va: Make libgudev dependency optional.

libgudev is a problematic dependency, particularly in sandboxed
environments, such as flatpak.

This patch implements a way to get the available VA devices using
brute-forced traverse of /dev/drm/renderD* directory. Thus usable in
those sandboxed environments.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/1027>

subprojects/gst-plugins-bad/sys/va/gstvadevice.c

@@ -24,7 +24,9 @@
 
 #include "gstvadevice.h"
 
+#if HAVE_GUDEV
 #include <gudev/gudev.h>
+#endif
 
 #define GST_CAT_DEFAULT gstva_debug
 GST_DEBUG_CATEGORY_EXTERN (gstva_debug);
@@ -62,6 +64,7 @@ compare_device_path (gconstpointer a, gconstpointer b, gpointer user_data)
   return strcmp (pa->render_device_path, pb->render_device_path);
 }
 
+#if HAVE_GUDEV
 GList *
 gst_va_device_find_devices (void)
 {
@@ -96,6 +99,31 @@ gst_va_device_find_devices (void)
 
   return devices.head;
 }
+#else
+GList *
+gst_va_device_find_devices (void)
+{
+  GstVaDisplay *dpy;
+  GQueue devices = G_QUEUE_INIT;
+  gchar path[64];
+  guint i;
+
+  for (i = 0; i < 8; i++) {
+    g_snprintf (path, sizeof (path), "/dev/dri/renderD%d", 128 + i);
+    if (!g_file_test (path, G_FILE_TEST_EXISTS))
+      continue;
+
+    if (!(dpy = gst_va_display_drm_new_from_path (path)))
+      continue;
+
+    GST_INFO ("Found VA-API device: %s", path);
+    g_queue_push_head (&devices, gst_va_device_new (dpy, path));
+  }
+
+  g_queue_sort (&devices, compare_device_path, NULL);
+  return devices.head;
+}
+#endif
 
 void
 gst_va_device_list_free (GList * devices)

subprojects/gst-plugins-bad/sys/va/meson.build

@@ -26,7 +26,7 @@ if va_option.disabled() or host_system != 'linux'
   subdir_done()
 endif
 
-libgudev_dep = dependency('gudev-1.0', required: va_option)
+libgudev_dep = dependency('gudev-1.0', required: false)
 
 if not gstva_dep.found() or not libgudev_dep.found()
   if va_option.enabled()
@@ -39,6 +39,7 @@ if libva_dep.version().version_compare('>= 1.8')
   va_sources += 'gstvaav1dec.c'
 endif
 
+cdata.set10('HAVE_GUDEV', libgudev_dep.found())
 
 driverdir = libva_dep.get_variable(pkgconfig: 'driverdir', internal: 'driverdir', default_value: '')
 if driverdir == ''