Re: [Qemu-devel] [PATCH 2/2] block-stream: include base into job node list

[Alberto Garcia]

On Thu 21 Feb 2019 04:26:39 PM CET, Andrey Shinkevich wrote:
> The block-stream job needs to own the base node as the limiter
> of the copy-on-read operation. So, the base node is included in
> the job node list (block_job_add_bdrv).
> Also, the block-stream job would not allow the base node to go
> away due to the graph modification, e.g. when a filter node is
> inserted between the bottom node and the base node.
> For that reason, the flag BLK_PERM_GRAPH_MOD is unset in the
> shared permission bit mask of the base node.
>
> Signed-off-by: Andrey Shinkevich <address@hidden>
> ---
>  block/stream.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/block/stream.c b/block/stream.c
> index 7a49ac0..c8f93d4 100644
> --- a/block/stream.c
> +++ b/block/stream.c
> @@ -259,6 +259,15 @@ void stream_start(const char *job_id, BlockDriverState 
> *bs,
>                             &error_abort);
>      }
>  
> +    if (base) {
> +        /*
> +         * The base node should not disappear during the job.
> +         */
> +        block_job_add_bdrv(&s->common, "base", base, 0,
> +                           BLK_PERM_ALL & ~BLK_PERM_GRAPH_MOD,
> +                           &error_abort);

I'm not sure if I understand the ~BLK_PERM_GRAPH_MOD bit, what's the
consequence of not removing that permission?

Berto