Using apitrace with Xvfb

Fri May 15 00:03:22 PDT 2015

Hello.

I wanted to record and replay a trace on a headless server for regression
testing purposes. The headless server does not have an X session so the
plan was to create one with Xvfb.

Something like:

    % Xvfb :99 -screen 0 640x480x24 &
    % DISPLAY=:99 apitrace trace -o trace /path/to/executable
    % DISPLAY=:99 apitrace replay trace

While replaying the trace I'd capture the frame checksums and check against
the golden copy and that'd confirm the tests.

When I try this with apitrace the third step (replay) fails with the error
message:

    error: failed to create OpenGL 3.3 core context.

My test program is attached. It is a very simple program that uses freeglut
to initialise a window and then prints the GL_RENDERER, GL_VENDOR, ...
strings.

It is compiled with:

    g++ -o example example.cpp -lGL -lglut

If I run the program when an X session is active:

    % ./example
    OpenGL initialized:
      Version:  3.3 (Core Profile) Mesa 10.6.0-devel
      Vendor:   Intel Open Source Technology Center
      Renderer: Mesa DRI Intel(R) HD Graphics 5500 (Broadwell GT2)
      GLSL:     3.30

(Note: running on a broadwell laptop, so this output is entirely expected).

Running it in the Xvfb session:

    % DISPLAY=:99 ./example
    OpenGL initialized:
      Version:  3.3 (Core Profile) Mesa 10.6.0-devel
     Vendor:   VMware, Inc.
     Renderer: Gallium 0.4 on llvmpipe (LLVM 3.6, 256 bits)
     GLSL:     3.30

Running the trace I get:

    % DISPLAY=:99 apitrace trace -o trace example
    apitrace: loaded into /usr/local/bin/apitrace
    apitrace: loaded into /home/nick/example
    apitrace: tracing to trace
    apitrace: redirecting dlopen("libGL.so.1", 0x102)
    OpenGL initialized:
    apitrace: attempting to read configuration file:
/home/nick/.config/apitrace/gltrace.conf
      Version:  3.3 (Core Profile) Mesa 10.6.0-devel
      Vendor:   VMware, Inc.
      Renderer: Gallium 0.4 on llvmpipe (LLVM 3.6, 256 bits)
      GLSL:     3.30

If I use apitrace to dump the trace:

    % DISPLAY=:99 apitrace dump trace
    1 glXChooseFBConfig(dpy = 0xa444f0, screen = 0, attribList =
{GLX_RED_SIZE, 1, GLX_GREEN_SIZE, 1, GLX_BLUE_SIZE, 1, GLX_DOUBLEBUFFER,
True, GLX_DEPTH_SIZE, 1, 0}, nitems = &64) = {0xa7e020, 0xa7e200, 0xa83480,
0xa83660, 0xa7d4e0, 0xa7d6c0, 0xa82940, 0xa82b20, 0xa7da80, 0xa7dc60,
0xa82ee0, 0xa830c0, 0xa7ce10, 0xa7d120, 0xa823a0, 0xa82580, 0xa7c2d0,
0xa7c4b0, 0xa81860, 0xa81a40, 0xa7b790, 0xa7b970, 0xa80d20, 0xa80f00,
0xa7bd30, 0xa7bf10, 0xa812c0, 0xa814a0, 0xa7b1f0, 0xa7b3d0, 0xa80780,
0xa80960, 0xa7e110, 0xa7e2f0, 0xa83570, 0xa83750, 0xa7d5d0, 0xa7d7b0,
0xa82a30, 0xa82c10, 0xa7db70, 0xa7dd50, 0xa82fd0, 0xa831b0, 0xa7cf00,
0xa7d210, 0xa82490, 0xa82670, 0xa7c3c0, 0xa7c5a0, 0xa81950, 0xa81b30,
0xa7b880, 0xa7ba60, 0xa80e10, 0xa80ff0, 0xa7be20, 0xa7c000, 0xa813b0,
0xa81590, 0xa7b2e0, 0xa7b4c0, 0xa80870, 0xa80a50}
    2 glXGetVisualFromFBConfig(dpy = 0xa444f0, config = 0xa7e020) =
&{visual = 0xa4f630, visualid = 297, screen = 0, depth = 24, c_class = 4,
red_mask = 16711680, green_mask = 65280, blue_mask = 255, colormap_size =
256, bits_per_rgb = 8}
    4 glXCreateContextAttribsARB(dpy = 0xa444f0, config = 0xa7e020,
share_context = NULL, direct = True, attrib_list =
{GLX_CONTEXT_MAJOR_VERSION_ARB, 3, GLX_CONTEXT_MINOR_VERSION_ARB, 3,
GLX_CONTEXT_FLAGS_ARB, GLX_CONTEXT_DEBUG_BIT_ARB |
GLX_CONTEXT_FORWARD_COMPATIBLE_BIT_ARB, 0}) = 0xa55da0
    6 glXMakeContextCurrent(dpy = 0xa444f0, draw = 2097154, read = 2097154,
ctx = 0xa55da0) = True
    7 glViewport(x = 0, y = 0, width = 400, height = 400)
    8 glScissor(x = 0, y = 0, width = 400, height = 400)
    9 glXMakeContextCurrent(dpy = 0xa444f0, draw = 2097154, read = 2097154,
ctx = 0xa55da0) = True
    14 glXMakeContextCurrent(dpy = 0xa444f0, draw = 2097154, read =
2097154, ctx = 0xa55da0) = True
    15 glXDestroyContext(dpy = 0xa444f0, ctx = 0xa55da0)

