The block layer provides a function direct_make_request - but it doesn't
provide any test whether this function may be used or not.
Device mapper currently uses a dirty trick - it compares the result of
bdevname against the string "nvme" to test if direct_make_request can be
used.
The information whether the driver will or won't recurse can be easily
obtained in generic_make_request (by comparing make_request_fn - or
alternatively, we could introduce a queue flag for this), so my suggestion
is to just delete direct_make_request and fold this "norecurse"
optimization directly into generic_make_request This will allow us to
simplify device mapper paths and get rid of device name matching.
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
---
block/blk-core.c | 60 ++++++++++++++----------------------------
block/blk-mq.c | 2 -
drivers/md/dm.c | 5 ---
drivers/nvme/host/multipath.c | 2 -
include/linux/blkdev.h | 1
5 files changed, 24 insertions(+), 46 deletions(-)
Index: linux-2.6/block/blk-core.c
===================================================================
--- linux-2.6.orig/block/blk-core.c 2018-02-26 20:37:19.088499000 +0100
+++ linux-2.6/block/blk-core.c 2018-02-26 20:43:57.839999000 +0100
@@ -2265,6 +2265,8 @@ end_io:
return false;
}
+blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio);
+
/**
* generic_make_request - hand a buffer to its device driver for I/O
* @bio: The bio describing the location in memory and on the device.
@@ -2300,10 +2302,14 @@ blk_qc_t generic_make_request(struct bio
*/
struct bio_list bio_list_on_stack[2];
blk_qc_t ret = BLK_QC_T_NONE;
+ bool may_recurse;
if (!generic_make_request_checks(bio))
goto out;
+ may_recurse = bio->bi_disk->queue->make_request_fn != blk_queue_bio &&
+ bio->bi_disk->queue->make_request_fn != blk_mq_make_request;
+
/*
* We only want one ->make_request_fn to be active at a time, else
* stack usage with stacked devices could be a problem. So use
@@ -2314,7 +2320,7 @@ blk_qc_t generic_make_request(struct bio
* it is non-NULL, then a make_request is active, and new requests
* should be added at the tail
*/
- if (current->bio_list) {
+ if (may_recurse && current->bio_list) {
bio_list_add(¤t->bio_list[0], bio);
goto out;
}
@@ -2334,8 +2340,10 @@ blk_qc_t generic_make_request(struct bio
* bio_list, and call into ->make_request() again.
*/
BUG_ON(bio->bi_next);
- bio_list_init(&bio_list_on_stack[0]);
- current->bio_list = bio_list_on_stack;
+ if (may_recurse) {
+ bio_list_init(&bio_list_on_stack[0]);
+ current->bio_list = bio_list_on_stack;
+ }
do {
struct request_queue *q = bio->bi_disk->queue;
blk_mq_req_flags_t flags = bio->bi_opf & REQ_NOWAIT ?
@@ -2345,12 +2353,17 @@ blk_qc_t generic_make_request(struct bio
struct bio_list lower, same;
/* Create a fresh bio_list for all subordinate requests */
- bio_list_on_stack[1] = bio_list_on_stack[0];
- bio_list_init(&bio_list_on_stack[0]);
+ if (may_recurse) {
+ bio_list_on_stack[1] = bio_list_on_stack[0];
+ bio_list_init(&bio_list_on_stack[0]);
+ }
ret = q->make_request_fn(q, bio);
blk_queue_exit(q);
+ if (!may_recurse)
+ goto out;
+
/* sort new bios into those for a lower level
* and those for the same level
*/
@@ -2371,6 +2384,9 @@ blk_qc_t generic_make_request(struct bio
bio_wouldblock_error(bio);
else
bio_io_error(bio);
+
+ if (!may_recurse)
+ goto out;
}
bio = bio_list_pop(&bio_list_on_stack[0]);
} while (bio);
@@ -2382,40 +2398,6 @@ 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 ? BLK_MQ_REQ_NOWAIT : 0))) {
- 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
*
Index: linux-2.6/block/blk-mq.c
===================================================================
--- linux-2.6.orig/block/blk-mq.c 2018-02-26 20:37:19.088499000 +0100
+++ linux-2.6/block/blk-mq.c 2018-02-26 20:37:19.078499000 +0100
@@ -1861,7 +1861,7 @@ blk_status_t blk_mq_request_issue_direct
return ret;
}
-static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
+blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
{
const int is_sync = op_is_sync(bio->bi_opf);
const int is_flush_fua = op_is_flush(bio->bi_opf);
Index: linux-2.6/drivers/md/dm.c
===================================================================
--- linux-2.6.orig/drivers/md/dm.c 2018-02-26 20:37:19.088499000 +0100
+++ linux-2.6/drivers/md/dm.c 2018-02-26 20:37:19.088499000 +0100
@@ -1237,10 +1237,7 @@ static blk_qc_t __map_bio(struct dm_targ
/* the bio has been remapped so dispatch it */
trace_block_bio_remap(clone->bi_disk->queue, clone,
bio_dev(io->orig_bio), sector);
- if (md->type == DM_TYPE_NVME_BIO_BASED)
- ret = direct_make_request(clone);
- else
- ret = generic_make_request(clone);
+ ret = generic_make_request(clone);
break;
case DM_MAPIO_KILL:
free_tio(tio);
Index: linux-2.6/drivers/nvme/host/multipath.c
===================================================================
--- linux-2.6.orig/drivers/nvme/host/multipath.c 2018-02-26 20:37:19.088499000 +0100
+++ linux-2.6/drivers/nvme/host/multipath.c 2018-02-26 20:37:19.088499000 +0100
@@ -89,7 +89,7 @@ static blk_qc_t nvme_ns_head_make_reques
if (likely(ns)) {
bio->bi_disk = ns->disk;
bio->bi_opf |= REQ_NVME_MPATH;
- ret = direct_make_request(bio);
+ ret = generic_make_request(bio);
} else if (!list_empty_careful(&head->list)) {
dev_warn_ratelimited(dev, "no path available - requeuing I/O\n");
Index: linux-2.6/include/linux/blkdev.h
===================================================================
--- linux-2.6.orig/include/linux/blkdev.h 2018-02-26 20:37:19.088499000 +0100
+++ linux-2.6/include/linux/blkdev.h 2018-02-26 20:37:19.088499000 +0100
@@ -1014,7 +1014,6 @@ static inline void rq_flush_dcache_pages
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 *);
--
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