v4l2src: attempt to set the current camera format after open is called

To test if the device is actually being hold by another process or not.

subprojects/gst-plugins-good/sys/v4l2/gstv4l2src.c

@@ -1128,6 +1128,21 @@ gst_v4l2src_change_state (GstElement * element, GstStateChange transition)
         gst_v4l2_error (v4l2src, &error);
         return GST_STATE_CHANGE_FAILURE;
       }
+
+      /* the device might still busy even after open() succeds, so try also to
+         set the format, it will return an EBUSY error if the device is
+         already acquired by another process */
+      GstCaps *caps = gst_v4l2_object_get_caps (obj, NULL);
+      caps = gst_caps_make_writable (caps);
+      gboolean set_format = gst_v4l2src_set_format (v4l2src, caps, &error);
+      gst_caps_unref (caps);
+
+      if (!set_format) {
+        gst_v4l2_error (v4l2src, &error);
+        gst_v4l2_object_close (obj);
+        return GST_STATE_CHANGE_FAILURE;
+      }
+
       break;
     default:
       break;