Re: [Qemu-devel] [PATCH 23/24] qcow2: add .bdrv_remove_persistent_dirty_bitmap

[Max Reitz <mreitz@redhat.com>]

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On 01.02.2017 14:57, Vladimir Sementsov-Ogievskiy wrote:
> 01.02.2017 02:20, Max Reitz wrote:
>> On 23.01.2017 13:10, Vladimir Sementsov-Ogievskiy wrote:
>>> Realize .bdrv_remove_persistent_dirty_bitmap interface.
>>>
>>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>>> ---
>>>   block/qcow2-bitmap.c | 40 ++++++++++++++++++++++++++++++++++++++++
>>>   block/qcow2.c        |  1 +
>>>   block/qcow2.h        |  3 +++
>>>   3 files changed, 44 insertions(+)
>>>
>>> diff --git a/block/qcow2-bitmap.c b/block/qcow2-bitmap.c
>>> index 2687a3acd5..be026fc80e 100644
>>> --- a/block/qcow2-bitmap.c
>>> +++ b/block/qcow2-bitmap.c
>>> @@ -1064,6 +1064,46 @@ static Qcow2Bitmap
>>> *find_bitmap_by_name(Qcow2BitmapList *bm_list,
>>>       return NULL;
>>>   }
>>>   +void qcow2_remove_persistent_dirty_bitmap(BlockDriverState *bs,
>>> +                                          const char *name,
>>> +                                          Error **errp)
>>> +{
>>> +    int ret;
>>> +    BDRVQcow2State *s = bs->opaque;
>>> +    Qcow2Bitmap *bm;
>>> +    Qcow2BitmapList *bm_list;
>>> +
>>> +    if (s->nb_bitmaps == 0) {
>>> +        /* No bitmaps - nothing to do */
>> Shouldn't it be an error? I.e. "bitmap not found"?
>>
>>> +        return;
>>> +    }
>>> +
>>> +    bm_list = bitmap_list_load(bs, s->bitmap_directory_offset,
>>> +                               s->bitmap_directory_size, errp);
>>> +    if (bm_list == NULL) {
>>> +        return;
>>> +    }
>>> +
>>> +    bm = find_bitmap_by_name(bm_list, name);
>>> +    if (bm == NULL) {
>>> +        goto fail;
>> What about setting errp? Or do you not consider this an error?
>>
>> I think it should be an error.
> 
> Hmm. The following scenery should not be an error:
> 1. qmp create dirty bitmap with persistent = true (bitmap not exists and
> not created  in the storage, it will be saved only on storage close)
> 2. qmp remove dirty bitmap. persistent = true, so we will try to remove
> it from storage..

That's a good point.

> So, I see following variants:
> 1. as is, just add comment "remove if exists"
> 2. add return value to this function, return ENOENT if bitmap not found
> and ignore this ENOENT in qmp_remove_bitmap
> 3. add additional bool field 'exist_in_storage' to BdrvDirtyBitmap.

1 sounds the best to me. I don't think there is a reason why a bitmap
may not be found other than the scenario you've described.

It would be good if the comment included that explanation as for why
it's not an error.

Max


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