Re: [Qemu-devel] [PATCH v4 7/7] block: Allow backup on referenced named BlockDriverState

[Kevin Wolf]

Am 22.11.2013 um 06:24 hat Fam Zheng geschrieben:
> Drive backup is a read only operation on source bs. We want to allow
> this specific case to enable image-fleecing. Note that when
> image-fleecing job starts, the job still add its blocker to source bs,
> and any other operation on it will be blocked by that.
> 
> Signed-off-by: Fam Zheng <address@hidden>
> ---
>  block.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/block.c b/block.c
> index a5da656..d30be51 100644
> --- a/block.c
> +++ b/block.c
> @@ -1179,6 +1179,8 @@ int bdrv_open(BlockDriverState *bs, const char 
> *filename, QDict *options,
>                             "device is used as backing hd of '%s'",
>                             bs->device_name);
>                  bdrv_op_block_all(bs->backing_hd, bs->backing_blocker);
> +                bdrv_op_unblock(bs->backing_hd, BLOCK_OP_TYPE_BACKUP,
> +                                bs->backing_blocker);
>                  pstrcpy(bs->backing_file, sizeof(bs->backing_file),
>                          bs->backing_hd->filename);
>                  pstrcpy(bs->backing_format, sizeof(bs->backing_format),

We probably need separate blockers for "can be a backup source" and "can
be a backup target". Because I think this allows using it as a
read-write target as well, which was not intended.

Do we need to cover this in other parts of the code as well, like when
adding a new BDS during external snapshot creation?

Kevin