block: introduce BLKDEV_DISCARD_ZERO to fix zeroout

Currently blkdev_issue_zeroout cascades down from discards (if the driver
guarantees that discards zero data), to WRITE SAME and then to a loop
writing zeroes.  Unfortunately we ignore run-time EOPNOTSUPP errors in the
block layer blkdev_issue_discard helper to work around DM volumes that
may have mixed discard support underneath.

This patch intoroduces a new BLKDEV_DISCARD_ZERO flag to
blkdev_issue_discard that indicates we are called for zeroing operation.
This allows both to ignore the EOPNOTSUPP hack and actually consolidating
the discard_zeroes_data check into the function.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 11 insertions, 6 deletions

diff --git a/block/blk-lib.c b/block/blk-lib.c
index 78626c2fde33..45b35b15496f 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -36,12 +36,17 @@ int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
                 return -ENXIO;
 
         if (flags & BLKDEV_DISCARD_SECURE) {
+                if (flags & BLKDEV_DISCARD_ZERO)
+                        return -EOPNOTSUPP;
                 if (!blk_queue_secure_erase(q))
                         return -EOPNOTSUPP;
                 op = REQ_OP_SECURE_ERASE;
         } else {
                 if (!blk_queue_discard(q))
                         return -EOPNOTSUPP;
+                if ((flags & BLKDEV_DISCARD_ZERO) &&
+                    !q->limits.discard_zeroes_data)
+                        return -EOPNOTSUPP;
                 op = REQ_OP_DISCARD;
         }
 
@@ -116,7 +121,7 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
                         &bio);
         if (!ret && bio) {
                 ret = submit_bio_wait(bio);
-                if (ret == -EOPNOTSUPP)
+                if (ret == -EOPNOTSUPP && !(flags & BLKDEV_DISCARD_ZERO))
                         ret = 0;
         }
         blk_finish_plug(&plug);
@@ -241,11 +246,11 @@ static int __blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
 int blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
                          sector_t nr_sects, gfp_t gfp_mask, bool discard)
 {
-        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)
-                return 0;
+        if (discard) {
+                if (!blkdev_issue_discard(bdev, sector, nr_sects, gfp_mask,
+                                BLKDEV_DISCARD_ZERO))
+                        return 0;
+        }
 
         if (bdev_write_same(bdev) &&
             blkdev_issue_write_same(bdev, sector, nr_sects, gfp_mask,