tools: fix r1780 cycle prerequisites and add SDL GLX-pbuffer shim

- cycle-r1780.sh: load vfio modules one per modprobe (the multi-module
  form was silently treating the extra names as parameters and never
  loading mdev); auto-detect the vgpu mdev type and prefer the 2 GiB
  type used by the campaign.
- sdl_cap.c: gate capture-file creation to processes that can actually
  read GL pixels (a child was truncating the capture), and log the
  capture pid/pointers.
- gz_pbuf.c: LD_PRELOAD shim that gives an SDL2 GL client a GLX pbuffer
  context on the guest's NVIDIA X server (the proven gl_frames path),
  with SDL_GL_GetDrawableSize/SwapWindow interception.

1 files changed, 7 insertions, 3 deletions

diff --git a/tools/guest-diag/sdl_cap.c b/tools/guest-diag/sdl_cap.c
index 23c83ab..5b9c096 100644
--- a/tools/guest-diag/sdl_cap.c
+++ b/tools/guest-diag/sdl_cap.c
@@ -87,10 +87,12 @@ __attribute__((constructor)) static void cap_init(void)
         if (h)
             real_glReadPixels = dlsym(h, "glReadPixels");
     }
-    fprintf(stderr, "[gzcap] init path=%s present=%p updwin=%p swap=%p read=%p gros=%p\n",
-            p, (void *)real_RenderPresent, (void *)real_UpdateWindowSurface,
+    fprintf(stderr, "[gzcap] init pid=%d path=%s present=%p updwin=%p swap=%p read=%p gros=%p\n",
+            (int)getpid(), p, (void *)real_RenderPresent, (void *)real_UpdateWindowSurface,
             (void *)real_GL_SwapWindow, (void *)real_RenderReadPixels,
             (void *)real_GetRendererOutputSize, (void *)real_glReadPixels);
+    if (!real_glReadPixels && !real_RenderReadPixels)
+        return;
     cap_fp = fopen(p, "wb");
     if (!cap_fp)
         return;
@@ -192,7 +194,9 @@ void SDL_GL_SwapWindow(SDL_Window *win)
     static size_t gbufsz;
 
     if (!hit++)
-        fprintf(stderr, "[gzcap] hook GLSwapWindow\n");
+        fprintf(stderr, "[gzcap] hook GLSwapWindow pid=%d fp=%p read=%p gros=%p\n",
+                (int)getpid(), (void *)cap_fp, (void *)real_glReadPixels,
+                (void *)real_GL_GetDrawableSize);
     if (cap_fp && !cap_stop && real_glReadPixels && real_GL_GetDrawableSize) {
         int w = 0, h = 0;