Re: [Qemu-devel] [PATCH v20 04/15] block: Move op_blocker check from block_job_create to its caller

[Jeff Cody]

On Tue, May 20, 2014 at 02:04:29PM +0800, Fam Zheng wrote:
> It makes no sense to check for "any" blocker on bs, we are here only
> because of the mechanical conversion from in_use to op_blockers. Remove
> it now, and let the callers check specific operation types. Backup and
> mirror already have it, add checker to stream and commit.
> 
> Signed-off-by: Fam Zheng <address@hidden>
> Reviewed-by: Benoit Canet <address@hidden>
> Reviewed-by: Jeff Cody <address@hidden>
> ---
>  blockdev.c | 8 ++++++++
>  blockjob.c | 2 +-
>  2 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/blockdev.c b/blockdev.c
> index 5d950fa..21fc55b 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -1850,6 +1850,10 @@ void qmp_block_stream(const char *device, bool 
> has_base,
>          return;
>      }
>  
> +    if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_STREAM, errp)) {
> +        return;
> +    }
> +
>      if (base) {
>          base_bs = bdrv_find_backing_image(bs, base);
>          if (base_bs == NULL) {
> @@ -1894,6 +1898,10 @@ void qmp_block_commit(const char *device,
>          return;
>      }
>  
> +    if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_COMMIT, errp)) {
> +        return;
> +    }
> +

Is the blocker intended to operate at the device level, i.e. to mark a
whole chain as 'blocked' for one or more operations?  Or, is it
intended to block at the singular BDS level (the commit message in
patch 2 implies this meaning)?

More to the point: if a BDS is marked as blocked, does that also imply
all of the images in its backing chain are also considered blocked?
Conversely, if a BDS is *not* marked as blocked, does that mean all of
its backing chain is also unblocked?

If the answer to the two questions above is 'yes', then the
bdrv_op_block/unblock functions should probably operate recursively
down the chain to the bottom-most backing file.

If the answer is 'no', then for some operations like stream and commit
(and probably others), don't we also need to worry about the blocker
state of a lot more images in the chain?


>      /* default top_bs is the active layer */
>      top_bs = bs;
>  
> diff --git a/blockjob.c b/blockjob.c
> index 60e72f5..7d84ca1 100644
> --- a/blockjob.c
> +++ b/blockjob.c
> @@ -41,7 +41,7 @@ void *block_job_create(const BlockJobDriver *driver, 
> BlockDriverState *bs,
>  {
>      BlockJob *job;
>  
> -    if (bs->job || !bdrv_op_blocker_is_empty(bs)) {
> +    if (bs->job) {
>          error_set(errp, QERR_DEVICE_IN_USE, bdrv_get_device_name(bs));
>          return NULL;
>      }
> -- 
> 1.9.2
>