From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39356) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b5UDs-0006bq-BG for qemu-devel@nongnu.org; Wed, 25 May 2016 04:31:25 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1b5UDp-0007kY-4c for qemu-devel@nongnu.org; Wed, 25 May 2016 04:31:24 -0400 Sender: Paolo Bonzini References: <1464151079-4341-1-git-send-email-eblake@redhat.com> From: Paolo Bonzini Message-ID: <18efe9a1-d22c-fa23-66c5-64cc7db0ff02@redhat.com> Date: Wed, 25 May 2016 10:31:10 +0200 MIME-Version: 1.0 In-Reply-To: <1464151079-4341-1-git-send-email-eblake@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] nbd: Don't trim unrequested bytes List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eric Blake , qemu-devel@nongnu.org Cc: kwolf@redhat.com, qemu-stable@nongnu.org, qemu-block@nongnu.org On 25/05/2016 06:37, Eric Blake wrote: > 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 > --- > nbd/server.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/nbd/server.c b/nbd/server.c > index fa862cd..5aed8db 100644 > --- a/nbd/server.c > +++ b/nbd/server.c > @@ -1153,8 +1153,12 @@ 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 */ > + 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"); > Thanks, queued for 2.7. Paolo