blk_stop_queue — stop a queue
|struct request_queue * q|
The Linux block layer assumes that a block driver will consume all
entries on the request queue when the request_fn strategy is called.
Often this will not happen, because of hardware limitations (queue
depth settings). If a device driver gets a 'queue full' response,
or if it simply chooses not to queue more I/O at one point, it can
call this function to prevent the request_fn from being called until
the driver has signalled it's ready to go again. This happens by calling
blk_start_queue to restart queue operations. Queue lock must be held.