Re: [Qemu-devel] [PATCH V7 02/14] block: add bdrv_can_read_snapshot() function

[Markus Armbruster]

Wenchao Xia <address@hidden> writes:

>   Compared to bdrv_can_snapshot(), this function return whether
> bs* is ready to read snapshot info from instead of write. If yes,
> caller can then query snapshot information, but taking snapshot
> is not always possible for that *bs may be read only.
>
> Signed-off-by: Wenchao Xia <address@hidden>
> Reviewed-by: Eric Blake <address@hidden>
> ---
>  block.c               |   19 +++++++++++++++++++
>  include/block/block.h |    1 +
>  2 files changed, 20 insertions(+), 0 deletions(-)
>
> diff --git a/block.c b/block.c
> index 50dab8e..19c2d7b 100644
> --- a/block.c
> +++ b/block.c
> @@ -3058,6 +3058,25 @@ bool bdrv_debug_is_suspended(BlockDriverState *bs, 
> const char *tag)
>  /**************************************************************/
>  /* handling of snapshots */
>  
> +/* return whether internal snapshot can be read on @bs */
> +bool bdrv_can_read_snapshot(BlockDriverState *bs)
> +{
> +    BlockDriver *drv = bs->drv;
> +    if (!drv || !bdrv_is_inserted(bs)) {
> +        return false;
> +    }
> +
> +    if (!drv->bdrv_snapshot_create) {
> +        if (bs->file != NULL) {
> +            return bdrv_can_read_snapshot(bs->file);
> +        }
> +        return false;
> +    }
> +
> +    return true;
> +}

Looks like

bdrv_can_read_snapshot(bs) && !bdrv_is_read_only(bs) == bdrv_can_snapshot(bs)

Correct?

> +
> +/* return whether internal snapshot can be write on @bs */

"be written".

Or more succinctly:

/* Can @bs take a snapshot?  */

>  int bdrv_can_snapshot(BlockDriverState *bs)
>  {
>      BlockDriver *drv = bs->drv;
> diff --git a/include/block/block.h b/include/block/block.h
> index 5c3b911..4c48052 100644
> --- a/include/block/block.h
> +++ b/include/block/block.h
> @@ -321,6 +321,7 @@ void bdrv_get_full_backing_filename(BlockDriverState *bs,
>                                      char *dest, size_t sz);
>  BlockInfo *bdrv_query_info(BlockDriverState *s);
>  BlockStats *bdrv_query_stats(const BlockDriverState *bs);
> +bool bdrv_can_read_snapshot(BlockDriverState *bs);
>  int bdrv_can_snapshot(BlockDriverState *bs);
>  int bdrv_is_snapshot(BlockDriverState *bs);
>  BlockDriverState *bdrv_snapshots(void);