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Re: [Qemu-devel] [PATCH] block/mirror: limit qiov to IOV_MAX elements
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH] block/mirror: limit qiov to IOV_MAX elements |
Date: |
Wed, 1 Jul 2015 16:47:02 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.0.1 |
On 01/07/2015 16:45, 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 <address@hidden>
> Signed-off-by: Stefan Hajnoczi <address@hidden>
> ---
> 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) {
No Yoda conditions... apart from that,
Reviewed-by: Paolo Bonzini <address@hidden>
> + 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"
>