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From: Stefan Hajnoczi <stefanha@redhat.com>
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Date: Wed, 1 Jul 2015 15:45:50 +0100
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Subject: [PATCH] block/mirror: limit qiov to IOV_MAX elements
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If mirror has more free buffers than IOV_MAX, preadv(2)/pwritev(2)
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EINVAL failures may be encountered.
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It is possible to trigger this by setting granularity to a low value
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like 8192.
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This patch stops appending chunks once IOV_MAX is reached.
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The spurious EINVAL failure can be reproduced with a qcow2 image file
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and the following QMP invocation:
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qmp.command('drive-mirror', device='virtio0', target='/tmp/r7.s1',
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granularity=8192, sync='full', mode='absolute-paths',
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format='raw')
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While the guest is running dd if=/dev/zero of=/var/tmp/foo oflag=direct
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bs=4k.
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Cc: Jeff Cody <jcody@redhat.com>
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
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Message-id: 1435761950-26714-1-git-send-email-stefanha@redhat.com
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Signed-off-by: Jeff Cody <jcody@redhat.com>
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(cherry picked from commit cae98cb87d269c33d23b2bccd79bb8d99a60d811)
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---
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block/mirror.c | 4 ++++
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trace-events | 1 +
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2 files changed, 5 insertions(+)
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diff --git a/block/mirror.c b/block/mirror.c
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index bd079a4..9407287 100644
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--- a/block/mirror.c
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+++ b/block/mirror.c
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@@ -248,6 +248,10 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
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trace_mirror_break_buf_busy(s, nb_chunks, s->in_flight);
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break;
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}
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+ if (IOV_MAX < nb_chunks + added_chunks) {
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+ trace_mirror_break_iov_max(s, nb_chunks, added_chunks);
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+ break;
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+ }
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/* We have enough free space to copy these sectors. */
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bitmap_set(s->in_flight_bitmap, next_chunk, added_chunks);
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diff --git a/trace-events b/trace-events
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index 30eba92..6f992c4 100644
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--- a/trace-events
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+++ b/trace-events
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@@ -94,6 +94,7 @@ mirror_yield(void *s, int64_t cnt, int buf_free_count, int in_flight) "s %p dirt
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mirror_yield_in_flight(void *s, int64_t sector_num, int in_flight) "s %p sector_num %"PRId64" in_flight %d"
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mirror_yield_buf_busy(void *s, int nb_chunks, int in_flight) "s %p requested chunks %d in_flight %d"
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mirror_break_buf_busy(void *s, int nb_chunks, int in_flight) "s %p requested chunks %d in_flight %d"
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+mirror_break_iov_max(void *s, int nb_chunks, int added_chunks) "s %p requested chunks %d added_chunks %d"
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# block/backup.c
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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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