[Drbd-dev] [PATCH 25/27] block: remove the discard_zeroes_data flag

[hch at lst.de]

On Tue, May 02, 2017 at 08:33:15PM -0700, Nicholas A. Bellinger wrote:
> The larger target/iblock conversion patch looks like post v4.12 material
> at this point, so to avoid breakage wrt to existing LBPRZ behavior, I'll
> plan to push the following patch post -rc1.

I don't think this is safe.  If you want to do the aboe you also
need to ensure ->execute_unmap always zeroes the data.  For actual
files in the file backend we should be all fine, but for the block
device case [1] and iblock we'd need to use blkdev_issue_zeroout
instead of blkdev_issue_discard when unmap_zeroes_data is set.

[1] which btw already seems broken as it doesn't invalidate cached
data when issuing a discard.