From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:60851) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZQFUe-0005DF-Uy for qemu-devel@nongnu.org; Fri, 14 Aug 2015 09:58:03 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZQFUZ-0002dP-T2 for qemu-devel@nongnu.org; Fri, 14 Aug 2015 09:58:00 -0400 From: Jeff Cody Date: Fri, 14 Aug 2015 09:57:46 -0400 Message-Id: <1439560667-28322-2-git-send-email-jcody@redhat.com> In-Reply-To: <1439560667-28322-1-git-send-email-jcody@redhat.com> References: <1439560667-28322-1-git-send-email-jcody@redhat.com> Subject: [Qemu-devel] [PULL 1/2] block/mirror: limit qiov to IOV_MAX elements List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-block@nongnu.org Cc: peter.maydell@linaro.org, jcody@redhat.com, qemu-devel@nongnu.org From: Stefan Hajnoczi 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 Reviewed-by: Paolo Bonzini Message-id: 1435761950-26714-1-git-send-email-stefanha@redhat.com Signed-off-by: Jeff Cody --- block/mirror.c | 4 ++++ trace-events | 1 + 2 files changed, 5 insertions(+) diff --git a/block/mirror.c b/block/mirror.c index fc4d8f5..0841964 100644 --- a/block/mirror.c +++ b/block/mirror.c @@ -245,6 +245,10 @@ 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 94bf3bb..8f9614a 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" -- 1.9.3