[PATCH] glx/dri3: Provide error diagnostics when DRI3 allocation fails

[Keith Packard]

Instead of just segfaulting in the driver when a buffer allocation fails,
report error messages indicating what went wrong so that we can debug things.

As a simple example, chromium wraps Mesa in a sandbox which doesn't allow
access to most syscalls, including the ability to create shared memory
segments for fences. Before, you'd get a simple segfault in mesa and your 3D
acceleration would fail. Now you get:

$ chromium --disable-gpu-blacklist
[10618:10643:0930/200525:ERROR:nss_util.cc(856)] After loading Root Certs, loaded==false: NSS error code: -8018
libGL: pci id for fd 12: 8086:0a16, driver i965
libGL: OpenDriver: trying /local-miki/src/mesa/mesa/lib/i965_dri.so
libGL: Can't open configuration file /home/keithp/.drirc: Operation not permitted.
libGL: Can't open configuration file /home/keithp/.drirc: Operation not permitted.
libGL error: DRI3 Fence object allocation failure Operation not permitted
[10618:10618:0930/200525:ERROR:command_buffer_proxy_impl.cc(153)] Could not send GpuCommandBufferMsg_Initialize.
[10618:10618:0930/200525:ERROR:webgraphicscontext3d_command_buffer_impl.cc(236)] CommandBufferProxy::Initialize failed.
[10618:10618:0930/200525:ERROR:webgraphicscontext3d_command_buffer_impl.cc(256)] Failed to initialize command buffer.

This made it pretty easy to diagnose the problem in the referenced bug report.

Bugzilla: https://code.google.com/p/chromium/issues/detail?id=415681
Signed-off-by: Keith Packard <keithp at keithp.com>
---
 src/glx/dri3_glx.c | 33 +++++++++++++++++++++++++--------
 1 file changed, 25 insertions(+), 8 deletions(-)

diff --git a/src/glx/dri3_glx.c b/src/glx/dri3_glx.c
index 753b8d8..5cae50e 100644
--- a/src/glx/dri3_glx.c
+++ b/src/glx/dri3_glx.c
@@ -816,11 +816,15 @@ dri3_alloc_render_buffer(struct glx_screen *glx_screen, Drawable draw,
     */
 
    fence_fd = xshmfence_alloc_shm();
-   if (fence_fd < 0)
+   if (fence_fd < 0) {
+      ErrorMessageF("DRI3 Fence object allocation failure %s\n", strerror(errno));
       return NULL;
+   }
    shm_fence = xshmfence_map_shm(fence_fd);
-   if (shm_fence == NULL)
+   if (shm_fence == NULL) {
+      ErrorMessageF("DRI3 Fence object map failure %s\n", strerror(errno));
       goto no_shm_fence;
+   }
 
    /* Allocate the image from the driver
     */
@@ -829,8 +833,10 @@ dri3_alloc_render_buffer(struct glx_screen *glx_screen, Drawable draw,
       goto no_buffer;
 
    buffer->cpp = dri3_cpp_for_format(format);
-   if (!buffer->cpp)
+   if (!buffer->cpp) {
+      ErrorMessageF("DRI3 buffer format %d invalid\n", format);
       goto no_image;
+   }
 
    if (!psc->is_different_gpu) {
       buffer->image = (*psc->image->createImage) (psc->driScreen,
@@ -841,8 +847,10 @@ dri3_alloc_render_buffer(struct glx_screen *glx_screen, Drawable draw,
                                                   buffer);
       pixmap_buffer = buffer->image;
 
-      if (!buffer->image)
+      if (!buffer->image) {
+         ErrorMessageF("DRI3 other gpu image creation failure\n");
          goto no_image;
+      }
    } else {
       buffer->image = (*psc->image->createImage) (psc->driScreen,
                                                   width, height,
@@ -850,8 +858,10 @@ dri3_alloc_render_buffer(struct glx_screen *glx_screen, Drawable draw,
                                                   0,
                                                   buffer);
 
-      if (!buffer->image)
+      if (!buffer->image) {
+         ErrorMessageF("DRI3 gpu image creation failure\n");
          goto no_image;
+      }
 
       buffer->linear_buffer = (*psc->image->createImage) (psc->driScreen,
                                                           width, height,
@@ -861,19 +871,25 @@ dri3_alloc_render_buffer(struct glx_screen *glx_screen, Drawable draw,
                                                           buffer);
       pixmap_buffer = buffer->linear_buffer;
 
-      if (!buffer->linear_buffer)
+      if (!buffer->linear_buffer) {
+         ErrorMessageF("DRI3 gpu linear image creation failure\n");
          goto no_linear_buffer;
+      }
    }
 
    /* X wants the stride, so ask the image for it
     */
-   if (!(*psc->image->queryImage)(pixmap_buffer, __DRI_IMAGE_ATTRIB_STRIDE, &stride))
+   if (!(*psc->image->queryImage)(pixmap_buffer, __DRI_IMAGE_ATTRIB_STRIDE, &stride)) {
+      ErrorMessageF("DRI3 get image stride failed\n");
       goto no_buffer_attrib;
+   }
 
    buffer->pitch = stride;
 
-   if (!(*psc->image->queryImage)(pixmap_buffer, __DRI_IMAGE_ATTRIB_FD, &buffer_fd))
+   if (!(*psc->image->queryImage)(pixmap_buffer, __DRI_IMAGE_ATTRIB_FD, &buffer_fd)) {
+      ErrorMessageF("DRI3 get image FD failed\n");
       goto no_buffer_attrib;
+   }
 
    xcb_dri3_pixmap_from_buffer(c,
                                (pixmap = xcb_generate_id(c)),
@@ -913,6 +929,7 @@ no_buffer:
    xshmfence_unmap_shm(shm_fence);
 no_shm_fence:
    close(fence_fd);
+   ErrorMessageF("DRI3 alloc_render_buffer failed\n");
    return NULL;
 }
 
-- 
2.1.1