vhost-user-gpu: fix vugbm_device_init fallback

vugbm implements GBM device wrapping, udmabuf and memory fallback.
However, the fallback/detection logic is flawed, as if "/dev/udmabuf"
failed to be opened, it will not initialize vugbm and crash later.

Rework the vugbm_device_init() logic to initialize correctly in all
cases.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20210312100108.2706195-4-marcandre.lureau@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

contrib/vhost-user-gpu/vhost-user-gpu.c

@@ -1186,11 +1186,7 @@ main(int argc, char *argv[])
         exit(EXIT_FAILURE);
     }
 
-    if (g.drm_rnode_fd >= 0) {
-        if (!vugbm_device_init(&g.gdev, g.drm_rnode_fd)) {
-            g_warning("Failed to init DRM device, using fallback path");
-        }
-    }
+    vugbm_device_init(&g.gdev, g.drm_rnode_fd);
 
     if ((!!opt_socket_path + (opt_fdnum != -1)) != 1) {
         g_printerr("Please specify either --fd or --socket-path\n");

contrib/vhost-user-gpu/vugbm.c

@@ -199,55 +199,51 @@ vugbm_device_destroy(struct vugbm_device *dev)
     dev->device_destroy(dev);
 }
 
-bool
+void
 vugbm_device_init(struct vugbm_device *dev, int fd)
 {
-    dev->fd = fd;
+    assert(!dev->inited);
 
 #ifdef CONFIG_GBM
-    dev->dev = gbm_create_device(fd);
-#endif
-
-    if (0) {
-        /* nothing */
+    if (fd >= 0) {
+        dev->dev = gbm_create_device(fd);
     }
-#ifdef CONFIG_GBM
-    else if (dev->dev != NULL) {
+    if (dev->dev != NULL) {
+        dev->fd = fd;
         dev->alloc_bo = alloc_bo;
         dev->free_bo = free_bo;
         dev->get_fd = get_fd;
         dev->map_bo = map_bo;
         dev->unmap_bo = unmap_bo;
         dev->device_destroy = device_destroy;
+        dev->inited = true;
     }
 #endif
 #ifdef CONFIG_MEMFD
-    else if (g_file_test("/dev/udmabuf", G_FILE_TEST_EXISTS)) {
+    if (!dev->inited && g_file_test("/dev/udmabuf", G_FILE_TEST_EXISTS)) {
         dev->fd = open("/dev/udmabuf", O_RDWR);
-        if (dev->fd < 0) {
-            return false;
+        if (dev->fd >= 0) {
+            g_debug("Using experimental udmabuf backend");
+            dev->alloc_bo = udmabuf_alloc_bo;
+            dev->free_bo = udmabuf_free_bo;
+            dev->get_fd = udmabuf_get_fd;
+            dev->map_bo = udmabuf_map_bo;
+            dev->unmap_bo = udmabuf_unmap_bo;
+            dev->device_destroy = udmabuf_device_destroy;
+            dev->inited = true;
         }
-        g_debug("Using experimental udmabuf backend");
-        dev->alloc_bo = udmabuf_alloc_bo;
-        dev->free_bo = udmabuf_free_bo;
-        dev->get_fd = udmabuf_get_fd;
-        dev->map_bo = udmabuf_map_bo;
-        dev->unmap_bo = udmabuf_unmap_bo;
-        dev->device_destroy = udmabuf_device_destroy;
     }
 #endif
-    else {
+    if (!dev->inited) {
         g_debug("Using mem fallback");
         dev->alloc_bo = mem_alloc_bo;
         dev->free_bo = mem_free_bo;
         dev->map_bo = mem_map_bo;
         dev->unmap_bo = mem_unmap_bo;
         dev->device_destroy = mem_device_destroy;
-        return false;
+        dev->inited = true;
     }
-
-    dev->inited = true;
-    return true;
+    assert(dev->inited);
 }
 
 static bool

contrib/vhost-user-gpu/vugbm.h

@@ -54,7 +54,7 @@ struct vugbm_buffer {
     uint32_t format;
 };
 
-bool vugbm_device_init(struct vugbm_device *dev, int fd);
+void vugbm_device_init(struct vugbm_device *dev, int fd);
 void vugbm_device_destroy(struct vugbm_device *dev);
 
 bool vugbm_buffer_create(struct vugbm_buffer *buffer, struct vugbm_device *dev,