Re: [Qemu-block] [PATCH 16/19] block: Allow graph changes in subtree drained section

[Paolo Bonzini]

On 20/12/2017 11:34, Kevin Wolf wrote:
>      .inherit_options = bdrv_inherited_options,
>      .drained_begin   = bdrv_child_cb_drained_begin,
>      .drained_end     = bdrv_child_cb_drained_end,
> +    .attach          = bdrv_child_cb_attach,
> +    .detach          = bdrv_child_cb_detach,
>      .inactivate      = bdrv_child_cb_inactivate,
>  };
>  
> @@ -911,6 +933,8 @@ const BdrvChildRole child_format = {
>      .inherit_options = bdrv_inherited_fmt_options,
>      .drained_begin   = bdrv_child_cb_drained_begin,
>      .drained_end     = bdrv_child_cb_drained_end,
> +    .attach          = bdrv_child_cb_attach,
> +    .detach          = bdrv_child_cb_detach,
>      .inactivate      = bdrv_child_cb_inactivate,

Is there any case of a BdrvChildRole that doesn't want these callbacks?
Maybe the functions should be called after ->attach and before ->detach
(e.g. bdrv_{,un}apply_subtree_drain), rather than modifying the
BdrvChildRole implementations.

Then they can be put in block/io.c, and bdrv_do_drained_* can remain
static.  (I would also consider extracting block/drain.c, but it is
painful to do it now that you have this nice series---so let's do it after).

Paolo