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

[Max Reitz]

On 06.05.20 18:37, Kevin Wolf wrote:
> 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 <address@hidden>
>> Reviewed-by: Eric Blake <address@hidden>
>> ---
>>  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...)

I’ll pull in “block: Mark commit and mirror as filter drivers” from the
main series then.

>>  /*
>>   * 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?

It’d be indeed.

Max

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