside from the build system switch to meson one of the more visible things is that the helper tools have switched from a "libinput-some-tool" to the "libinput some-tool" approach (note the space). This is similar to what git does so it won't take a lot of adjustment for most developers. The actual tools are now hiding in /usr/libexec/libinput. This gives us a lot more flexibility in writing testing and debugging tools and shipping them to the users without cluttering up the default PATH.
There are two potential breakages here, one is that the two existing tools libinput-debug-events and libinput-list-devices have been renamed too. We currently ship compatibility wrappers for those but expect those wrappers to go away with future releases. The second breakage is of lesser impact: typing "man libinput" used to bring up the man page for the xf86-input-libinput driver. Now it brings up the man page for the libinput tool which then points to the man pages of the various features. That's probably a good thing, it puts the documentation a bit closer to the user. For the driver, you now have to type "man 4 libinput" though.
Last week I got review on the new interface for tiling for vc4, and landed it in the kernel. I’ve submitted Mesa patches to the list, landed the kernel backport in Raspbian, and have sent Simon (the package maintainer at the Foundation) the Mesa patchset to backport all of my work from the last 6 months (unfortunately Raspbian generally doesn’t update Mesa past the Debian stable release, so graphics work for them has long delays). I also worked with Dom at the Foundation to get an interface for the firmwarekms mode to do tiled scanout, so it will be as fast as the open source driver.
I also reworked the official 7” touchscreen panel driver again. I had initially written it as a DSI panel driver, then got told it should be a bridge driver plus a panel driver, then the bridge maintainers told me it should be only one panel driver but attach to I2C. Maybe this version will stick, who knows.
My Mesa side for pl111 is now in master, so I’ve got the second platform for the vc4 driver basically done. I can’t wait to do another one.
I got a question about whether VC4 could do EGL_ANDROID_native_fence, to allow using Android’s hwcomposer (the display server that puts surfaces in KMS planes if it can). I spent a while looking into it, and found that while code had landed in Mesa for other drivers, the piglit tests had been left around untouched for the last half a year. I reviewed them and hopefully they can land soon. Unfortunately, they don’t cover the important functionality of the extension, so I can’t use them to actually write the driver code (which doesn’t look very hard) until I build some more tests.
On the non-vc4 kernel side, I prepared and submitted pull requests for 4.13. We’ve got USB OTG support for the Pi Zero, SDHOST enabled by default finally, thermal enabled by default finally, and the RPi3 DT being installed for 32-bit kernels. Three of these took months longer than they should have, because the Linux kernel has the worst software development process I’ve worked with since XFree86.
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| June 16, 2017 | |
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There is a saying that persistence is the key to success. Not that I’m always following this advice, but I did luckily earlier this year when I had to decide if I wanted to apply again for a Google Summer of Code (GSoC) spot after my application in the last year was rejected by my organisation of choice back then. I talked about it in one of my last posts. Anyway, thanks to being persistent this year one of my project ideas got accepted and I now have the opportunity to work on a very interesting project concerning Xwayland, this time for the X.Org Foundation.
The project is kind of difficult though. At least it feels this way to me right now, after I’ve already spent quite some time on digging into it and getting a feel for it.
The main reason for the difficulty is, that various components of the XServer are in play and documentation for them is most often missing. Would I be on my own, I could basically only work with the code and try to comprehend the steps done one after the other. I’m not on my own though! With Daniel Stone I have one of the core developers of several key parts of the Linux graphic stack as my mentor, who seems to really want to help me to understand the difficult stuff on a large scale and still gives concrete advice on what to do next. He even drew a diagram for me!
I plan on publishing in future blog posts resources like this otherwise clearly underused diagram, since such material to understand the XServer code is otherwise only sparsely to find on the web. Additionally I’ll try to explain the idea of my project and the general structure of the code I’m dealing with in my own words. Regarding these future posts a nasty surprise for me was this week, that it’s expected from me to publish one blog post per week about my project. This somewhat spoils my plans for this blog, where I wanted to publish very few but in comparison more sophisticated posts. Nevertheless you can therefore expect to have frequent weekly posts until August. Next week I want to explain the basic idea of my project.
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| June 15, 2017 | |
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| June 09, 2017 | |
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| June 03, 2017 | |
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| June 02, 2017 | |
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Back in 2003, the pressure range value for Wacom pen tablets was set to 2048. That's a #define in the driver, but it shouldn't matter because we also advertise this range as part of the device description in the X Input protocol. Clients should be using that advertised min/max range and scale appropriately, in the same way as they should be doing this for the x/y axis ranges.
Fast-forward to 2017 and we changed the pressure range. New Wacom devices now use ~8000 levels, but we opted to just #define it in the driver to 65536 and be done with it. We now scale all models into that range, with varying granularity based on the physical hardware. It shouldn't matter because it's not tied to a reliable physical property anyway and the only thing that matters is the percentage of the max value (which is why libinput just gives you a [0, 1] range. Hindsight is a bliss.).
