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-   -   block: Implement support for WRITE SAME (http://www.linux-archive.org/device-mapper-development/630554-block-implement-support-write-same.html)

Mike Snitzer 02-09-2012 02:33 AM

block: Implement support for WRITE SAME
 
On Wed, Feb 08 2012 at 6:12pm -0500,
Martin K. Petersen <martin.petersen@oracle.com> wrote:

> >>>>> "Mike" == Mike Snitzer <snitzer@redhat.com> writes:
>
> >> + BUG_ON(length != bdev_logical_block_size(bdev));
>
> Mike> Why require @length to be passed in if we can easily determine the
> Mike> only correct length, via bdev_logical_block_size, locally?
>
> Just sanity checking since the caller is passing in a buffer pointer.
> See my comment in the patch series introduction about a page vs a
> buffer. I don't really care whether we pick one or the other. Whatever
> makes the most sense to dm, md and the filesystems...

OK, I see -- might make sense to use a page. But I don't have a
strong opinion (and not sure I will have one in the near-term).

I wrote a patch for dm-kcopyd (and dm-io) to add support for WRITE_SAME,
but it doesn't use the new blkdev_* interfaces you've provided -- only
because I needed to wire it up to dm-thinp which uses dm_kcopyd_zero()
to provide async zeroing.

So the patch open codes a small portion of bio prep code from
blkdev_issue_write_same() in dm-io's do_region(). I'll post it once I
verify it works.

Mike

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