Mesa (main): loader: Avoid enumerating drm devices just to get an fd's PCI ID.

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Module: Mesa
Branch: main
Commit: f839b9599f863fa5bb1a6a6c24bbb621b7a1b4c9
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=f839b9599f863fa5bb1a6a6c24bbb621b7a1b4c9

Author: Emma Anholt <emma at anholt.net>
Date:   Tue Oct 12 14:31:31 2021 -0700

loader: Avoid enumerating drm devices just to get an fd's PCI ID.

Cuts 1/3 of the runtime of the VA-API unit tests (which do a separate
pipe-loader init per test) on radeonsi on my system by not faffing around
in sysfs so much.

Reviewed-by: Adam Jackson <ajax at redhat.com>
Reviewed-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer at amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13324>

---

 src/loader/loader.c | 43 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/src/loader/loader.c b/src/loader/loader.c
index 58727155075..945c99fb4bf 100644
--- a/src/loader/loader.c
+++ b/src/loader/loader.c
@@ -47,6 +47,7 @@
 #include <GL/gl.h>
 #include <GL/internal/dri_interface.h>
 #include "loader.h"
+#include "util/os_file.h"
 
 #ifdef HAVE_LIBDRM
 #include <xf86drm.h>
@@ -407,10 +408,52 @@ drm_get_pci_id_for_fd(int fd, int *vendor_id, int *chip_id)
 }
 #endif
 
+#ifdef __linux__
+static int loader_get_linux_pci_field(int maj, int min, const char *field)
+{
+   char path[PATH_MAX + 1];
+   snprintf(path, sizeof(path), "/sys/dev/char/%d:%d/device/%s", maj, min, field);
+
+   char *field_str = os_read_file(path, NULL);
+   if (!field_str) {
+      /* Probably non-PCI device. */
+      return 0;
+   }
+
+   int value = (int)strtoll(field_str, NULL, 16);
+   free(field_str);
+
+   return value;
+}
+
+static bool
+loader_get_linux_pci_id_for_fd(int fd, int *vendor_id, int *chip_id)
+{
+   struct stat sbuf;
+   if (fstat(fd, &sbuf) != 0) {
+      log_(_LOADER_DEBUG, "MESA-LOADER: failed to fstat fd\n");
+      return false;
+   }
+
+   int maj = major(sbuf.st_rdev);
+   int min = minor(sbuf.st_rdev);
+
+   *vendor_id = loader_get_linux_pci_field(maj, min, "vendor");
+   *chip_id = loader_get_linux_pci_field(maj, min, "device");
+
+   return *vendor_id && *chip_id;
+}
+#endif /* __linux__ */
 
 bool
 loader_get_pci_id_for_fd(int fd, int *vendor_id, int *chip_id)
 {
+#ifdef __linux__
+   /* Implementation without causing full enumeration of DRM devices. */
+   if (loader_get_linux_pci_id_for_fd(fd, vendor_id, chip_id))
+      return true;
+#endif
+
 #if HAVE_LIBDRM
    return drm_get_pci_id_for_fd(fd, vendor_id, chip_id);
 #endif