Re: [Qemu-devel] [Qemu-block] [PATCH] block/qcow2: fix logic around dirty_bitmaps_loaded

[John Snow <jsnow@redhat.com>]

On 06/12/2018 06:11 PM, John Snow wrote:
> 
> 
> On 06/12/2018 01:26 PM, Vladimir Sementsov-Ogievskiy wrote:
>> First: this variable was introduced to handle reopens. We need it on
>> following qcow2_do_open, to don't try loading bitmaps again. So, we are
>> fixing qcow2_invalidate_cache().
>>
>> However, if we fix only qcow2_invalidate_cache, iotest 169 fails on
>> case test__persistent__not_migbitmap__online_shared, because on first
>> target open, source is not yet closed, and is not yet stored bitmaps,
>> so, we are load nothing. And on second open, dirty_bitmaps_loaded is
>> already true, but we have no bitmaps to reopen with
>> qcow2_reopen_bitmaps_rw_hint(). So, we are fixing qcow2_do_open() too.
>>
>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>> ---
>>  block/qcow2.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/block/qcow2.c b/block/qcow2.c
>> index 6fa5e1d71a..b4216a5830 100644
>> --- a/block/qcow2.c
>> +++ b/block/qcow2.c
>> @@ -1499,7 +1499,7 @@ static int coroutine_fn qcow2_do_open(BlockDriverState *bs, QDict *options,
>>          {
>>              qcow2_reopen_bitmaps_rw_hint(bs, &header_updated, &local_err);
>>          }
>> -    } else {
>> +    } else if (s->nb_bitmaps > 0) {
>>          header_updated = qcow2_load_dirty_bitmaps(bs, &local_err);
>>          s->dirty_bitmaps_loaded = true;
>>      }
>> @@ -2178,6 +2178,7 @@ static void coroutine_fn qcow2_co_invalidate_cache(BlockDriverState *bs,
>>      QDict *options;
>>      Error *local_err = NULL;
>>      int ret;
>> +    bool dirty_bitmaps_loaded = s->dirty_bitmaps_loaded;
>>  
>>      /*
>>       * Backing files are read-only which makes all of their metadata immutable,
>> @@ -2190,6 +2191,7 @@ static void coroutine_fn qcow2_co_invalidate_cache(BlockDriverState *bs,
>>      qcow2_close(bs);
>>  
>>      memset(s, 0, sizeof(BDRVQcow2State));
>> +    s->dirty_bitmaps_loaded = dirty_bitmaps_loaded;
>>      options = qdict_clone_shallow(bs->options);
>>  
>>      flags &= ~BDRV_O_INACTIVE;
>>
> 
> Ah, tch... I didn't realize that invalidate completely wipes the qcow2
> metadata.
> 
> I guess the other three fields, nb_bitmaps, bitmap_directory_size and
> bitmap_directory_offset get initialized again on re-open.
> 
> (I suppose this means I need to rethink caching bm_list more carefully,
> too...)
> 
> I think this looks correct mechanically.
> 

Oh, I meant:

Reviewed-by: John Snow <jsnow@redhat.com>