Slow-forward to 2017-and-a-bit and we received complaints that pressure handling is now broken. Turns out that some applications hardcoded the old 2048 range and now get confused, because virtually any pressure will now hit that maximum. Since those applications are largely proprietary ones and cannot be updated easily, we needed a workaround to this. Jason Gerecke from Wacom got busy and we now have a "Pressure2K" option available in the driver. If set, this option will scale everything into the 2048 range to make sure those applications still work. To get this to work, the following xorg.conf.d snippet is recommended:
Put it in a file that sorts higher than the wacom driver itself (e.g. /etc/X11/xorg.conf.d/99-wacom-pressure2k.conf) and restart X. Check the Xorg.log/journal for a "Using 2K pressure levels" message, then verify it works by running xinput list "device name". xinput should show a range of 0 to 2048 on the third valuator.
Section "InputClass"
Identifier "Wacom pressure compatibility"
MatchDriver "wacom"
Option "Pressure2K" "true"
EndSection
$> xinput list "Wacom Intuos4 6x9 Pen stylus"
Wacom Intuos4 6x9 Pen stylus id=25 [slave pointer (2)]
Reporting 8 classes:
Class originated from: 25. Type: XIButtonClass
Buttons supported: 9
Button labels: None None None None None None None None None
Button state:
Class originated from: 25. Type: XIKeyClass
Keycodes supported: 248
Class originated from: 25. Type: XIValuatorClass
Detail for Valuator 0:
Label: Abs X
Range: 0.000000 - 44704.000000
Resolution: 200000 units/m
Mode: absolute
Current value: 22340.000000
Class originated from: 25. Type: XIValuatorClass
Detail for Valuator 1:
Label: Abs Y
Range: 0.000000 - 27940.000000
Resolution: 200000 units/m
Mode: absolute
Current value: 13970.000000
Class originated from: 25. Type: XIValuatorClass
Detail for Valuator 2:
Label: Abs Pressure
Range: 0.000000 - 2048.000000
Resolution: 1 units/m
Mode: absolute
Current value: 0.000000
Class originated from: 25. Type: XIValuatorClass
Detail for Valuator 3:
Label: Abs Tilt X
Range: -64.000000 - 63.000000
Resolution: 57 units/m
Mode: absolute
Current value: 0.000000
Class originated from: 25. Type: XIValuatorClass
Detail for Valuator 4:
Label: Abs Tilt Y
Range: -64.000000 - 63.000000
Resolution: 57 units/m
Mode: absolute
Current value: 0.000000
Class originated from: 25. Type: XIValuatorClass
Detail for Valuator 5:
Label: Abs Wheel
Range: -900.000000 - 899.000000
Resolution: 1 units/m
Mode: absolute
Current value: 0.000000
This is an application bug, but this workaround will make sure new versions of the driver can be used until those applications have been fixed. The option will be available in the soon-to-be-released xf86-input-wacom 0.35. The upstream commit is d958ab79d21b57141415650daac88f9369a1c861.
Edit 02/06/2017: wacom devices have 8k pressure levels now.
It’s been a busy month. Part of that is that I took a week off to go to our Burning Man regional event, which threw a serious wrench into my status updates.
Hans Verkuil now has HDMI CEC working, and is polishing the patches up for inclusion in the kernel. Unfortunatelly we set his work back a bit with Boris’s new HDMI power management code, and that’s getting resolved now. He also tripped over a bug in my new dma-buf reservation code that I helped track down.
Boris has the transposer working and has reviewed the core writeback code, so hopefully we can land it soon. I’m really excited to use this for testing tiled display support (see below).
My work for the last couple of weeks has been in figuring out what to do about the fact that the new Raspbian display stack (vc4 firmwarekms, glamor, compton compositor) takes way more memory than the old display stack (fbdev on the firmware, no glamor, no compositing). It’s been pretty easy for users to hit the 256MB CMA limit, and we aren’t even using 256MB of CMA on the Pi0/1 due to its only having 512MB of system memory.
One of the ideas would be to page GPU allocations out to system memory. That only gets us from 256MB to <1GB of memory available. It’s not like you want to be swapping to SD cards. If we’re hitting 256MB this easily, we need to figure out how to fix that.
