Commit cae98cb8 authored by Stefan Hajnoczi's avatar Stefan Hajnoczi Committed by Jeff Cody

block/mirror: limit qiov to IOV_MAX elements

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',

While the guest is running dd if=/dev/zero of=/var/tmp/foo oflag=direct

Cc: Jeff Cody <>
Signed-off-by: default avatarStefan Hajnoczi <>
Reviewed-by: default avatarPaolo Bonzini <>
Signed-off-by: default avatarJeff Cody <>
parent 2d697366
......@@ -245,6 +245,10 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
trace_mirror_break_buf_busy(s, nb_chunks, s->in_flight);
if (IOV_MAX < nb_chunks + added_chunks) {
trace_mirror_break_iov_max(s, nb_chunks, added_chunks);
/* We have enough free space to copy these sectors. */
bitmap_set(s->in_flight_bitmap, next_chunk, added_chunks);
......@@ -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"
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