From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:52344) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b5WXP-00019u-CB for qemu-devel@nongnu.org; Wed, 25 May 2016 06:59:46 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1b5WXE-0002WU-RO for qemu-devel@nongnu.org; Wed, 25 May 2016 06:59:40 -0400 Received: from resqmta-po-05v.sys.comcast.net ([2001:558:fe16:19:96:114:154:164]:59989) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b5WXD-0002VO-Gh for qemu-devel@nongnu.org; Wed, 25 May 2016 06:59:32 -0400 From: Eric Blake Date: Wed, 25 May 2016 04:59:25 -0600 Message-Id: <1464173965-9694-1-git-send-email-eblake@redhat.com> Subject: [Qemu-devel] [PATCH v2] nbd: Don't trim unrequested bytes List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: kwolf@redhat.com, pbonzini@redhat.com, qemu-block@nongnu.org, qemu-stable@nongnu.org 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 --- v2: don't underflow request.len on sub-sector requests nbd/server.c | 20 ++++++++++++++------ 1 file changed, 14 insertions(+), 6 deletions(-) diff --git a/nbd/server.c b/nbd/server.c index fa862cd..b2cfeb9 100644 --- a/nbd/server.c +++ b/nbd/server.c @@ -1153,12 +1153,20 @@ 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, - request.len / BDRV_SECTOR_SIZE); - if (ret < 0) { - LOG("discard failed"); - reply.error = -ret; + /* 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; -- 2.5.5