Use NVD_GPU to control which DRM node to open in direct backend mode

When running in direct backend mode, we need to open the DRM node
ourselves, and the first node may not be the right one.

We will iterate through the DRM nodes looking for NVIDIA GPUs and will
use the first one found or the one identified by NVD_GPU if set.

src/direct/direct-export-buf.c

@@ -54,9 +54,44 @@ bool direct_initExporter(NVDriver *drv) {
 
     //make sure we have a drm fd
     if (drv->drmFd == -1) {
-        //TODO make this configurable
-        drv->drmFd = open("/dev/dri/renderD128", O_RDWR|O_CLOEXEC);
-        LOG("Manually opened DRM device");
+        uint8_t nvdGpu = 0;
+        char *nvdGpuStr = getenv("NVD_GPU");
+        if (nvdGpuStr != NULL) {
+            nvdGpu = atoi(nvdGpuStr);
+        }
+
+        int fd = -1;
+        uint8_t drmIdx = 128;
+        uint8_t nvIdx = 0;
+        char node[20] = {0, };
+        do {
+            snprintf(node, 20, "/dev/dri/renderD%d", drmIdx++);
+            fd = open(node, O_RDWR|O_CLOEXEC);
+            if (fd == -1) {
+                LOG("Unable to find NVIDIA GPU %d", nvdGpu);
+                return false;
+            }
+
+            char name[16] = {0};
+            struct drm_version ver = {
+                .name = name,
+                .name_len = 15
+            };
+            int ret = ioctl(fd, DRM_IOCTL_VERSION, &ver);
+            if (ret || strncmp(name, "nvidia-drm", 10)) {
+                close(fd);
+                continue;
+            }
+            if (nvIdx != nvdGpu) {
+                close(fd);
+                nvIdx++;
+                continue;
+            }
+            break;
+        } while (fd != -1);
+
+        drv->drmFd = fd;
+        LOG("Found NVIDIA GPU %d at %s", nvdGpu, node);
     } else {
         //dup it so we can close it later and not effect firefox
         drv->drmFd = dup(drv->drmFd);