The first step was to figure out where our memory was going. I wrote a hack that had the kernel give names to the BOs it allocated, and added a new UAPI that let userspace attach more descriptive names to BOs. With that, I added a little hack to Mesa to attach some descriptions. I then made /debug/dri/0/bo_stats print out the stats on count/size per name, rather than just total. Here’s the output of LXDE with compton as I was dragging a terminal around:
scanout resource 1920x1080@32/0: 48600kb BOs (6)
tiling shadow 1920x1080: 32640kb BOs (4)
overflow: 16384kb BOs (1)
resource 1920x1080@32/0: 16320kb BOs (2)
resource 1024x1024@32/0: 4096kb BOs (1)
tiling shadow 661x411: 2184kb BOs (2)
resource 657x386@32/0: 1092kb BOs (1)
scanout resource 661x411@32/0: 1068kb BOs (1)
resource 1048576x1@8/0: 1024kb BOs (1)
resource 1024x1024@8/0: 1024kb BOs (1)
resource: 888kb BOs (20)
tiling shadow 1920x26: 240kb BOs (1)
resource 1920x26@32/0: 240kb BOs (1)
shader: 236kb BOs (56)
scanout resource 1920x26@32/0: 196kb BOs (1)
mesa cache: 152kb BOs (5)
resource 659x20@32/0: 84kb BOs (1)
resource 65536x1@8/0: 64kb BOs (1)
resource 128x128@32/0: 64kb BOs (1)
resource 1x1@32/0: 56kb BOs (14)
dumb 64x64@32: 48kb BOs (3)
resource 659x1@32/0: 36kb BOs (3)
cache: 28kb BOs (4)
RCL: 20kb BOs (2)
resource 26x1@32/0: 16kb BOs (4)
resource 1x386@32/0: 16kb BOs (2)
resource 1x361@32/0: 16kb BOs (2)
resource 1x25@32/0: 16kb BOs (4)
resource 609x1@32/0: 12kb BOs (1)
resource 607x1@32/0: 12kb BOs (1)
resource 12x18@32/0: 4kb BOs (1)
BCL: 4kb BOs (1)
This horrifying. First, this is already after a fix I’ve landed that kept us from leaking an extra overflow BO, that cost 16MB at all times. Next, 6 full-screen scanout resources? I expected 3, certainly, due to compton’s pageflipping (though for a compositor, keeping 3 is bad: I should have GPU idle time built into my pipeline anyway, as presumably GPU work is being done by other clients to generate the frames I’m compositing). Our non-pageflipping scanout buffer is probably another one (can we free the screen pixmap’s contents during pageflipping? That would sure be nice). Maybe the file manager is drawing into a window rather than the root window, to make the another one. There’s still one more I haven’t accounted for, though.
More embarassing is the tiling shadow allocations. We do this in vc4 because it can’t texture from linear BOs, so we allocate a shadow resource that we blit a tiled copy into. The cost of those tile blits are actually why we’re running a compositor in Raspbian in the first place, because window movement is too expensive otherwise.
My crazy idea was to make a new mode for glamor that just keeps all pixmaps in system memory until they need to be on the GPU (because they’re either scanned out by the GPU or they have an exposed reference to them for DRI). My previous reworks for linear vs tiled buffers in glamor already made this look easy. You end up with software fallbacks all the time (The old fbturbo driver was all software fallbacks, though), and with the new gbm_bo_map() interface we should be able to keep the cost of software fallbacks down to just the cost of the rendering performed, not a 1920x1080 readback per drawing operation.
However, 20 patches in and without having gotten to the point of gbm_bo_map() yet, this is looking like a mess. On Friday I had breakfast with keithp and talked over what I was doing, and he convinced me to go back to an older, simpler plan: Just make all of our pixmaps tiled, so we don’t have the shadow copies at all. If we don’t have the shadow copies, then we don’t need the compositor to get window-dragging performance. At least 64MB of the allocations above would go away.
The new plan means we eat the memory bandwidth cost of scanning out from tiled, but it will be easy enough to register a timer to go make a linear copy and flip to that. We’re not the only platform that would like that, I’m sure.
I’ve now written the kernel interface and debugging it is the plan for this week.
In other news, my panel-bridge v3 is now in drm-misc-next, along with most of the associated code deletion. I also helped the team trying to integrate my PL111 code with a bug in panning support, which their current 3D stack relies on. In the process of debugging the pl111+vc4 code (a full screen X11 fallback would reallocate the BO when it shouldn’t), I added debugfs register dumping for pl111, which should be useful for other developers using the code.
I have the X Server building in Travis CI, at long last. The meson build system was critical for this, as autotools was just too slow. The other key part was switching to Docker for bundling our dependencies, since 20 autotools invocations was unreasonable, and I won’t have the time to convert those 20 things to meson. Next steps on CI are to get the X Test suite running in the meson build system (the docker image already has it present).
Finally, earlier this month I submitted my Mesa register allocation series (let the driver choose the color during graph coloring), which should be good for about a 2% performance improvement to vc4 3D.
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| June 01, 2017 | |
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With modifier support added to Mesa and gbm_gralloc, it is now possible to boot Android on iMX6 platforms using no proprietary blobs at all. This makes iMX6 one of the very few embedded SOCs that needs no blobs at all to run a full graphics stack.
