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[PATCH v2 2/3] block: reorganize rounding of max_discard_sectors

To: linux-kernel@xxxxxxxxxxxxxxx
Subject: [PATCH v2 2/3] block: reorganize rounding of max_discard_sectors
From: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Date: Mon, 2 Jul 2012 15:20:24 +0200
Cc: snitzer@xxxxxxxxxx, david@xxxxxxxxxxxxx, dm-devel@xxxxxxxxxx, xfs@xxxxxxxxxxx, hch@xxxxxx, martin.petersen@xxxxxxxxxx, axboe@xxxxxxxxx
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Sender: Paolo Bonzini <paolo.bonzini@xxxxxxxxx>
Mostly a preparation for the next patch.

In principle this fixes an infinite loop if max_discard_sectors < granularity,
but that really shouldn't happen.

Cc: Jens Axboe <axboe@xxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 block/blk-lib.c |    9 +++++----
 1 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/block/blk-lib.c b/block/blk-lib.c
index 2b461b4..16b06f6 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -44,6 +44,7 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t 
sector,
        struct request_queue *q = bdev_get_queue(bdev);
        int type = REQ_WRITE | REQ_DISCARD;
        unsigned int max_discard_sectors;
+       unsigned int granularity;
        struct bio_batch bb;
        struct bio *bio;
        int ret = 0;
@@ -54,18 +55,18 @@ int blkdev_issue_discard(struct block_device *bdev, 
sector_t sector,
        if (!blk_queue_discard(q))
                return -EOPNOTSUPP;
 
+       /* Zero-sector (unknown) and one-sector granularities are the same.  */
+       granularity = max(q->limits.discard_granularity >> 9, 1U);
+
        /*
         * Ensure that max_discard_sectors is of the proper
         * granularity
         */
        max_discard_sectors = min(q->limits.max_discard_sectors, UINT_MAX >> 9);
+       max_discard_sectors = round_down(max_discard_sectors, granularity);
        if (unlikely(!max_discard_sectors)) {
                /* Avoid infinite loop below. Being cautious never hurts. */
                return -EOPNOTSUPP;
-       } else if (q->limits.discard_granularity) {
-               unsigned int disc_sects = q->limits.discard_granularity >> 9;
-
-               max_discard_sectors &= ~(disc_sects - 1);
        }
 
        if (flags & BLKDEV_DISCARD_SECURE) {
-- 
1.7.1


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