[PATCH libdrm] libdrm: Allow dynamic drm majors on linux

[Thomas Hellstrom]

To determine whether a device node is a drm device node or not, the code
currently compares the node's major number to the static drm major device
number.

This breaks the standalone vmwgfx driver on XWayland dri clients,
https://cgit.freedesktop.org/mesa/vmwgfx
and any future attempt to introduce dynamic device numbers for drm.

So instead of checking for the device major, instead check for the presence
of the /sys/dev/char/<major>:<minor>/device/drm directory.

Signed-off-by: Thomas Hellstrom <thellstrom at vmware.com>
---
 xf86drm.c | 31 +++++++++++++++++++++++--------
 1 file changed, 23 insertions(+), 8 deletions(-)

diff --git a/xf86drm.c b/xf86drm.c
index 7807dce9..4cfc5d3e 100644
--- a/xf86drm.c
+++ b/xf86drm.c
@@ -2761,6 +2761,21 @@ char *drmGetDeviceNameFromFd(int fd)
     return strdup(name);
 }
 
+static bool
+drmNodeIsDRM(int maj, int min)
+{
+#ifdef __linux__
+  char path[64];
+  struct stat sbuf;
+
+  snprintf(path, sizeof(path), "/sys/dev/char/%d:%d/device/drm",
+	   maj, min);
+  return stat(path, &sbuf) == 0;
+#else
+  return maj == DRM_MAJOR;
+#endif
+}
+
 int drmGetNodeTypeFromFd(int fd)
 {
     struct stat sbuf;
@@ -2772,7 +2787,7 @@ int drmGetNodeTypeFromFd(int fd)
     maj = major(sbuf.st_rdev);
     min = minor(sbuf.st_rdev);
 
-    if (maj != DRM_MAJOR || !S_ISCHR(sbuf.st_mode)) {
+    if (!drmNodeIsDRM(maj, min) || !S_ISCHR(sbuf.st_mode)) {
         errno = EINVAL;
         return -1;
     }
@@ -2837,7 +2852,7 @@ static char *drmGetMinorNameForFD(int fd, int type)
     maj = major(sbuf.st_rdev);
     min = minor(sbuf.st_rdev);
 
-    if (maj != DRM_MAJOR || !S_ISCHR(sbuf.st_mode))
+    if (!drmNodeIsDRM(maj, min) || !S_ISCHR(sbuf.st_mode))
         return NULL;
 
     snprintf(buf, sizeof(buf), "/sys/dev/char/%d:%d/device/drm", maj, min);
@@ -2871,7 +2886,7 @@ static char *drmGetMinorNameForFD(int fd, int type)
     maj = major(sbuf.st_rdev);
     min = minor(sbuf.st_rdev);
 
-    if (maj != DRM_MAJOR || !S_ISCHR(sbuf.st_mode))
+    if (!drmNodeIsDRM(maj, min) || !S_ISCHR(sbuf.st_mode))
         return NULL;
 
     switch (type) {
@@ -3731,7 +3746,7 @@ process_device(drmDevicePtr *device, const char *d_name,
     maj = major(sbuf.st_rdev);
     min = minor(sbuf.st_rdev);
 
-    if (maj != DRM_MAJOR || !S_ISCHR(sbuf.st_mode))
+    if (!drmNodeIsDRM(maj, min) || !S_ISCHR(sbuf.st_mode))
         return -1;
 
     subsystem_type = drmParseSubsystemType(maj, min);
@@ -3845,7 +3860,7 @@ int drmGetDevice2(int fd, uint32_t flags, drmDevicePtr *device)
     maj = major(sbuf.st_rdev);
     min = minor(sbuf.st_rdev);
 
-    if (maj != DRM_MAJOR || !S_ISCHR(sbuf.st_mode))
+    if (!drmNodeIsDRM(maj, min) || !S_ISCHR(sbuf.st_mode))
         return -EINVAL;
 
     node_type = drmGetMinorType(min);
@@ -3911,7 +3926,7 @@ int drmGetDevice2(int fd, uint32_t flags, drmDevicePtr *device)
     maj = major(sbuf.st_rdev);
     min = minor(sbuf.st_rdev);
 
-    if (maj != DRM_MAJOR || !S_ISCHR(sbuf.st_mode))
+    if (!drmNodeIsDRM(maj, min) || !S_ISCHR(sbuf.st_mode))
         return -EINVAL;
 
     subsystem_type = drmParseSubsystemType(maj, min);
@@ -4071,7 +4086,7 @@ char *drmGetDeviceNameFromFd2(int fd)
     maj = major(sbuf.st_rdev);
     min = minor(sbuf.st_rdev);
 
-    if (maj != DRM_MAJOR || !S_ISCHR(sbuf.st_mode))
+    if (!drmNodeIsDRM(maj, min) || !S_ISCHR(sbuf.st_mode))
         return NULL;
 
     snprintf(path, sizeof(path), "/sys/dev/char/%d:%d", maj, min);
@@ -4097,7 +4112,7 @@ char *drmGetDeviceNameFromFd2(int fd)
     maj = major(sbuf.st_rdev);
     min = minor(sbuf.st_rdev);
 
-    if (maj != DRM_MAJOR || !S_ISCHR(sbuf.st_mode))
+    if (!drmNodeIsDRM(maj, min) || !S_ISCHR(sbuf.st_mode))
         return NULL;
 
     node_type = drmGetMinorType(min);
-- 
2.18.0.rc1