[dm-devel] Re: dm: Fix alignment stacking on partitioned devices
Mike Snitzer
snitzer at redhat.com
Fri Dec 18 17:33:23 UTC 2009
On Fri, Dec 18 2009 at 2:30am -0500,
Martin K. Petersen <martin.petersen at oracle.com> wrote:
>
> The dm device limits function passes the start sector within the block
> device to the block layer stacking function. However, the partition's
> offset on the physical device is not added, resulting in incorrect
> alignment reporting.
>
> Add the partition offset to the values passed to blk_stack_limits().
>
> Signed-off-by: Martin K. Petersen <martin.petersen at oracle.com>
Martin,
This is not required because DM assumes alignment_offset has already
been accounted for by the caller (e.g. LVM2 or some other ficitional DM
consumer).
Below, "start" represents the aligned start of the data for a given volume.
That start must have already been shifted by alignment_offset; as is the
case with lvm2 (>= 2.02.51), see the following lvm2 commits:
http://sources.redhat.com/git/gitweb.cgi?p=lvm2.git;a=commit;h=282029eb45e56
http://sources.redhat.com/git/gitweb.cgi?p=lvm2.git;a=commit;h=6c88b6c660020
All this being said, how did you arrive at this patch? Why do you feel
it is needed? Was it just from code inspection?
Regards,
Mike
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index be62547..67efac9 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -495,6 +495,7 @@ int dm_set_device_limits(struct dm_target *ti, struct dm_dev *dev,
> struct queue_limits *limits = data;
> struct block_device *bdev = dev->bdev;
> struct request_queue *q = bdev_get_queue(bdev);
> + sector_t offset = (get_start_sect(bdev) + start) << 9;
> char b[BDEVNAME_SIZE];
>
> if (unlikely(!q)) {
> @@ -503,7 +504,7 @@ int dm_set_device_limits(struct dm_target *ti, struct dm_dev *dev,
> return 0;
> }
>
> - if (blk_stack_limits(limits, &q->limits, start << 9) < 0)
> + if (blk_stack_limits(limits, &q->limits, offset) < 0)
> DMWARN("%s: target device %s is misaligned: "
> "physical_block_size=%u, logical_block_size=%u, "
> "alignment_offset=%u, start=%llu",
> @@ -511,7 +512,7 @@ int dm_set_device_limits(struct dm_target *ti, struct dm_dev *dev,
> q->limits.physical_block_size,
> q->limits.logical_block_size,
> q->limits.alignment_offset,
> - (unsigned long long) start << 9);
> + (unsigned long long) offset);
>
>
> /*
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