Not only is that a great win for Open Source in general, but it also makes the iMX6 more attractive as a platform. A further positive point is that this lays the groundwork for the iMX8 platform, and supporting it will come much easier.
Modifiers are used to represent different properties of buffers. These properties can cover a range of different information about a buffer, for example compression and tiling.
For the case of …
With modifier support added to Mesa and gbm_gralloc, it is now possible to boot Android on iMX6 platforms using no proprietary blobs at all. This makes iMX6 one of the very few embedded SOCs that needs no blobs at all to run. Not only is that a great win for Open Source in general, but it also makes the iMX6 more attractive as a platform.
Currently the modifiers work is in the process of being upstreamed, but in the meantime it can be found here. If you'd like to test this out yourself I maintain a how-to.
Modifiers are used to represent different properties of buffers. These properties can cover a range of different information about a buffer, for example …
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| May 30, 2017 | |
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With the kernel APIs off for review, and the X RandR bits looking like they're in reasonable shape, I finally found some time to sit down and figure out how I wanted to integrate this into Vulkan.
Given that a DRM lease is represented by a DRM master file descriptor, we want to use that for all of the operations in the driver, including rendering and mode setting. Using the vulkan driver render node and the lease master node together would require passing buffer objects between the kernel contexts using even more file descriptors.
The Mesa Vulkan drivers open the device nodes while enumerating devices, not when they are created. This seems a bit early to me, but it makes sure that the devices being enumerated are actually available for use, and not just present in the system. To replace the render node fd with the lease master fd means hooking into the system early enough that the enumeration code can see the lease fd. And that means creating an instance extension as the instance gets created before devices are enumerated.
This simple instance extension provides the necessary hooks to get the lease information from the application down into the driver before the DRM node is opened. In the first implementation, I added a function that could be called before the devices were enumerated to save the information in the Vulkan loader. That worked, but required quite a bit of study of the Vulkan loader and its XML description of the full Vulkan API.
Mark Young suggested that a simpler plan would be to chain the information into the VkInstanceCreateInfo pNext field; with no new APIs added to Vulkan, there shouldn't be any need to change the Vulkan loader -- the device driver would advertise the new instance extension and the application could find it.
That would have worked great, except the Vulkan loader 'helpfully' elides all instance extensions it doesn't know about before returning the list to the application. I'd say this was a bug and should be fixed, but for now, I've gone ahead and added the few necessary definitions to the loader to make it work.
In the application, it's a simple matter of searching for this extension, constructing the VkKmsDisplayInfoKEITHP structure, chaining that into the VkInstanceCreateInfo pNext list and passing that in to the vkCreateInstance call.
typedef struct VkKmsDisplayInfoKEITHP {
VkStructureType sType; /* VK_STRUCTURE_TYPE_KMS_DISPLAY_INFO_KEITHP */
const void* pNext;
int fd;
uint32_t crtc_id;
uint32_t *connector_ids;
int connector_count;
drmModeModeInfoPtr mode;
} VkKmsDisplayInfoKEITHP;
As you can see, this includes the master file descriptor along with all of the information necessary to set the desired video mode using the specified resources.
The driver just walks the pNext list from the VkInstanceCreateInfo structure looking for any provided VkKmsDisplayInfoKEITHP structure and pulls the data out.
To avoid questions about file descriptor lifetimes, the driver dup's the provided fd. The application is expected to close their copy at a suitable time.
Vulkan already has an API for directly accessing the raw device, including code for exposing video modes and everything. As tempting as it may be to just go do something simpler, there's a lot to be said for using existing APIs.
This extension doesn't provide any direct APIs for acquiring display resources, relying on the VK_EXT_acquire_xlib_display extension for that part. And that takes a VkPhysicalDisplay parameter, which is only available after the device is opened, which is why I created the VK_KEITHP_kms_display extension instead of just using the VK_EXT_acquire_xlib_display extension -- we can't increase the capabilities of the render node opened by the driver, and we don't want to keep two file descriptors around.
With the information provided by the VK_KEITHP_kms_display extension, we can implement all of the VK_KHR_display extension APIs, including enumerating planes and modes and creating the necessary display surface. Of course, there's only one plane and one mode, so some of the implementation is pretty simplistic.
The big piece of work was to create the swap chain structure and associated frame buffers.
I've taken the 'cube' example from the Vulkan loader and hacked it up to use XCB to construct a DRM lease, the VK_KEITHP_kms_display extension to pass that lease into the Vulkan driver. The existing support for the VK_KHR_display extension "just worked", which was pretty satisfying.
I'm not satisfied with the mesa code at this point; there's a bunch of code in the radeon driver which should be in the vulkan WSI bits, and the vulkan WSI bits should probably not have the KMS interfaces wired in. I'll ask around and see what other Mesa developers think I should do before restructuring it further; I'll probably have to rewrite it all at least one more time before it's ready to upstream.
