Re: [Qemu-devel] [Qemu-block] [PATCH v2 02/16] block-backend: Add blk_request_perm

[Stefan Hajnoczi]

On Wed, Apr 19, 2017 at 05:43:42PM +0800, Fam Zheng wrote:
> This function tries to request, if not granted yet, for the given
> permissions.
> 
> Signed-off-by: Fam Zheng <address@hidden>
> ---
>  block/block-backend.c          | 12 ++++++++++++
>  include/sysemu/block-backend.h |  1 +
>  2 files changed, 13 insertions(+)
> 
> diff --git a/block/block-backend.c b/block/block-backend.c
> index 7405024..6bdd9ce 100644
> --- a/block/block-backend.c
> +++ b/block/block-backend.c
> @@ -629,6 +629,18 @@ void blk_resume_after_migration(Error **errp)
>      }
>  }
>  
> +int blk_request_perm(BlockBackend *blk, uint64_t perm, Error **errp)
> +{
> +    uint64_t blk_perm, shared_perm;
> +
> +    blk_get_perm(blk, &blk_perm, &shared_perm);
> +    if ((blk_perm & perm) == perm) {
> +        return 0;
> +    }
> +    blk_perm |= perm;
> +    return blk_set_perm(blk, blk_perm, shared_perm, errp);
> +}

I'm slightly confused about why this function is needed.  blk_set_perm()
doesn't do quite the right thing?

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