[03/17] block: provide a direct_make_request helper

Commit Message

Christoph Hellwig Oct. 23, 2017, 2:51 p.m. UTC

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 <[e-mail]>
Reviewed-by: Sagi Grimberg <[e-mail]>
---
 block/blk-core.c       | 34 ++++++++++++++++++++++++++++++++++
 include/linux/blkdev.h |  1 +
 2 files changed, 35 insertions(+)

Comments

Hannes Reinecke Oct. 24, 2017, 7:05 a.m. UTC | #1

On 10/23/2017 04:51 PM, Christoph Hellwig wrote:
> 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 <[e-mail]>
> Reviewed-by: Sagi Grimberg <[e-mail]>
> ---
>  block/blk-core.c       | 34 ++++++++++++++++++++++++++++++++++
>  include/linux/blkdev.h |  1 +
>  2 files changed, 35 insertions(+)
> 
Reviewed-by: Hannes Reinecke <[e-mail]>

Cheers,

Hannes

=?UTF-8?q?Javier=20Gonz=C3=A1lez?= Oct. 24, 2017, 5:57 p.m. UTC | #2

> On 23 Oct 2017, at 16.51, Christoph Hellwig <[e-mail]> wrote:
> 
> 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 <[e-mail]>
> Reviewed-by: Sagi Grimberg <[e-mail]>
> ---
> block/blk-core.c       | 34 ++++++++++++++++++++++++++++++++++
> include/linux/blkdev.h |  1 +
> 2 files changed, 35 insertions(+)
> 


Reviewed-by: Javier González <[e-mail]>

Patch

diff --git a/block/blk-core.c b/block/blk-core.c
index 14f7674fa0b1..b8c80f39f5fe 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2241,6 +2241,40 @@  blk_qc_t generic_make_request(struct bio *bio)
 }
 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 02fa42d24b52..780f01db5899 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -936,6 +936,7 @@  do {								\
 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 *);