Re: [PATCH 3/3] block: Introduce blkdev_issue_zeroout_discard() function

[Christoph Hellwig <hch@infradead.org>]

On Fri, Nov 07, 2014 at 12:08:14AM -0500, Martin K. Petersen wrote:
> blkdev_issue_discard() will zero a given block range on disk. This is
> done by way of either WRITE SAME or regular WRITE. I.e. the blocks on
> disk will be written and thus provisioned.
> 
> There are use cases where the desired behavior is to zero the blocks but
> unprovision them if possible. The blocks must deterministically contain
> zeroes when they are subsequently read back.
> 
> This patch introduces a blkdev_issue_zeroout_discard() call that
> provides this functionality. If a block device guarantees
> discard_zeroes_data the new function will use discard to clear the block
> range. If the device does not support discard_zeroes_data or if the
> discard request fails we will fall back to blkdev_issue_zeroout() to
> ensure predictable results.

I'm not a fan of adding another function here and would prefer a flag,
but it looks correct, so:

Reviewed-by: Christoph Hellwig <hch@lst.de>