Re: [Qemu-devel] [PATCH V6 5/8] block: Create authorizations mechanism for external snapshot and resize.

[Jeff Cody]

On Thu, Jan 23, 2014 at 09:31:36PM +0100, Benoît Canet wrote:
> From: Benoît Canet <address@hidden>
> 
> Signed-off-by: Benoit Canet <address@hidden>
> ---
>  block.c                   | 65 
> ++++++++++++++++++++++++++++++++++++++++-------
>  block/blkverify.c         |  2 +-
>  blockdev.c                |  2 +-
>  include/block/block.h     | 20 +++++++--------
>  include/block/block_int.h | 12 ++++++---
>  5 files changed, 77 insertions(+), 24 deletions(-)
> 
> diff --git a/block.c b/block.c
> index e1bc732..3e0994b 100644
> --- a/block.c
> +++ b/block.c
> @@ -5088,21 +5088,68 @@ int bdrv_amend_options(BlockDriverState *bs, 
> QEMUOptionParameter *options)
>      return bs->drv->bdrv_amend_options(bs, options);
>  }
>  
> -ExtSnapshotPerm bdrv_check_ext_snapshot(BlockDriverState *bs)
> +/* Used to recurse on single child block filters.
> + * Single child block filter will store their child in bs->file.
> + */
> +bool bdrv_generic_is_first_non_filter(BlockDriverState *bs,
> +                                      BlockDriverState *candidate)
>  {
> -    if (bs->drv->bdrv_check_ext_snapshot) {
> -        return bs->drv->bdrv_check_ext_snapshot(bs);
> +    if (!bs->drv) {
> +        return false;
> +    }
> +
> +    if (!bs->drv->authorizations[BS_IS_A_FILTER]) {
> +        if (bs == candidate) {
> +            return true;
> +        } else {
> +            return false;
> +        }

This seems to break external snapshots; after this patch, I can no
longer perform live ext snapshots (on qcow2, raw, etc..), unless I am
doing something incorrectly.

Instead of checking for bs == candidate, was it intended to check to
see if !strcmp(bs->filename, candidiate->filename) was true?

Or maybe it is how bdrv_is_first_non_filter() is called (see below):

<snip>

> diff --git a/blockdev.c b/blockdev.c
> index 3c27911..8f95c7f 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -1250,7 +1250,7 @@ static void 
> external_snapshot_prepare(BlkTransactionState *common,
>          }
>      }
>  
> -    if (bdrv_check_ext_snapshot(state->old_bs) != EXT_SNAPSHOT_ALLOWED) {
> +    if (!bdrv_is_first_non_filter(state->old_bs)) {

Should this be: !bdrv_is_first_non_filter(state->old_bs->file)?



>          error_set(errp, QERR_FEATURE_DISABLED, "snapshot");
>          return;
>      }
> diff --git a/include/block/block.h b/include/block/block.h
> index b4a77e6..59d9f12 100644
> --- a/include/block/block.h
> +++ b/include/block/block.h
> @@ -287,16 +287,16 @@ int bdrv_amend_options(BlockDriverState *bs_new, 
> QEMUOptionParameter *options);
>  /* external snapshots */
>  
>  typedef enum {
> -    EXT_SNAPSHOT_ALLOWED,
> -    EXT_SNAPSHOT_FORBIDDEN,
> -} ExtSnapshotPerm;
> -
> -/* return EXT_SNAPSHOT_ALLOWED if external snapshot is allowed
> - * return EXT_SNAPSHOT_FORBIDDEN if external snapshot is forbidden
> - */
> -ExtSnapshotPerm bdrv_check_ext_snapshot(BlockDriverState *bs);
> -/* helper used to forbid external snapshots like in blkverify */
> -ExtSnapshotPerm bdrv_check_ext_snapshot_forbidden(BlockDriverState *bs);
> +    BS_IS_A_FILTER,
> +    BS_FILTER_PASS_DOWN,
> +    BS_AUTHORIZATION_COUNT,
> +} BsAuthorization;
> +
> +bool bdrv_generic_is_first_non_filter(BlockDriverState *bs,
> +                                      BlockDriverState *candidate);
> +bool bdrv_recurse_is_first_non_filter(BlockDriverState *bs,
> +                                      BlockDriverState *candidate);
> +bool bdrv_is_first_non_filter(BlockDriverState *candidate);
>  
>  /* async block I/O */
>  typedef void BlockDriverDirtyHandler(BlockDriverState *bs, int64_t sector,
> diff --git a/include/block/block_int.h b/include/block/block_int.h
> index f3f518c..611a955 100644
> --- a/include/block/block_int.h
> +++ b/include/block/block_int.h
> @@ -69,10 +69,16 @@ struct BlockDriver {
>      const char *format_name;
>      int instance_size;
>  
> -    /* if not defined external snapshots are allowed
> -     * future block filters will query their children to build the response
> +    /* this table of boolean contains authorizations for the block 
> operations */
> +    bool authorizations[BS_AUTHORIZATION_COUNT];
> +    /* for snapshots complex block filter like Quorum can implement the
> +     * following recursive callback instead of BS_IS_A_FILTER.
> +     * It's purpose is to recurse on the filter children while calling
> +     * bdrv_recurse_is_first_non_filter on them.
> +     * For a sample implementation look in the future Quorum block filter.
>       */
> -    ExtSnapshotPerm (*bdrv_check_ext_snapshot)(BlockDriverState *bs);
> +    bool (*bdrv_recurse_is_first_non_filter)(BlockDriverState *bs,
> +                                             BlockDriverState *candidate);
>  
>      int (*bdrv_probe)(const uint8_t *buf, int buf_size, const char 
> *filename);
>      int (*bdrv_probe_device)(const char *filename);
> -- 
> 1.8.3.2
> 
>