Re: [Qemu-devel] [PATCH v2 11/11] block: Block "device IO" during bdrv_drain and bdrv_drain_all

[Paolo Bonzini <pbonzini@redhat.com>]

On 13/05/2015 19:28, Fam Zheng wrote:
> We don't want new requests from guest, so block the operation around the
> nested poll.
> 
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  block/io.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/block/io.c b/block/io.c
> index 1ce62c4..d369de3 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -289,9 +289,15 @@ static bool bdrv_drain_one(BlockDriverState *bs)
>   */
>  void bdrv_drain(BlockDriverState *bs)
>  {
> +    Error *blocker = NULL;
> +
> +    error_setg(&blocker, "bdrv_drain in progress");
> +    bdrv_op_block(bs, BLOCK_OP_TYPE_DEVICE_IO, blocker);
>      while (bdrv_drain_one(bs)) {
>          /* Keep iterating */
>      }
> +    bdrv_op_unblock(bs, BLOCK_OP_TYPE_DEVICE_IO, blocker);
> +    error_free(blocker);
>  }
>  
>  /*
> @@ -311,6 +317,9 @@ void bdrv_drain_all(void)
>      /* Always run first iteration so any pending completion BHs run */
>      bool busy = true;
>      BlockDriverState *bs = NULL;
> +    Error *blocker = NULL;
> +
> +    error_setg(&blocker, "bdrv_drain_all in progress");
>  
>      while ((bs = bdrv_next(bs))) {
>          AioContext *aio_context = bdrv_get_aio_context(bs);
> @@ -319,6 +328,7 @@ void bdrv_drain_all(void)
>          if (bs->job) {
>              block_job_pause(bs->job);
>          }
> +        bdrv_op_block(bs, BLOCK_OP_TYPE_DEVICE_IO, blocker);
>          aio_context_release(aio_context);
>      }
>  
> @@ -343,8 +353,10 @@ void bdrv_drain_all(void)
>          if (bs->job) {
>              block_job_resume(bs->job);
>          }
> +        bdrv_op_unblock(bs, BLOCK_OP_TYPE_DEVICE_IO, blocker);
>          aio_context_release(aio_context);
>      }
> +    error_free(blocker);
>  }
>  
>  /**
> 

I think this isn't enough.  It's the callers of bdrv_drain and
bdrv_drain_all that need to block before drain and unblock before
aio_context_release.

Paolo