Re: [Qemu-block] [PATCH v3 07/16] block: Convert bs->backing_hd to BdrvChild

[Jeff Cody]

On Fri, Oct 09, 2015 at 02:15:32PM +0200, Kevin Wolf wrote:
> This is the final step in converting all of the BlockDriverState
> pointers that block drivers use to BdrvChild.
> 
> After this patch, bs->children contains the full list of child nodes
> that are referenced by a given BDS, and these children are only
> referenced through BdrvChild, so that updating the pointer in there is
> enough for changing edges in the graph.
> 
> Signed-off-by: Kevin Wolf <address@hidden>
> ---
>  block.c                   | 105 
> +++++++++++++++++++++++-----------------------
>  block/io.c                |  24 +++++------
>  block/mirror.c            |   6 +--
>  block/qapi.c              |   8 ++--
>  block/qcow.c              |   4 +-
>  block/qcow2-cluster.c     |   4 +-
>  block/qcow2.c             |   6 +--
>  block/qed.c               |  12 +++---
>  block/stream.c            |   8 ++--
>  block/vmdk.c              |  21 +++++-----
>  block/vvfat.c             |   6 +--
>  blockdev.c                |   4 +-
>  include/block/block_int.h |  12 ++++--
>  qemu-img.c                |   4 +-
>  14 files changed, 115 insertions(+), 109 deletions(-)
> 

[...]

> diff --git a/include/block/block_int.h b/include/block/block_int.h
> index 98936c9..90971c0 100644
> --- a/include/block/block_int.h
> +++ b/include/block/block_int.h
> @@ -378,8 +378,7 @@ struct BlockDriverState {
>      QDict *full_open_options;
>      char exact_filename[PATH_MAX];
>  
> -    BlockDriverState *backing_hd;
> -    BdrvChild *backing_child;
> +    BdrvChild *backing;
>      BdrvChild *file;
>  
>      NotifierList close_notifiers;
> @@ -458,6 +457,11 @@ struct BlockDriverState {
>      NotifierWithReturn write_threshold_notifier;
>  };
>  
> +static inline BlockDriverState *backing_bs(BlockDriverState *bs)
> +{
> +    return bs->backing ? bs->backing->bs : NULL;
> +}
> +

Is there a good guideline regarding when you prefer backing_bs() to be
used, over accessing bs->backing->bs directly?  There seems to be a
lot of mixed usage left in this patch, and I'm not sure if I am just
missing the intended distinction.

Thanks,
Jeff