Re: [Qemu-devel] [PATCH v2 2/3] block-backend: add drained_begin / drained_end ops

[Jeff Cody]

On Thu, Mar 16, 2017 at 05:23:50PM -0400, John Snow wrote:
> Allow block backends to forward drain requests to their devices/users.
> The initial intended purpose for this patch is to allow BBs to forward
> requests along to BlockJobs, which will want to pause if their associated
> BB has entered a drained region.
> 
> Signed-off-by: John Snow <address@hidden>
> ---
>  block/block-backend.c          | 24 ++++++++++++++++++++++--
>  include/sysemu/block-backend.h |  8 ++++++++
>  2 files changed, 30 insertions(+), 2 deletions(-)
> 
> diff --git a/block/block-backend.c b/block/block-backend.c
> index 5742c09..dec4a1c 100644
> --- a/block/block-backend.c
> +++ b/block/block-backend.c
> @@ -65,6 +65,8 @@ struct BlockBackend {
>      bool allow_write_beyond_eof;
>  
>      NotifierList remove_bs_notifiers, insert_bs_notifiers;
> +
> +    int quiesce_counter;
>  };
>  
>  typedef struct BlockBackendAIOCB {
> @@ -699,12 +701,17 @@ void blk_set_dev_ops(BlockBackend *blk, const 
> BlockDevOps *ops,
>                       void *opaque)
>  {
>      /* All drivers that use blk_set_dev_ops() are qdevified and we want to 
> keep
> -     * it that way, so we can assume blk->dev is a DeviceState if 
> blk->dev_ops
> -     * is set. */
> +     * it that way, so we can assume blk->dev, if present, is a DeviceState 
> if
> +     * blk->dev_ops is set. Non-device users may use dev_ops without device. 
> */
>      assert(!blk->legacy_dev);
>  
>      blk->dev_ops = ops;
>      blk->dev_opaque = opaque;
> +
> +    /* Are we currently quiesced? Should we enforce this right now? */
> +    if (blk->quiesce_counter && ops->drained_begin) {
> +        ops->drained_begin(opaque);
> +    }
>  }
>  
>  /*
> @@ -1870,6 +1877,12 @@ static void blk_root_drained_begin(BdrvChild *child)
>  {
>      BlockBackend *blk = child->opaque;
>  
> +    if (++blk->quiesce_counter == 1) {
> +        if (blk->dev_ops && blk->dev_ops->drained_begin) {
> +            blk->dev_ops->drained_begin(blk->dev_opaque);
> +        }
> +    }
> +
>      /* Note that blk->root may not be accessible here yet if we are just
>       * attaching to a BlockDriverState that is drained. Use child instead. */
>  
> @@ -1881,7 +1894,14 @@ static void blk_root_drained_begin(BdrvChild *child)
>  static void blk_root_drained_end(BdrvChild *child)
>  {
>      BlockBackend *blk = child->opaque;
> +    assert(blk->quiesce_counter);
>  
>      assert(blk->public.io_limits_disabled);
>      --blk->public.io_limits_disabled;
> +
> +    if (--blk->quiesce_counter == 0) {
> +        if (blk->dev_ops && blk->dev_ops->drained_end) {
> +              blk->dev_ops->drained_end(blk->dev_opaque);
> +        }
> +    }
>  }
> diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h
> index 096c17f..7462228 100644
> --- a/include/sysemu/block-backend.h
> +++ b/include/sysemu/block-backend.h
> @@ -58,6 +58,14 @@ typedef struct BlockDevOps {
>       * Runs when the size changed (e.g. monitor command block_resize)
>       */
>      void (*resize_cb)(void *opaque);
> +    /*
> +     * Runs when the backend receives a drain request.
> +     */
> +    void (*drained_begin)(void *opaque);
> +    /*
> +     * Runs when the backend's last drain request ends.
> +     */
> +    void (*drained_end)(void *opaque);
>  } BlockDevOps;
>  
>  /* This struct is embedded in (the private) BlockBackend struct and contains
> -- 
> 2.9.3
>

Reviewed-by: Jeff Cody <address@hidden>