If I try to replay:

    %DISPLAY=:99 apitrace replay -vvv trace
    0 @0 glXQueryExtension(dpy = 0xa444f0, errorb = NULL, event = NULL) =
True
    1 @0 glXChooseFBConfig(dpy = 0xa444f0, screen = 0, attribList =
{GLX_RED_SIZE, 1, GLX_GREEN_SIZE, 1, GLX_BLUE_SIZE, 1, GLX_DOUBLEBUFFER,
True, GLX_DEPTH_SIZE, 1, 0}, nitems = &64) = {0xa7e020, 0xa7e200, 0xa83480,
0xa83660, 0xa7d4e0, 0xa7d6c0, 0xa82940, 0xa82b20, 0xa7da80, 0xa7dc60,
0xa82ee0, 0xa830c0, 0xa7ce10, 0xa7d120, 0xa823a0, 0xa82580, 0xa7c2d0,
0xa7c4b0, 0xa81860, 0xa81a40, 0xa7b790, 0xa7b970, 0xa80d20, 0xa80f00,
0xa7bd30, 0xa7bf10, 0xa812c0, 0xa814a0, 0xa7b1f0, 0xa7b3d0, 0xa80780,
0xa80960, 0xa7e110, 0xa7e2f0, 0xa83570, 0xa83750, 0xa7d5d0, 0xa7d7b0,
0xa82a30, 0xa82c10, 0xa7db70, 0xa7dd50, 0xa82fd0, 0xa831b0, 0xa7cf00,
0xa7d210, 0xa82490, 0xa82670, 0xa7c3c0, 0xa7c5a0, 0xa81950, 0xa81b30,
0xa7b880, 0xa7ba60, 0xa80e10, 0xa80ff0, 0xa7be20, 0xa7c000, 0xa813b0,
0xa81590, 0xa7b2e0, 0xa7b4c0, 0xa80870, 0xa80a50}
    2 @0 glXGetVisualFromFBConfig(dpy = 0xa444f0, config = 0xa7e020) =
&{visual = 0xa4f630, visualid = 297, screen = 0, depth = 24, c_class = 4,
red_mask = 16711680, green_mask = 65280, blue_mask = 255, colormap_size =
256, bits_per_rgb = 8}
    3 @0 glXGetProcAddressARB(procName = "glXCreateContextAttribsARB") =
0x7f49a8ac15f2
    4 @0 glXCreateContextAttribsARB(dpy = 0xa444f0, config = 0xa7e020,
share_context = NULL, direct = True, attrib_list =
{GLX_CONTEXT_MAJOR_VERSION_ARB, 3, GLX_CONTEXT_MINOR_VERSION_ARB, 3,
GLX_CONTEXT_FLAGS_ARB, GLX_CONTEXT_DEBUG_BIT_ARB |
GLX_CONTEXT_FORWARD_COMPATIBLE_BIT_ARB, 0}) = 0xa55da0
    *error: failed to create OpenGL 3.3 core context.*

Initially I suspected that the DISPLAY variable was not propagating to the
glretrace child of "apitrace replay" but I have
 1) straced to verify that the environment variable DISPLAY=:99 is making
it through to the glretrace child process spawned by apitrace, and
 2) confirmed that the code uses XOpenDisplay(NULL), which should open the
X display in the environment variable DISPLAY

Anyone have any ideas or experience running apitrace on headless servers?

Thanks,
 -- Nick
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