I'll be cleaning the code up a bit before sending it out for review, but it's already visible in my own repositories:
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| May 29, 2017 | |
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go test and tell anyone that will listen that you really hope to never have to deal with a build system for the rest of your life.go test has supported test coverage analysis: with the ‑cover option it will tell you how much of the code is being exercised by the unit tests.bats) and gather coverage data from those runs. Even better, wouldn't be neat to merge the coverage from the unit tests with the one from those program runs and have an aggregated view of the code paths exercised by both kind of testing?cover tool inserts code to increment a counter at the start of each basic block, a different counter for each basic block of course. Some metadata is kept along side each of the counters: the location of the basic block (source file, start/end line & columns) and the size of the basic block (number of statements).go test when coverage information has been asked by the user (go test -x to see what's happening under the hood). go test then generates an instrumented test binary and runs it.go test to write out a file containing the coverage information with the ‑coverprofile option. This file starts with the coverage mode, which is how the coverage counters are incremented. This is one of set, count or atomic (see blog post for details). The rest of the file is the list of basic blocks of the program with their metadata, one block per line:github.com/clearcontainers/runtime/oci.go:241.29,244.9 3 4
go test to generate that instrumented program. It's possible to define a custom TestMain function, an entry point of a kind, for the test package. TestMain is often used to setup up the test environment before running the list of unit tests. We can hack it a bit to call our main function and jump to running our normal program instead of the tests! I ended up with something like this:cc-runtime, an OCI runtime spawning virtual machines. It definitely deserves its own blog post, but for now, knowing the binary name is enough. Generating a coverage instrumented cc-runtime binary is just a matter of invoking go test:$ go test -o cc-runtime -covermode count
go build, except it's really a test binary and we have access to the same command line arguments as we would otherwise. In particular, we can ask to output the coverage profile.$ ./cc-runtime -test.coverprofile=list.cov list
[ outputs the list of containers ]
list.cov. Hang on... there's a problem, nothing was generated: we din't get the usual "coverage: xx.x% of statements" at the end of a go test run and there's no list.cov in the current directory. What's going on?go1 API guarantee and has "internal only" warnings. Not. Even. Scared. Hacking up a dummy test suite and running is easy enough:FlushProfiles function at the end of the program and that program could very well be using os.Exit anywhere. I couldn't find better than having a tiny exit package implementing the equivalent of the libc atexit() function and forbid direct use of os.Exit in favour of exit.Exit(). It's even testable.calc program that can compute additions and substractions.$ calc add 4 8
12
add function only. We're going to run calc itself to cover the remaining statements. But first, let's see the unit tests code with both TestAdd and our hacked up TestMain function. I've swept the hacky bits away in a cover package.unit-tests.cov profile.$ go test -covermode count -coverprofile unit-tests.cov
PASS
coverage: 7.1% of statements
ok github.com/dlespiau/covertool/examples/calc 0.003s
add function after all. It's time for the magic. Let's compile an instrumented calc:$ go test -o calc -covermode count
calc a few times to exercise more code paths. For each run, we'll produce a coverage profile.$ ./calc -test.coverprofile=sub.cov sub 1 2
-1
$ covertool report sub.cov
coverage: 57.1% of statements
$ ./calc -test.coverprofile=error1.cov foo
expected 3 arguments, got 1
$ covertool report error1.cov
coverage: 21.4% of statements
$ ./calc -test.coverprofile=error2.cov mul 3 4
unknown operation: mul
$ covertool report error2.cov
coverage: 50.0% of statements
covertool$ covertool merge -o all.cov unit-tests.cov sub.cov error1.cov error2.cov
covertool to tell us the coverage of the aggregated profile:$ covertool report all.cov
coverage: 92.9% of statements
$ go tool cover -html=all.cov
add from the command line so that switch case is never covered. Good. Seems like everything is working as intended. |
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| May 23, 2017 | |
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Peter Hutterer: xinput list shows a "xwayland-pointer" device but not my real devices and what to do about it TLDR: If you see devices like "xwayland-pointer" show up in your xinput list output, then you are running under a Wayland compositor and debugging/configuration with xinput will not work.
