+ /* This code path is a replacement for the BKL. It is a major
+ * hack but it will have to do for those drivers that are not
+ * yet converted to use unlocked_ioctl.
+ *
+ * There are two options: if the driver implements struct
+ * v4l2_device, then the lock defined there is used to
+ * serialize the ioctls. Otherwise the v4l2 core lock defined
+ * below is used. This lock is really bad since it serializes
+ * completely independent devices.
+ *
+ * Both variants suffer from the same problem: if the driver
+ * sleeps, then it blocks all ioctls since the lock is still
+ * held. This is very common for VIDIOC_DQBUF since that
+ * normally waits for a frame to arrive. As a result any other
+ * ioctl calls will proceed very, very slowly since each call
+ * will have to wait for the VIDIOC_QBUF to finish. Things that
+ * should take 0.01s may now take 10-20 seconds.
+ *
+ * The workaround is to *not* take the lock for VIDIOC_DQBUF.
+ * This actually works OK for videobuf-based drivers, since
+ * videobuf will take its own internal lock.
+ */