+v4l2_file_operations and locking
+--------------------------------
+
+You can set a pointer to a mutex_lock in struct video_device. Usually this
+will be either a top-level mutex or a mutex per device node. If you want
+finer-grained locking then you have to set it to NULL and do you own locking.
+
+If a lock is specified then all file operations will be serialized on that
+lock. If you use videobuf then you must pass the same lock to the videobuf
+queue initialize function: if videobuf has to wait for a frame to arrive, then
+it will temporarily unlock the lock and relock it afterwards. If your driver
+also waits in the code, then you should do the same to allow other processes
+to access the device node while the first process is waiting for something.
+
+The implementation of a hotplug disconnect should also take the lock before
+calling v4l2_device_disconnect.