tree 3fcb794cbd50958839c955ec492b3fb25fd801b6
parent 979570e02981d4a8fc20b3cc8fd651856c98ee9d
author Mike Snitzer <snitzer@redhat.com> 1348699539 +0100
committer Alasdair G Kergon <agk@redhat.com> 1348699539 +0100

dm thin: do not set discard_zeroes_data

The dm thin pool target claims to support the zeroing of discarded
data areas.  This turns out to be incorrect when processing discards
that do not exactly cover a complete number of blocks, so the target
must always set discard_zeroes_data_unsupported.

The thin pool target will zero blocks when they are allocated if the
skip_block_zeroing feature is not specified.  The block layer
may send a discard that only partly covers a block.  If a thin pool
block is partially discarded then there is no guarantee that the
discarded data will get zeroed before it is accessed again.
Due to this, thin devices cannot claim discards will always zero data.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Joe Thornber <ejt@redhat.com>
Cc: stable@vger.kernel.org # 3.4+
Signed-off-by: Alasdair G Kergon <agk@redhat.com>