For many years, the xinput tool has been a useful tool to debug configuration issues (it's not a configuration UI btw). It works by listing the various devices detected by the X server. So a typical output from xinput list under X could look like this:
Alas, xinput is scheduled to go the way of the dodo. More and more systems are running a Wayland session instead of an X session, and xinput just doesn't work there. Here's an example output from xinput list under a Wayland session:
:: whot@jelly:~> xinput list
⎡ Virtual core pointer id=2 [master pointer (3)]
⎜ ↳ Virtual core XTEST pointer id=4 [slave pointer (2)]
⎜ ↳ SynPS/2 Synaptics TouchPad id=22 [slave pointer (2)]
⎜ ↳ TPPS/2 IBM TrackPoint id=23 [slave pointer (2)]
⎜ ↳ ELAN Touchscreen id=20 [slave pointer (2)]
⎣ Virtual core keyboard id=3 [master keyboard (2)]
↳ Virtual core XTEST keyboard id=5 [slave keyboard (3)]
↳ Power Button id=6 [slave keyboard (3)]
↳ Video Bus id=7 [slave keyboard (3)]
↳ Lid Switch id=8 [slave keyboard (3)]
↳ Sleep Button id=9 [slave keyboard (3)]
↳ ThinkPad Extra Buttons id=24 [slave keyboard (3)]
As you can see, none of the physical devices are available, the only ones visible are the virtual devices created by XWayland. On a Wayland session, the X server doesn't have access to the physical devices. Instead, it talks via the Wayland protocol to the compositor. This image from the Wayland documentation shows the architecture:
$ xinput list
⎡ Virtual core pointer id=2 [master pointer (3)]
⎜ ↳ Virtual core XTEST pointer id=4 [slave pointer (2)]
⎜ ↳ xwayland-pointer:13 id=6 [slave pointer (2)]
⎜ ↳ xwayland-relative-pointer:13 id=7 [slave pointer (2)]
⎣ Virtual core keyboard id=3 [master keyboard (2)]
↳ Virtual core XTEST keyboard id=5 [slave keyboard (3)]
↳ xwayland-keyboard:13 id=8 [slave keyboard (3)]
This usually doesn't matter, but when it comes to debugging or configuring devices with xinput we run into a few issues. First, configuration via xinput usually means changing driver-specific properties but in the XWayland case there is no driver involved - it's all handled by libinput inside the compositor. Second, debugging via xinput only shows what the wayland protocol sends to XWayland and what XWayland then passes on to the client. For low-level issues with devices, this is all but useless.
The takeaway here is that if you see devices like "xwayland-pointer" show up in your xinput list output, then you are running under a Wayland compositor and debugging with xinput will not work. If you're trying to configure a device, use the compositor's configuration system (e.g. gsettings). If you are debugging a device, use libinput-debug-events. Or compare the behaviour between the Wayland session and the X session to narrow down where the failure point is.
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| May 20, 2017 | |
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Not only, but to a large extent I worked in the last few months on foundational improvements to KWin’s DRM backend, which is a central building block of KWin’s Wayland session. The idea in the beginninng was to directly expand upon my past Atomic Mode Setting (AMS) work from last year. We’re talking about direct scanout of graphic buffers for fullscreen applications and later layered compositing. Indeed this was my Season of KDE project with Martin Flöser as my mentor, but in the end relative to the initial goal it was unsuccessful.
The reason for the missed goal wasn’t a lack of work or enthusiasm from my side, but the realization that I need to go back and first rework the foundations, which were in some kind of disarray, mostly because of mistakes I did when I first worked on AMS last year, partly because of changes Daniel Stone made to his work-in-progress patches for AMS support in Weston, which I used as an example throughout my work on AMS in KWin, and also because of some small flaws introduced to our DRM backend before I started working on it.
The result of this rework are three seperate patches depending on each other and all of them got merged last week. They will be part of the 5.10 release. The reason for doing three patches instead of only one, was to ease the review process.
The first patch dealt with the query of important kernel display objects, which represent real hardware, the CRTCs and Connectors. KWin didn’t remember these objects in the past, although they are static while the system is running. This meant for example that KWin requeried all of them on a hot plugging event and had no prolonged knowledge about their state after a display was disconnected again. The last point made it in particular difficult to do a proper cleanup of the associated memory after a disconnect. So changing this in a way that the kernel objects are only queried once in the beginning made sense. Also from my past work I already had created a generic class for kernel object with the necessary subclasses, which could be used in this context. But still to me this patch was the most “controversial” one of the three, which means it was the one I was most worried about being somehow “wrong”, not just in details, but in general, especially since it didn’t solve any observable specific misbehaviour, which it could be benchmarked against. Of course I did my research, but there is always the anxiety of overlooking something crucial. Too bad the other patches depended on it. But the patch was accepted and to my relief everything seems to work well on the current master and the beta branch for the upcoming release as well.
The second patch restructured the DrmBuffer class. We support KWin builds with or without Generic Buffer Manager (GBM). It made therefore sense to split off the GBM dependent part of DrmBuffer into a seperate file, which gets only included when GBM is available. Martin had this idea and, although the patch is still quite large because of all the moved around code and renamed classes, the change was straight forward. I still managed to introduce a build breaking regression, which was quickly discovered and easily to solve. This patch was also meant as a preperation for the future direct scanout of buffers, which will then be done by a new subclass of DrmBuffer, also depending on GBM.
