Re: [Qemu-devel] [RFC PATCH 1/3] block: add target-id option to drive-backup QMP command

[Stefan Hajnoczi <stefanha@redhat.com>]

On Wed, Jun 26, 2013 at 11:59:19AM +0800, Fam Zheng wrote:
> Add target-id (optional) to drive-backup command, to make the target bs
> a named drive so that we can operate on it (e.g. export with NBD).
> 
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  blockdev.c       | 4 +++-
>  qapi-schema.json | 7 +++++--
>  qmp-commands.hx  | 3 ++-
>  3 files changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/blockdev.c b/blockdev.c
> index b3a57e0..5e694f3 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -935,6 +935,7 @@ static void drive_backup_prepare(BlkTransactionState *common, Error **errp)
>      backup = common->action->drive_backup;
>  
>      qmp_drive_backup(backup->device, backup->target,
> +                     backup->has_target_id, backup->target_id,
>                       backup->has_format, backup->format,
>                       backup->has_mode, backup->mode,
>                       backup->has_speed, backup->speed,
> @@ -1420,6 +1421,7 @@ void qmp_block_commit(const char *device,
>  }
>  
>  void qmp_drive_backup(const char *device, const char *target,
> +                      bool has_target_id, const char *target_id,
>                        bool has_format, const char *format,
>                        bool has_mode, enum NewImageMode mode,
>                        bool has_speed, int64_t speed,
> @@ -1494,7 +1496,7 @@ void qmp_drive_backup(const char *device, const char *target,
>          return;
>      }
>  
> -    target_bs = bdrv_new("");
> +    target_bs = bdrv_new(has_target_id ? target_id : "");

This raises a new issue:

Now that the target can be named, what happens when the user issues a
monitor command, e.g. drive-del, block-resize, or drive-backup :)?

We have a clumsy form of protection with bdrv_set_in_use().  It makes
several monitor commands refuse with -EBUSY.

Perhaps we should have a command permission set so it's possible to
allow/deny specific commands.

Stefan