Re: [PATCH 19/24] block: Introduce bdrv_co_change_backing_file()

[Eric Blake]

On Fri, Oct 27, 2023 at 05:53:28PM +0200, Kevin Wolf wrote:
> bdrv_change_backing_file() is called both inside and outside coroutine
> context. This makes it difficult for it to take the graph lock
> internally. It also means that driver implementations need to be able to
> run outside of coroutines, too. Switch it to the usual model with a
> coroutine based implementation and a co_wrapper instead. The new
> function is marked GRAPH_RDLOCK.
> 
> As the co_wrapper now runs the function in the AioContext of the node
> (as it should always have done), this is not GLOBAL_STATE_CODE() any
> more.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  include/block/block-global-state.h |  3 +-
>  include/block/block-io.h           |  8 ++++
>  include/block/block_int-common.h   |  5 ++-
>  block.c                            | 11 ++---
>  block/qcow2.c                      | 18 +++++----
>  block/qed.c                        | 64 +++++++++++++++---------------
>  tests/unit/test-bdrv-drain.c       |  8 ++--
>  7 files changed, 65 insertions(+), 52 deletions(-)
> 
> +++ b/block/qcow2.c
> @@ -6155,9 +6159,9 @@ BlockDriver bdrv_qcow2 = {
>      .bdrv_co_save_vmstate   = qcow2_co_save_vmstate,
>      .bdrv_co_load_vmstate   = qcow2_co_load_vmstate,
>  
> -    .is_format                  = true,
> -    .supports_backing           = true,
> -    .bdrv_change_backing_file   = qcow2_change_backing_file,
> +    .is_format                      = true,
> +    .supports_backing               = true,
> +    .bdrv_co_change_backing_file    = qcow2_co_change_backing_file,
>  
>      .bdrv_refresh_limits        = qcow2_refresh_limits,
>      .bdrv_co_invalidate_cache   = qcow2_co_invalidate_cache,

Here, you only realigned = on a portion of the initializer...

> diff --git a/block/qed.c b/block/qed.c
> index 686ad711f7..996aa384fe 100644
> --- a/block/qed.c
> +++ b/block/qed.c
>  static BlockDriver bdrv_qed = {
> -    .format_name              = "qed",
> -    .instance_size            = sizeof(BDRVQEDState),
> -    .create_opts              = &qed_create_opts,
> -    .is_format                = true,
> -    .supports_backing         = true,
> -
> -    .bdrv_probe               = bdrv_qed_probe,

...while here, you are doing it on the entire block.  This shows why I
personally dislike aligning =, but I tolerate it when it is already
prevailing style.  Still, it feels weird to be inconsistent within the
same patch.

At any rate, that's cosmetic, and not a correctness issue.  Up to you
if you want to ignore my commentary in this case.

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization:  qemu.org | libguestfs.org