Re: [Qemu-devel] [PATCH 3/4] mirror: Keep target drained until graph changes are done

[Eric Blake]

On 7/25/19 11:27 AM, Kevin Wolf wrote:
> Calling bdrv_drained_end() for target_bs can restarts requests too

restart

> early, so that they would execute on mirror_top_bs, which however has
> already dropped all permissions.
> 
> Keep the target node drained until all graph changes have completed.
> 
> Signed-off-by: Kevin Wolf <address@hidden>
> ---
>  block/mirror.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/block/mirror.c b/block/mirror.c
> index 8cb75fb409..7483051f8d 100644
> --- a/block/mirror.c
> +++ b/block/mirror.c
> @@ -644,6 +644,11 @@ static int mirror_exit_common(Job *job)
>      bdrv_ref(mirror_top_bs);
>      bdrv_ref(target_bs);
>  
> +    /* The mirror job has no requests in flight any more, but we need to
> +     * drain potential other users of the BDS before changing the graph. */

Is checkpatch going to gripe about your comment style,

> +    assert(s->in_drain);
> +    bdrv_drained_begin(target_bs);
> +
>      /* Remove target parent that still uses BLK_PERM_WRITE/RESIZE before
>       * inserting target_bs at s->to_replace, where we might not be able to 
> get
>       * these permissions.
> @@ -684,12 +689,7 @@ static int mirror_exit_common(Job *job)
>              bdrv_reopen_set_read_only(target_bs, ro, NULL);
>          }
>  
> -        /* The mirror job has no requests in flight any more, but we need to
> -         * drain potential other users of the BDS before changing the graph. 
> */

even though it is just code motion?

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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