Man page 9 : blk_fetch_request

blk_fetch_request - fetch a request from a request queue

struct request * blk_fetch_request(struct request_queue *  q );

q
    request queue to fetch a request from

Return the request at the top of q. The request is started on return and LLD can start processing it immediately.

Pointer to the request at the top of q if available. Null otherwise.

queue_lock must be held.