block: provide a direct_make_request helper

This helper allows reinserting a bio into a new queue without much
overhead, but requires all queue limits to be the same for the upper
and lower queues, and it does not provide any recursion preventions.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Javier González <javier@cnexlabs.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-core.c b/block/blk-core.c
index bb4fce6..96aaa3a 100644 (file)
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2244,6 +2244,40 @@ out:
 EXPORT_SYMBOL(generic_make_request);
 
 /**
+ * direct_make_request - hand a buffer directly to its device driver for I/O
+ * @bio:  The bio describing the location in memory and on the device.
+ *
+ * This function behaves like generic_make_request(), but does not protect
+ * against recursion.  Must only be used if the called driver is known
+ * to not call generic_make_request (or direct_make_request) again from
+ * its make_request function.  (Calling direct_make_request again from
+ * a workqueue is perfectly fine as that doesn't recurse).
+ */
+blk_qc_t direct_make_request(struct bio *bio)
+{
+       struct request_queue *q = bio->bi_disk->queue;
+       bool nowait = bio->bi_opf & REQ_NOWAIT;
+       blk_qc_t ret;
+
+       if (!generic_make_request_checks(bio))
+               return BLK_QC_T_NONE;
+
+       if (unlikely(blk_queue_enter(q, nowait))) {
+               if (nowait && !blk_queue_dying(q))
+                       bio->bi_status = BLK_STS_AGAIN;
+               else
+                       bio->bi_status = BLK_STS_IOERR;
+               bio_endio(bio);
+               return BLK_QC_T_NONE;
+       }
+
+       ret = q->make_request_fn(q, bio);
+       blk_queue_exit(q);
+       return ret;
+}
+EXPORT_SYMBOL_GPL(direct_make_request);
+
+/**
  * submit_bio - submit a bio to the block device layer for I/O
  * @bio: The &struct bio which describes the I/O
  *

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 7263702..eda3d25 100644 (file)
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -920,6 +920,7 @@ static inline void rq_flush_dcache_pages(struct request *rq)
 extern int blk_register_queue(struct gendisk *disk);
 extern void blk_unregister_queue(struct gendisk *disk);
 extern blk_qc_t generic_make_request(struct bio *bio);
+extern blk_qc_t direct_make_request(struct bio *bio);
 extern void blk_rq_init(struct request_queue *q, struct request *rq);
 extern void blk_init_request_from_bio(struct request *req, struct bio *bio);
 extern void blk_put_request(struct request *);