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[PATCH] block: correctly fallback for zeroout

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[PATCH] block: correctly fallback for zeroout

Shaohua Li-3
blkdev_issue_zeroout try discard/writesame first, if they fail, zeroout
fallback to regular write. The problem is discard/writesame doesn't
return error for -EOPNOTSUPP, then zeroout can't do fallback and leave
disk data not changed. zeroout should have guaranteed zero-fill
behavior.

BTW, I saw several callers of blkdev_issue_discard can handle
-EOPNOTSUPP, not sure why blkdev_issue_discard not returns -EOPNOTSUPP.
The same story for blkdev_issue_write_same.

https://bugzilla.kernel.org/show_bug.cgi?id=118581

Cc: Sitsofe Wheeler <[hidden email]>
Cc: Mike Snitzer <[hidden email]>
Cc: Jens Axboe <[hidden email]>
Cc: Martin K. Petersen <[hidden email]>
Signed-off-by: Shaohua Li <[hidden email]>
---
 block/blk-lib.c | 35 ++++++++++++++++++++++++++---------
 1 file changed, 26 insertions(+), 9 deletions(-)

diff --git a/block/blk-lib.c b/block/blk-lib.c
index 23d7f30..232f9ea 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -95,8 +95,9 @@ EXPORT_SYMBOL(__blkdev_issue_discard);
  * Description:
  *    Issue a discard request for the sectors in question.
  */
-int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
- sector_t nr_sects, gfp_t gfp_mask, unsigned long flags)
+static int do_blkdev_issue_discard(struct block_device *bdev, sector_t sector,
+ sector_t nr_sects, gfp_t gfp_mask, unsigned long flags,
+ bool ignore_nosupport)
 {
  int type = REQ_WRITE | REQ_DISCARD;
  struct bio *bio = NULL;
@@ -111,13 +112,20 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
  &bio);
  if (!ret && bio) {
  ret = submit_bio_wait(type, bio);
- if (ret == -EOPNOTSUPP)
+ if (ignore_nosupport && ret == -EOPNOTSUPP)
  ret = 0;
  }
  blk_finish_plug(&plug);
 
  return ret;
 }
+
+int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
+ sector_t nr_sects, gfp_t gfp_mask, unsigned long flags)
+{
+ return do_blkdev_issue_discard(bdev, sector, nr_sects, gfp_mask,
+ flags, true);
+}
 EXPORT_SYMBOL(blkdev_issue_discard);
 
 /**
@@ -131,9 +139,9 @@ EXPORT_SYMBOL(blkdev_issue_discard);
  * Description:
  *    Issue a write same request for the sectors in question.
  */
-int blkdev_issue_write_same(struct block_device *bdev, sector_t sector,
+static int do_blkdev_issue_write_same(struct block_device *bdev, sector_t sector,
     sector_t nr_sects, gfp_t gfp_mask,
-    struct page *page)
+    struct page *page, bool ignore_nosupport)
 {
  struct request_queue *q = bdev_get_queue(bdev);
  unsigned int max_write_same_sectors;
@@ -167,7 +175,15 @@ int blkdev_issue_write_same(struct block_device *bdev, sector_t sector,
 
  if (bio)
  ret = submit_bio_wait(REQ_WRITE | REQ_WRITE_SAME, bio);
- return ret != -EOPNOTSUPP ? ret : 0;
+ return (ret != -EOPNOTSUPP || !ignore_nosupport) ? ret : 0;
+}
+
+int blkdev_issue_write_same(struct block_device *bdev, sector_t sector,
+    sector_t nr_sects, gfp_t gfp_mask,
+    struct page *page)
+{
+ return do_blkdev_issue_write_same(bdev, sector, nr_sects, gfp_mask,
+ page, true);
 }
 EXPORT_SYMBOL(blkdev_issue_write_same);
 
@@ -238,12 +254,13 @@ int blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
  struct request_queue *q = bdev_get_queue(bdev);
 
  if (discard && blk_queue_discard(q) && q->limits.discard_zeroes_data &&
-    blkdev_issue_discard(bdev, sector, nr_sects, gfp_mask, 0) == 0)
+    do_blkdev_issue_discard(bdev, sector, nr_sects, gfp_mask, 0,
+ false) == 0)
  return 0;
 
  if (bdev_write_same(bdev) &&
-    blkdev_issue_write_same(bdev, sector, nr_sects, gfp_mask,
-    ZERO_PAGE(0)) == 0)
+    do_blkdev_issue_write_same(bdev, sector, nr_sects, gfp_mask,
+    ZERO_PAGE(0), false) == 0)
  return 0;
 
  return __blkdev_issue_zeroout(bdev, sector, nr_sects, gfp_mask);
--
2.8.0.rc2

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