From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37935) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZMeqY-0006dN-Da for qemu-devel@nongnu.org; Tue, 04 Aug 2015 12:13:47 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZMeqS-0004k7-46 for qemu-devel@nongnu.org; Tue, 04 Aug 2015 12:13:46 -0400 MIME-Version: 1.0 In-Reply-To: <1435761950-26714-1-git-send-email-stefanha@redhat.com> References: <1435761950-26714-1-git-send-email-stefanha@redhat.com> Date: Tue, 4 Aug 2015 17:13:39 +0100 Message-ID: From: Stefan Hajnoczi Content-Type: text/plain; charset=UTF-8 Subject: Re: [Qemu-devel] [Qemu-block] [PATCH] block/mirror: limit qiov to IOV_MAX elements List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: Paolo Bonzini , Jeff Cody , qemu-devel , qemu block Sorry Jeff, my "Cc:" line in the commit description wasn't picked up. Please merge through your block/jobs tree for QEMU 2.5. Thanks, Stefan On Wed, Jul 1, 2015 at 3:45 PM, Stefan Hajnoczi wrote: > If mirror has more free buffers than IOV_MAX, preadv(2)/pwritev(2) > EINVAL failures may be encountered. > > It is possible to trigger this by setting granularity to a low value > like 8192. > > This patch stops appending chunks once IOV_MAX is reached. > > The spurious EINVAL failure can be reproduced with a qcow2 image file > and the following QMP invocation: > > qmp.command('drive-mirror', device='virtio0', target='/tmp/r7.s1', > granularity=8192, sync='full', mode='absolute-paths', > format='raw') > > While the guest is running dd if=/dev/zero of=/var/tmp/foo oflag=direct > bs=4k. > > Cc: Jeff Cody > Signed-off-by: Stefan Hajnoczi > --- > block/mirror.c | 4 ++++ > trace-events | 1 + > 2 files changed, 5 insertions(+) > > diff --git a/block/mirror.c b/block/mirror.c > index 048e452..985ad00 100644 > --- a/block/mirror.c > +++ b/block/mirror.c > @@ -241,6 +241,10 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s) > trace_mirror_break_buf_busy(s, nb_chunks, s->in_flight); > break; > } > + if (IOV_MAX < nb_chunks + added_chunks) { > + trace_mirror_break_iov_max(s, nb_chunks, added_chunks); > + break; > + } > > /* We have enough free space to copy these sectors. */ > bitmap_set(s->in_flight_bitmap, next_chunk, added_chunks); > diff --git a/trace-events b/trace-events > index 52b7efa..943cd0c 100644 > --- a/trace-events > +++ b/trace-events > @@ -94,6 +94,7 @@ mirror_yield(void *s, int64_t cnt, int buf_free_count, int in_flight) "s %p dirt > mirror_yield_in_flight(void *s, int64_t sector_num, int in_flight) "s %p sector_num %"PRId64" in_flight %d" > mirror_yield_buf_busy(void *s, int nb_chunks, int in_flight) "s %p requested chunks %d in_flight %d" > mirror_break_buf_busy(void *s, int nb_chunks, int in_flight) "s %p requested chunks %d in_flight %d" > +mirror_break_iov_max(void *s, int nb_chunks, int added_chunks) "s %p requested chunks %d added_chunks %d" > > # block/backup.c > backup_do_cow_enter(void *job, int64_t start, int64_t sector_num, int nb_sectors) "job %p start %"PRId64" sector_num %"PRId64" nb_sectors %d" > -- > 2.4.3 > >