Re: [Qemu-devel] [PATCH v14 06/14] block: Add backing_blocker in BlockDriverState

[Jeff Cody <jcody@redhat.com>]

On Wed, Feb 19, 2014 at 09:42:23PM +0800, Fam Zheng wrote:
> This makes use of op_blocker and blocks all the operations except for
> commit target, on each BlockDriverState->backing_hd.
> 
> The asserts for op_blocker in bdrv_swap are removed because with this
> change, the target of block commit has at least the backing blocker of
> its child, so the assertion is not true. Callers should do their check.
> 
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  block.c                   | 19 +++++++++++++++----
>  include/block/block_int.h |  3 +++
>  2 files changed, 18 insertions(+), 4 deletions(-)
> 
> diff --git a/block.c b/block.c
> index dec44d4..95d8c1f 100644
> --- a/block.c
> +++ b/block.c
> @@ -1044,19 +1044,33 @@ fail:
>  void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd)
>  {
>      if (bs->backing_hd) {
> +        assert(error_is_set(&bs->backing_blocker));

When I run block-commit, on either the active or non-active layer, I
get an assertion here.  The qemu-iotests do not catch it, and I
presume it is because happens a couple of seconds or so after the
success message is returned over QMP.

> +        bdrv_op_unblock_all(bs->backing_hd, bs->backing_blocker);
>          bdrv_unref(bs->backing_hd);
> +    } else if (backing_hd) {
> +        error_setg(&bs->backing_blocker,
> +                   "device is used as backing hd of '%s'",
> +                   bs->device_name);
>      }
>  
>      bs->backing_hd = backing_hd;
>      if (!backing_hd) {
>          bs->backing_file[0] = '\0';
>          bs->backing_format[0] = '\0';
> +        if (error_is_set(&bs->backing_blocker)) {
> +            error_free(bs->backing_blocker);
> +        }
>          goto out;
>      }
>      pstrcpy(bs->backing_file, sizeof(bs->backing_file), backing_hd->filename);
>      pstrcpy(bs->backing_format, sizeof(bs->backing_format),
>              backing_hd->drv ? backing_hd->drv->format_name : "");
>      bdrv_ref(bs->backing_hd);
> +
> +    bdrv_op_block_all(bs->backing_hd, bs->backing_blocker);
> +    /* Otherwise we won't be able to commit due to check in bdrv_commit */
> +    bdrv_op_unblock(bs->backing_hd, BLOCK_OP_TYPE_COMMIT,
> +                    bs->backing_blocker);
>  out:
>      bdrv_refresh_limits(bs);
>  }
> @@ -1696,8 +1710,7 @@ void bdrv_close(BlockDriverState *bs)
>  
>      if (bs->drv) {
>          if (bs->backing_hd) {
> -            bdrv_unref(bs->backing_hd);
> -            bs->backing_hd = NULL;
> +            bdrv_set_backing_hd(bs, NULL);
>          }
>          bs->drv->bdrv_close(bs);
>          g_free(bs->opaque);
> @@ -1899,7 +1912,6 @@ void bdrv_swap(BlockDriverState *bs_new, BlockDriverState *bs_old)
>      assert(QLIST_EMPTY(&bs_new->dirty_bitmaps));
>      assert(bs_new->job == NULL);
>      assert(bs_new->dev == NULL);
> -    assert(bdrv_op_blocker_is_empty(bs_new));
>      assert(bs_new->io_limits_enabled == false);
>      assert(!throttle_have_timer(&bs_new->throttle_state));
>  
> @@ -1918,7 +1930,6 @@ void bdrv_swap(BlockDriverState *bs_new, BlockDriverState *bs_old)
>      /* Check a few fields that should remain attached to the device */
>      assert(bs_new->dev == NULL);
>      assert(bs_new->job == NULL);
> -    assert(bdrv_op_blocker_is_empty(bs_new));
>      assert(bs_new->io_limits_enabled == false);
>      assert(!throttle_have_timer(&bs_new->throttle_state));
>  
> diff --git a/include/block/block_int.h b/include/block/block_int.h
> index 1d3f76f..1f4f78b 100644
> --- a/include/block/block_int.h
> +++ b/include/block/block_int.h
> @@ -369,6 +369,9 @@ struct BlockDriverState {
>      BlockJob *job;
>  
>      QDict *options;
> +
> +    /* The error object in use for blocking operations on backing_hd */
> +    Error *backing_blocker;
>  };
>  
>  int get_tmp_filename(char *filename, int size);
> -- 
> 1.8.5.4
> 
>