Re: [Qemu-block] [Qemu-devel] [PATCH] block: early check for blockers on drive-mirror

[John Snow]

On 02/07/2018 11:29 AM, Paolo Bonzini wrote:
> Even if an op blocker is present for BLOCK_OP_TYPE_MIRROR_SOURCE,
> it is checked a bit late and the result is that the target is
> created even if drive-mirror subsequently fails.  Add an early
> check to avoid this.
> 
> Signed-off-by: Paolo Bonzini <address@hidden>
> ---
>  blockdev.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/blockdev.c b/blockdev.c
> index 8e977eef11..c7e2e0a00e 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -3565,6 +3565,11 @@ void qmp_drive_mirror(DriveMirror *arg, Error **errp)
>          return;
>      }
>  
> +    /* Early check to avoid creating target */
> +    if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_MIRROR_SOURCE, errp)) {
> +        return;
> +    }
> +
>      aio_context = bdrv_get_aio_context(bs);
>      aio_context_acquire(aio_context);
>  
> 

What's the implication of the temporarily-extant target node that it
needs to be avoided so strictly?