The last patch finally directly tackled all the issues I experienced when trying to use the before that rather underwhelming code path for AMS. Yes, you saw the picture on the screen, the buffer flipping worked, but basic functionality like hot plugging or display suspending were not working at all or led to unpredictable behaviour. Basically a complete rewrite later with many, many manual in and out pluggings of external monitors to test the bahaviour the problems have been solved to the point I consider the AMS code path now to be ready for daily use. For Plasma 5.11 I therefore plan to make it the new default. That means that it will be available on Intel graphics automatically from Linux kernel 4.12 onwards, when on the kernel side the Intel driver also defaults to it. If you want to test my code on Plasma 5.10 you need to set the environment variable KWIN_DRM_AMS and on kernels older than 4.12 you need to add the boot parameter i915.nuclear_pageflip. If you use Nvidia with the open source Nouveau driver, AMS should be available to you since kernel 4.10. In this case you should only need to set the environment variable above on 5.10, if you want to test it. Since I only tested AMS with Intel graphics until now, some reports back how it works with Nouveau would be great.
That’s it for now. But of course there is more to come. I haven’t given up on the direct scanout and at some point in the future I want to finish it. I already had a working prototype and mainly waited for my three patches to land. But for now I’ll postpone further work on direct scanout and layered compositing. Instead the last weeks I worked on something special for our Wayland session in 5.11. I call it Night Color, and with this name you can probably guess what it will be. And did I mention, that I was accepted as a Google Summer of Code student for the X.org foundation with my project to implement multi buffered present support in XWayland? Nah, I didn’t. Sorry for rhetorical asking in this smug way, but I’m just very happy and also a bit proud of having learned so much in basically only one year to the point of now being able to start work on an X.org project directly. I’ll write about it in another blog post in the near future.
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| May 19, 2017 | |
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| May 14, 2017 | |
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Early last year, Oracle announced it would be shutting down the general project hosting on java.net & kenai.com at the end of April 2017.
We'd been hosting various Solaris content on there since opensolaris.org shut down in 2013, and have worked to move most of it off now. We've requested some redirects be put in place where possible, but they only offer one per subproject, so we can't make all pages redirect to the best spot for that particular content.
If you referenced anything under http://solaris.java.net or its sub projects, here's a guide to where to find that content now:
And of course, much of it was archived in the Internet Archive for historical reference.
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| May 09, 2017 | |
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I’ve been procrastinating on writing up status, so this update’s a big one.
Boris Brezillon has been hacking away at implementing the VC4 transposer module as a DRM writeback connector, and has things running in test apps. My immediate goal with his work is to enable IGT testing of VC4’s HVS (hardware compositor) features, so that we can implement plane tiling and formats with confidence. However, there’s also a long term goal to extend X11’s modesetting driver to do Present into DRM planes, and only collapse planes down to the primary framebuffer once an atomic check fails or the display goes idle. This is something that other compositors like Raspberry Pi’s DispmanX firmware, Android HWC2, or Weston can all do, so we should fix X11 to do it as well.
Hans Verkuil has started on a CEC implementation for vc4’s HDMI module. The hardware looks fairly simple – unlike many other HDMI CEC implementations, ours is right there in the HDMI module, so there are no complicated inter-kernel-module dependencies to implement. I’ve set him up with register definitions and answered some hardware questions, and I suspect he’ll have results soon.
On my end, I’m excited to announce that the ARM pl111 module DRM KMS driver for Broadcom’s Cygnus is now merged to drm-misc-next, along with V3D support. This has been a more or less pleasant process: I got useful review feedback from Linus Walleij (who’s being involved in the fbdev version of this driver), some cleanups on the V3D code from Florian, and I got the code landed in a reasonable amount of time. The drm-misc process may not be perfect, but it’s the best I’ve experienced in the Linux kernel yet.
Next steps on Cygnus: I need to land a reset controller driver and the associated DT (right now if you lock up the GPU, it never resets). On Raspberry Pi reset works by us turning the power domain off and on, which causes the firmware to go through the reset process, but on Cygnus we don’t have a separate power domain for V3D. I also need to finish the panel driver and submit it (I’m using a stub for now, and have a proper panel driver in progress). And I’m working on using gallium’s “renderonly” helper functions to allow you to bring up GBM with GL accelerated on vc4 on a pl111 DRM node. This should get X, glmark, and kmscube (and any other GBM applications), working on Cygnus with no userspace changes.
I’ve also been reworking Raspberry Pi’s DSI panel support. I got really discouraged on this after trying to submit to the DRM panel tree back in December. Based on that feedback, I’m moving most of the code to a DRM bridge driver, with just the panel timing in the DRM panel tree. However, writing drivers that talk to DRM panels sucks, so I’ve written the “panel-bridge” helper that cuts about 100 lines of boilerplate from most DRM drivers that talk to a panel, by wrapping the panel in a DRM bridge structure. I submitted an early version for review last week, which was met with some skepticism. I need to re-submit my updated version that converts more drivers – probably when the patch series removes 400 lines of code from DRM, it’ll get a warmer reception.
