Re: [Qemu-devel] [PATCH 1/3] block: Allow x-blockdev-del on a BB with a monitor-owned BDS

[Eric Blake <eblake@redhat.com>]

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On 02/08/2016 07:14 AM, Alberto Garcia wrote:

When sending a multi-patch series, you should always include a 0/3 cover
letter.  The cover letter is optional only for a lone patch.

> When x-blockdev-del is performed on a BlockBackend that has inserted
> media it will only succeed if the BDS doesn't have any additional
> references.
> 
> The only problem with this is that if the BDS was created separately
> using blockdev-add then the backend won't be able to be destroyed
> unless the BDS is ejected first. This is an unnecessary restriction.
> 
> Now that we have a list of monitor-owned BDSs we can allow
> x-blockdev-del to work in this scenario if the BDS has exactly one
> extra reference and that reference is from the monitor.
> 
> Signed-off-by: Alberto Garcia <berto@igalia.com>
> ---
>  blockdev.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/blockdev.c b/blockdev.c
> index e1b6b0f..847058d 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -3966,9 +3966,16 @@ void qmp_x_blockdev_del(bool has_id, const char *id,
>          }
>  
>          if (bs->refcnt > 1) {
> -            error_setg(errp, "Block device %s is in use",
> -                       bdrv_get_device_or_node_name(bs));
> -            goto out;
> +            /* We allow deleting a BlockBackend that has a BDS with an
> +             * extra reference if that extra reference is from the
> +             * monitor. */
> +            bool bs_has_only_monitor_ref =
> +                blk && bs->monitor_list.tqe_prev && bs->refcnt == 2;
> +            if (!bs_has_only_monitor_ref) {

I don't think the temporary bool or nested 'if' are necessary; but at
the same time, I don't think the following is any more legible:

/* Prohibit deleting a BlockBackend whose BDS is in use by any more than
a single monitor */
if (bs->refcnt > 1 + (blk && bs->monitor_list.tqe_prev)) {
    error_setg(...

so I could live with your patch as-is:
Reviewed-by: Eric Blake <eblake@redhat.com>


-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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