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nbd: Don't trim unrequested bytes

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Similar to commit df7b97ff, we are mishandling clients that
give an unaligned NBD_CMD_TRIM request, and potentially
trimming bytes that occur before their request; which in turn
can cause potential unintended data loss (unlikely in
practice, since most clients are sane and issue aligned trim
requests).  However, while we fixed read and write by switching
to the byte interfaces of blk_, we don't yet have a byte
interface for discard.  On the other hand, trim is advisory, so
rounding the user's request to simply ignore the first and last
unaligned sectors (or the entire request, if it is sub-sector
in length) is just fine.

CC: qemu-stable@nongnu.org
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1464173965-9694-1-git-send-email-eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 353ab96973)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
This commit is contained in:
Eric Blake 2016-05-25 04:59:25 -06:00 committed by Michael Roth
parent 509e13298f
commit fb26337641
1 changed files with 14 additions and 6 deletions
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12
nbd/server.c
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@ -1153,13 +1153,21 @@ static void nbd_trip(void *opaque)
break;
case NBD_CMD_TRIM:
TRACE("Request type is TRIM");
ret = blk_co_discard(exp->blk, (request.from + exp->dev_offset)
/ BDRV_SECTOR_SIZE,
/* Ignore unaligned head or tail, until block layer adds byte
* interface */
if (request.len >= BDRV_SECTOR_SIZE) {
request.len -= (request.from + request.len) % BDRV_SECTOR_SIZE;
ret = blk_co_discard(exp->blk,
DIV_ROUND_UP(request.from + exp->dev_offset,
BDRV_SECTOR_SIZE),
request.len / BDRV_SECTOR_SIZE);
if (ret < 0) {
LOG("discard failed");
reply.error = -ret;
}
} else {
TRACE("trim request too small, ignoring");
}
if (nbd_co_send_reply(req, &reply, 0) < 0) {
goto out;
}