From: Eric Blake Date: Wed, 25 May 2016 10:59:25 +0000 (-0600) Subject: nbd: Don't trim unrequested bytes X-Git-Url: http://git.osdn.net/view?a=commitdiff_plain;h=353ab969730742b7392414d62f4ba9632e8cf22c;p=qmiga%2Fqemu.git nbd: Don't trim unrequested bytes 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 Message-Id: <1464173965-9694-1-git-send-email-eblake@redhat.com> Signed-off-by: Paolo Bonzini --- diff --git a/nbd/server.c b/nbd/server.c index fa862cd622..b2cfeb9843 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;