Re: [Qemu-devel] [PATCH 11/12] block: Use normal drain for bdrv_set_aio_context()

[Eric Blake]

On 2/18/19 10:18 AM, Kevin Wolf wrote:
> Now that bdrv_set_aio_context() works inside drained sections, it can
> also use the real drain function instead of open coding something
> similar.
> 
> Signed-off-by: Kevin Wolf <address@hidden>
> ---
>  block.c | 14 +++++---------
>  1 file changed, 5 insertions(+), 9 deletions(-)
> 
> diff --git a/block.c b/block.c
> index aefb5701f5..7024172db8 100644
> --- a/block.c
> +++ b/block.c
> @@ -5268,18 +5268,15 @@ void bdrv_attach_aio_context(BlockDriverState *bs,
>      bs->walking_aio_notifiers = false;
>  }
>  
> +/* The caller must own the AioContext lock for the old AioContext of bs, but 
> it
> + * must not own the AioContext lock for new_context. */

Is this comment still accurate, given

>  void bdrv_set_aio_context(BlockDriverState *bs, AioContext *new_context)
>  {
> -    AioContext *ctx = bdrv_get_aio_context(bs);
> -
> -    if (ctx == new_context) {
> +    if (bdrv_get_aio_context(bs) == new_context) {
>          return;
>      }

the short-circuiting when the old context is the new context?

>  
> -    aio_disable_external(ctx);
> -    bdrv_parent_drained_begin(bs, NULL, false);
> -    bdrv_drain(bs); /* ensure there are no in-flight requests */
> -
> +    bdrv_drained_begin(bs);
>      bdrv_detach_aio_context(bs);
>  
>      /* This function executes in the old AioContext so acquire the new one in
> @@ -5287,8 +5284,7 @@ void bdrv_set_aio_context(BlockDriverState *bs, 
> AioContext *new_context)
>       */
>      aio_context_acquire(new_context);
>      bdrv_attach_aio_context(bs, new_context);
> -    bdrv_parent_drained_end(bs, NULL, false);
> -    aio_enable_external(ctx);
> +    bdrv_drained_end(bs);
>      aio_context_release(new_context);
>  }
>  
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org