Re: [PATCH v3 22/33] block: Make backing files child_of_bds children

[Kevin Wolf <kwolf@redhat.com>]

Am 18.02.2020 um 13:42 hat Max Reitz geschrieben:
> Make all parents of backing files pass the appropriate BdrvChildRole.
> By doing so, we can switch their BdrvChildClass over to the generic
> child_of_bds, which will do the right thing when given a correct
> BdrvChildRole.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> ---
>  block.c                 | 26 ++++++++++++++++++++------
>  block/backup-top.c      |  2 +-
>  block/vvfat.c           |  3 ++-
>  tests/test-bdrv-drain.c | 13 +++++++------
>  4 files changed, 30 insertions(+), 14 deletions(-)
> 
> diff --git a/block.c b/block.c
> index 43df38ca30..31affcb4ee 100644
> --- a/block.c
> +++ b/block.c
> @@ -2770,6 +2770,20 @@ static bool bdrv_inherits_from_recursive(BlockDriverState *child,
>      return child != NULL;
>  }
>  
> +/*
> + * Return the BdrvChildRole for @bs's backing child.  bs->backing is
> + * mostly used for COW backing children (role = COW), but also for
> + * filtered children (role = FILTERED | PRIMARY).
> + */
> +static BdrvChildRole bdrv_backing_role(BlockDriverState *bs)
> +{
> +    if (bs->drv && bs->drv->is_filter) {
> +        return BDRV_CHILD_FILTERED | BDRV_CHILD_PRIMARY;
> +    } else {
> +        return BDRV_CHILD_COW;
> +    }
> +}

bdrv_mirror_top and bdrv_commit_top don't set .is_filter, so it will
return the wrong role for them. (They also don't set .supports_backing,
so grepping for that wouldn't help...)

>  /*
>   * Sets the backing file link of a BDS. A new reference is created; callers
>   * which don't need their own reference any more must call bdrv_unref().
> @@ -2797,8 +2811,8 @@ void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd,
>          goto out;
>      }
>  
> -    bs->backing = bdrv_attach_child(bs, backing_hd, "backing", &child_backing,
> -                                    0, errp);
> +    bs->backing = bdrv_attach_child(bs, backing_hd, "backing", &child_of_bds,
> +                                    bdrv_backing_role(bs), errp);
>      /* If backing_hd was already part of bs's backing chain, and
>       * inherits_from pointed recursively to bs then let's update it to
>       * point directly to bs (else it will become NULL). */
> @@ -2895,7 +2909,7 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *parent_options,
>      }
>  
>      backing_hd = bdrv_open_inherit(backing_filename, reference, options, 0, bs,
> -                                   &child_backing, 0, errp);
> +                                   &child_of_bds, BDRV_CHILD_COW, errp);

Wouldn't it be more consistent to use bdrv_backing_role() here, too?

Kevin