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    Subject[PATCH 5.4 118/411] virtio_blk: fix the discard_granularity and discard_alignment queue limits
    Date
    From: Christoph Hellwig <hch@lst.de>

    [ Upstream commit 62952cc5bccd89b76d710de1d0b43244af0f2903 ]

    The discard_alignment queue limit is named a bit misleading means the
    offset into the block device at which the discard granularity starts.

    On the other hand the discard_sector_alignment from the virtio 1.1 looks
    similar to what Linux uses as discard granularity (even if not very well
    described):

    "discard_sector_alignment can be used by OS when splitting a request
    based on alignment. "

    And at least qemu does set it to the discard granularity.

    So stop setting the discard_alignment and use the virtio
    discard_sector_alignment to set the discard granularity.

    Fixes: 1f23816b8eb8 ("virtio_blk: add discard and write zeroes support")
    Signed-off-by: Christoph Hellwig <hch@lst.de>
    Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
    Link: https://lore.kernel.org/r/20220418045314.360785-5-hch@lst.de
    Signed-off-by: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/block/virtio_blk.c | 7 ++++---
    1 file changed, 4 insertions(+), 3 deletions(-)

    diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
    index 2a5cd502feae..9b3ea86c20e5 100644
    --- a/drivers/block/virtio_blk.c
    +++ b/drivers/block/virtio_blk.c
    @@ -976,11 +976,12 @@ static int virtblk_probe(struct virtio_device *vdev)
    blk_queue_io_opt(q, blk_size * opt_io_size);

    if (virtio_has_feature(vdev, VIRTIO_BLK_F_DISCARD)) {
    - q->limits.discard_granularity = blk_size;
    -
    virtio_cread(vdev, struct virtio_blk_config,
    discard_sector_alignment, &v);
    - q->limits.discard_alignment = v ? v << SECTOR_SHIFT : 0;
    + if (v)
    + q->limits.discard_granularity = v << SECTOR_SHIFT;
    + else
    + q->limits.discard_granularity = blk_size;

    virtio_cread(vdev, struct virtio_blk_config,
    max_discard_sectors, &v);
    --
    2.35.1


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