[PATCH 3/5] block: add a blk_alloc_discard_bio helper

[Christoph Hellwig <hch@lst.de>]

Factor out a helper from __blkdev_issue_discard that chews off as much as
possible from a discard range and allocates a bio for it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-lib.c     | 58 ++++++++++++++++++++++++++-------------------
 include/linux/bio.h |  3 +++
 2 files changed, 37 insertions(+), 24 deletions(-)

diff --git a/block/blk-lib.c b/block/blk-lib.c
index 50923508a32466..fd97f4dd34e7f4 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -55,36 +55,46 @@ static void await_bio_chain(struct bio *bio)
 	blk_wait_io(&done);
 }
 
+struct bio *blk_alloc_discard_bio(struct block_device *bdev,
+		sector_t *sector, sector_t *nr_sects, gfp_t gfp_mask)
+{
+	sector_t bio_sects = min(*nr_sects, bio_discard_limit(bdev, *sector));
+	struct bio *bio;
+
+	if (WARN_ON_ONCE(!(gfp_mask & __GFP_RECLAIM)))
+		return NULL;
+	if (!bio_sects)
+		return NULL;
+
+	bio = bio_alloc(bdev, 0, REQ_OP_DISCARD, gfp_mask);
+	bio->bi_iter.bi_sector = *sector;
+	bio->bi_iter.bi_size = bio_sects << SECTOR_SHIFT;
+	*sector += bio_sects;
+	*nr_sects -= bio_sects;
+	/*
+	 * We can loop for a long time in here if someone does full device
+	 * discards (like mkfs).  Be nice and allow us to schedule out to avoid
+	 * softlocking if preempt is disabled.
+	 */
+	cond_resched();
+	return bio;
+}
+
 int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
 		sector_t nr_sects, gfp_t gfp_mask, struct bio **biop)
 {
-	struct bio *bio = *biop;
-
-	while (nr_sects) {
-		sector_t req_sects =
-			min(nr_sects, bio_discard_limit(bdev, sector));
+	struct bio *bio;
 
-		bio = blk_next_bio(bio, bdev, 0, REQ_OP_DISCARD, gfp_mask);
-		bio->bi_iter.bi_sector = sector;
-		bio->bi_iter.bi_size = req_sects << 9;
-		sector += req_sects;
-		nr_sects -= req_sects;
-
-		/*
-		 * We can loop for a long time in here, if someone does
-		 * full device discards (like mkfs). Be nice and allow
-		 * us to schedule out to avoid softlocking if preempt
-		 * is disabled.
-		 */
-		cond_resched();
-		if (fatal_signal_pending(current)) {
-			await_bio_chain(bio);
-			return -EINTR;
-		}
+	while (!fatal_signal_pending(current)) {
+		bio = blk_alloc_discard_bio(bdev, &sector, &nr_sects, gfp_mask);
+		if (!bio)
+			return 0;
+		*biop = bio_chain_and_submit(*biop, bio);
 	}
 
-	*biop = bio;
-	return 0;
+	if (*biop)
+		await_bio_chain(*biop);
+	return -EINTR;
 }
 EXPORT_SYMBOL(__blkdev_issue_discard);
 
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 643d61b7cb82f7..74138c815657fd 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -826,4 +826,7 @@ struct bio *blk_next_bio(struct bio *bio, struct block_device *bdev,
 		unsigned int nr_pages, blk_opf_t opf, gfp_t gfp);
 struct bio *bio_chain_and_submit(struct bio *prev, struct bio *new);
 
+struct bio *blk_alloc_discard_bio(struct block_device *bdev,
+		sector_t *sector, sector_t *nr_sects, gfp_t gfp_mask);
+
 #endif /* __LINUX_BIO_H */
-- 
2.39.2