On 08.07.20 20:24, Andrey Shinkevich wrote:
> On 25.06.2020 18:21, Max Reitz wrote:
>> Places that use patterns like
>>
>>      if (bs->drv->is_filter && bs->file) {
>>          ... something about bs->file->bs ...
>>      }
>>
>> should be
>>
>>      BlockDriverState *filtered = bdrv_filter_bs(bs);
>>      if (filtered) {
>>          ... something about @filtered ...
>>      }
>>
>> instead.
>>
>> Signed-off-by: Max Reitz <mreitz@redhat.com>
>> ---
>>   block.c                        | 31 ++++++++++++++++++++-----------
>>   block/io.c                     |  7 +++++--
>>   migration/block-dirty-bitmap.c |  8 +-------
>>   3 files changed, 26 insertions(+), 20 deletions(-)
>>
> ...
>> diff --git a/block/io.c b/block/io.c
>> index df8f2a98d4..385176b331 100644
>> --- a/block/io.c
>> +++ b/block/io.c
>> @@ -3307,6 +3307,7 @@ int coroutine_fn bdrv_co_truncate(BdrvChild
>> *child, int64_t offset, bool exact,
>>                                     Error **errp)
>>   {
>>       BlockDriverState *bs = child->bs;
>> +    BdrvChild *filtered;
>>       BlockDriver *drv = bs->drv;
>>       BdrvTrackedRequest req;
>>       int64_t old_size, new_bytes;
>> @@ -3358,6 +3359,8 @@ int coroutine_fn bdrv_co_truncate(BdrvChild
>> *child, int64_t offset, bool exact,
>>           goto out;
>>       }
>>   +    filtered = bdrv_filter_child(bs);
>> +
> 
> Isn't better to have this initialization right before the relevant
> if/else block?

Hm, well, yes.  In this case, though, maybe not.  Patch 16 will add
another BdrvChild to be initialized here (@backing), and we need to
initialize that one here.  So I felt it made sense to group them together.

They got split up when I decided to put @filtered into this patch and
@backing into its own.  So now it may look a bit weird, but I feel like
after patch 16 it makes sense.

(I’m indifferent, basically.)

Max