Re: [Qemu-devel] [PATCH V4] block: Add BlockDriver.bdrv_check_ext_snapshot.

[Max Reitz <mreitz@redhat.com>]

On 2013-10-02 14:33, Benoît Canet wrote:
> This field is used by blkverify to disable external snapshots creation.
> I will also be used by block filters like quorum to disable external snapshots
> creation.
>
> Signed-off-by: Benoit Canet <benoit@irqsave.net>
> ---
>   block.c                   | 17 +++++++++++++++++
>   block/blkverify.c         |  2 ++
>   blockdev.c                |  5 +++++
>   include/block/block.h     | 14 ++++++++++++++
>   include/block/block_int.h |  6 ++++++
>   5 files changed, 44 insertions(+)
>
> diff --git a/block.c b/block.c
> index 93e113a..e891522 100644
> --- a/block.c
> +++ b/block.c
> @@ -4632,3 +4632,20 @@ int bdrv_amend_options(BlockDriverState *bs, QEMUOptionParameter *options)
>       }
>       return bs->drv->bdrv_amend_options(bs, options);
>   }
> +
> +ExtSnapshotPerm bdrv_check_ext_snapshot(BlockDriverState *bs)
> +{
> +    /* external snashots are allowed by defaults */
I don't really know whether it should rather be "by default", but it 
certainly should be s/snashots/snapshots/. ;)
Also, I'd move this comment below the if statements and above the return 
EXT_SNAPSHOT_ALLOWED.

> +    if (bs->drv->bdrv_check_ext_snapshot) {
> +        return bs->drv->bdrv_check_ext_snapshot(bs);
> +    }
> +    if (bs->file && bs->file->drv && bs->file->drv->bdrv_check_ext_snapshot) {
> +        return bs->file->drv->bdrv_check_ext_snapshot(bs);
> +    }
> +    return EXT_SNAPSHOT_ALLOWED;
> +}
> +
> +ExtSnapshotPerm bdrv_check_ext_snapshot_forbidden(BlockDriverState *bs)
> +{
> +    return EXT_SNAPSHOT_FORBIDDEN;
> +}
> diff --git a/block/blkverify.c b/block/blkverify.c
> index 2077d8a..b64c638 100644
> --- a/block/blkverify.c
> +++ b/block/blkverify.c
> @@ -313,6 +313,8 @@ static BlockDriver bdrv_blkverify = {
>       .bdrv_aio_readv         = blkverify_aio_readv,
>       .bdrv_aio_writev        = blkverify_aio_writev,
>       .bdrv_aio_flush         = blkverify_aio_flush,
> +
> +    .bdrv_check_ext_snapshot = bdrv_check_ext_snapshot_forbidden,
>   };
>   
>   static void bdrv_blkverify_init(void)
> diff --git a/blockdev.c b/blockdev.c
> index 8aa66a9..92029d8 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -1131,6 +1131,11 @@ static void external_snapshot_prepare(BlkTransactionState *common,
>           }
>       }
>   
> +    if (bdrv_check_ext_snapshot(state->old_bs) != EXT_SNAPSHOT_ALLOWED) {
> +        error_set(errp, QERR_FEATURE_DISABLED, "snapshot");
> +        return;
> +    }
> +
>       flags = state->old_bs->open_flags;
>   
>       /* create new image w/backing file */
> diff --git a/include/block/block.h b/include/block/block.h
> index f808550..2bf0e12 100644
> --- a/include/block/block.h
> +++ b/include/block/block.h
> @@ -244,6 +244,20 @@ int bdrv_check(BlockDriverState *bs, BdrvCheckResult *res, BdrvCheckMode fix);
>   
>   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_FORBIDEN if external snapshot is forbiden
s/FORBIDEN/FORBIDDEN/, s/forbiden/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);
> +
>   /* async block I/O */
>   typedef void BlockDriverDirtyHandler(BlockDriverState *bs, int64_t sector,
>                                        int sector_num);
> diff --git a/include/block/block_int.h b/include/block/block_int.h
> index 211087a..e6a14ae 100644
> --- a/include/block/block_int.h
> +++ b/include/block/block_int.h
> @@ -67,6 +67,12 @@ typedef struct BdrvTrackedRequest {
>   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
> +     */
> +    ExtSnapshotPerm (*bdrv_check_ext_snapshot)(BlockDriverState *bs);
> +
>       int (*bdrv_probe)(const uint8_t *buf, int buf_size, const char *filename);
>       int (*bdrv_probe_device)(const char *filename);
>   

Aside from the misspellings (and regardless of whether you decide to 
move the comment or not):

Reviewed-by: Max Reitz <mreitz@redhat.com>