I’ve also been working on cleaning up our GLES2 conformance test results. I’ve landed 4 patches to the GLSL compiler, and one more Mesa patch is in the queue. The most interesting problem for conformance is that some of the GLES2 conformance tests fail in our register allocator: vc4 can’t spill registers, so we need to be really good at register allocation to make arbitrary programs render successfully.
My current goal for allocation is to implement Sethi-Ullman based instruction scheduling at the QIR stage to try to keep register pressure down. However, register pressure is weighted at a middle level in the QIR instruction scheduler’s heuristics, because otherwise later on we end up too constrained for the QPU instruction scheduler and introduce stalls. To fix the QPU scheduling, I wrote a patch series that gives the driver a chance to choose among available registers during register coloring. With that, the driver can prioritize the accumulators while rotating through the available registers. Initial performance results look excellent, so I should be able to bump register pressure up in priority next and do the Sethi-Ullman work. Interestingly, this callback could resolve a longstanding issue that Intel’s pre-Sandybridge driver had in register allocation as well!
In the X Server, I’ve landed the meson build system. I’m not quite dogfooding it yet, because I can successfully run my desktop with startx but not with gdm (it looks like something is going wrong in the systemd integration). I’ve received patches from a few other X developers fixing up the meson build system for themselves, so I think we’re on track toward general adoption. I’ve made some more progress on implementing Travis CI for the X Server now, and on integrating the current X Server unit tests into meson.
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| May 05, 2017 | |
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| May 04, 2017 | |
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| April 26, 2017 | |
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Since the hardware very much matters this is going to be divided into a few parts, the common steps and the hardware specific ones.
This post is a bit of a living document and will be changed over time, and if you have any questions about it, please reach out through email (robert.foss at collabora.com) or irc (tomeu or robertfoss on #dri-devel on freenode).
Changelog:
2017-04-27: build_android.sh, setup_sdcard.sh: Added -b [device] support to build_android.sh and setup_sdcard.sh
2017-05-02: build_android.sh: Don't write to SD-card without -b option
2017-05-04: Switch git repo urls to shared repository
2017-05-09: Add compiler installation to apt-get
2017-05-09: Re-ordered some instructions
2017 … |
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| April 25, 2017 | |
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So we have a new job available for someone interested in joing our team and work on improving the Linux graphics stack. The focus of this job will be on GPU compute related work, but you should also expect to be spending time on improving the graphics driver stack in general. We are looking for someone at the Principal Engineer level, but I do recommend that even if you don’t feel you are quite at that level yet you should apply because to be fair the amount of people with the kind of experience we are looking for are few and far between, so in the end there is a chance we will hire two more junior developers instead if we have candidates with the right profile.
We are quite flexible on working location for this job, so for the right candidate working remotely is definitely a possibility. And of course if you are interested in joining us at one of our offices that is an option too, for instance we have existing team members working out of our Boston (USA), Brno(Czech Republic), Brisbane (Australia) and Munich (Germany) offices.
GPU Compute is rapidly growing in importance and use so this is your chance to be in the middle of it and work for what I personally think is one of the best companies in the world to work for.
So be sure to submit an application though the Red Hat hiring portal.
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| April 23, 2017 | |
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Since the hardware very much matters this is going to be divided into a few parts, the common steps and the hardware specific ones.
mkdir /opt/android
repo init -u https://android.googlesource.com/platform/manifest -b android-7.1.1_r28
cd /opt/android/.repo
git clone git://git.collabora.com/git/user/robertfoss/android_manifest.git local_manifests -b etnaviv-android
repo sync -j75
mkdir /opt/imx6_android
cp /opt/imx6_android
git clone git://git.collabora.com/git/user/robertfoss/linux.git -b imx_rdu2_v4.11-rc3
# The mkimage tool is used even if you're not
# using u-boot it as a bootloader
sudo apt install u-boot-tools
# Fetch Kconfig, bootloaders and some scripts
git clone git://git.collabora.com/git/user/robertfoss/rdu2.git .
# This will destroy all data … |
| The original simple-shm client on a Weston desktop. |
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| The proposed appearance of simple-shm, the way it is supposed to look like. |
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| This is how the proposed simple-shm looks like when the X-channel is mistaken as alpha. |
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| Mesa EGL with Wayland, and simplified X as comparison. |
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| Two rotated windows and some flowers. |
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| GLMatrix on the Wayland demo compositor. |
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| planet.fd.o | ||
planet.freedesktop.org is powered by Venus,
and the freedesktop.org community.
 
 
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