Re: [Qemu-devel] [PATCH RFC 2/7] block-backend: Introduce blk_root() helper

[Changlong Xie]

I know you need blk->root in the next patch, but we strongly don't 
recommend your current solution.  Please refer Kevin's cf2ab8fc

1409     /* XXX Ugly way to get blk->root, but that's a feature, not a 
bug. This
1410      * hack makes it obvious that vhdx_write_header() bypasses the 
BlockBackend
1411      * here, which it really shouldn't be doing. */
1412     child = QLIST_FIRST(&bs->parents);
1413     assert(!QLIST_NEXT(child, next_parent));

Then you can drop this commit.

On 10/20/2016 09:57 PM, zhanghailiang wrote:
> With this helper function, we can get the BdrvChild struct
> from BlockBackend
>
> Signed-off-by: zhanghailiang <address@hidden>
> ---
>   block/block-backend.c          | 5 +++++
>   include/sysemu/block-backend.h | 1 +
>   2 files changed, 6 insertions(+)
>
> diff --git a/block/block-backend.c b/block/block-backend.c
> index 1a724a8..66387f0 100644
> --- a/block/block-backend.c
> +++ b/block/block-backend.c
> @@ -389,6 +389,11 @@ BlockDriverState *blk_bs(BlockBackend *blk)
>       return blk->root ? blk->root->bs : NULL;
>   }
>
> +BdrvChild *blk_root(BlockBackend *blk)
> +{
> +    return blk->root;
> +}
> +
>   static BlockBackend *bdrv_first_blk(BlockDriverState *bs)
>   {
>       BdrvChild *child;
> diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h
> index b07159b..867f9f5 100644
> --- a/include/sysemu/block-backend.h
> +++ b/include/sysemu/block-backend.h
> @@ -99,6 +99,7 @@ void blk_remove_bs(BlockBackend *blk);
>   void blk_insert_bs(BlockBackend *blk, BlockDriverState *bs);
>   bool bdrv_has_blk(BlockDriverState *bs);
>   bool bdrv_is_root_node(BlockDriverState *bs);
> +BdrvChild *blk_root(BlockBackend *blk);
>
>   void blk_set_allow_write_beyond_eof(BlockBackend *blk, bool allow);
>   void blk_iostatus_enable(BlockBackend *blk);