blk_queue_flush (9)

void blk_queue_flush(struct request_queue * q, unsigned int flush);

q

the request queue for the device

flush

0, REQ_FLUSH or REQ_FLUSH | REQ_FUA

Tell block layer cache flush capability of q. If it supports flushing, REQ_FLUSH should be set. If it supports bypassing write cache for individual writes, REQ_FUA should be set.