blk_queue_merge_bvec — set a merge_bvec function for queue
void blk_queue_merge_bvec (request_queue_t * q, merge_bvec_fn * mbfn);
Usually queues have static limitations on the max sectors or segments that
we can put in a request. Stacking drivers may have some settings that
are dynamic, and thus we have to query the queue whether it is ok to
add a new bio_vec to a bio at a given offset or not. If the block device
has such limitations, it needs to register a merge_bvec_fn to control
the size of bio's sent to it. Note that a block device *must* allow a
single page to be added to an empty bio. The block device driver may want
to use the bio_split function to deal with these bio's. By default
no merge_bvec_fn is defined for a queue, and only the fixed limits are
honored.