Re: [Qemu-block] [Qemu-devel] [PATCH 3/6] bloc/qcow2: drop dirty_bitmaps_loaded state variable

[John Snow]

On 07/10/2018 03:43 AM, Vladimir Sementsov-Ogievskiy wrote:
> 10.07.2018 02:25, John Snow wrote:
>>
>> On 06/26/2018 09:50 AM, Vladimir Sementsov-Ogievskiy wrote:
>>> This variable doesn't work as it should, because it is actually cleared
>>> in qcow2_co_invalidate_cache() by memset(). Drop it, as the following
>>> patch will introduce new behavior.
>>>
>>> Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
>>> ---
>>>   block/qcow2.h |  1 -
>>>   block/qcow2.c | 19 ++-----------------
>>>   2 files changed, 2 insertions(+), 18 deletions(-)
>>>
>>> diff --git a/block/qcow2.h b/block/qcow2.h
>>> index 01b5250415..c9df19b6e6 100644
>>> --- a/block/qcow2.h
>>> +++ b/block/qcow2.h
>>> @@ -294,7 +294,6 @@ typedef struct BDRVQcow2State {
>>>       uint32_t nb_bitmaps;
>>>       uint64_t bitmap_directory_size;
>>>       uint64_t bitmap_directory_offset;
>>> -    bool dirty_bitmaps_loaded;
>>>         int flags;
>>>       int qcow_version;
>>> diff --git a/block/qcow2.c b/block/qcow2.c
>>> index 46194a33ca..0044ff58e7 100644
>>> --- a/block/qcow2.c
>>> +++ b/block/qcow2.c
>>> @@ -1149,7 +1149,6 @@ static int coroutine_fn
>>> qcow2_do_open(BlockDriverState *bs, QDict *options,
>>>       uint64_t ext_end;
>>>       uint64_t l1_vm_state_index;
>>>       bool update_header = false;
>>> -    bool header_updated = false;
>>>         ret = bdrv_pread(bs->file, 0, &header, sizeof(header));
>>>       if (ret < 0) {
>>> @@ -1488,23 +1487,9 @@ static int coroutine_fn
>>> qcow2_do_open(BlockDriverState *bs, QDict *options,
>>>           s->autoclear_features &= QCOW2_AUTOCLEAR_MASK;
>>>       }
>>>   -    if (s->dirty_bitmaps_loaded) {
>>> -        /* It's some kind of reopen. There are no known cases where
>>> we need to
>>> -         * reload bitmaps in such a situation, so it's safer to skip
>>> them.
>>> -         *
>>> -         * Moreover, if we have some readonly bitmaps and we are
>>> reopening for
>>> -         * rw we should reopen bitmaps correspondingly.
>>> -         */
>>> -        if (bdrv_has_readonly_bitmaps(bs) &&
>>> -            !bdrv_is_read_only(bs) && !(bdrv_get_flags(bs) &
>>> BDRV_O_INACTIVE))
>>> -        {
>>> -            qcow2_reopen_bitmaps_rw_hint(bs, &header_updated,
>>> &local_err);
>>> -        }
>>> -    } else {
>>> -        header_updated = qcow2_load_dirty_bitmaps(bs, &local_err);
>>> -        s->dirty_bitmaps_loaded = true;
>>> +    if (qcow2_load_dirty_bitmaps(bs, &local_err)) {
>>> +        update_header = false;
>>>       }
>>> -    update_header = update_header && !header_updated;
>>>       if (local_err != NULL) {
>>>           error_propagate(errp, local_err);
>>>           ret = -EINVAL;
>>>
>> Usually I'd like to see the new behavior introduced before removing the
>> old, imperfect solution... (it doesn't make any tests fail!? ...)
>>
>> At this point in the series I just have to trust that you will fix it to
>> be better :)
> 
> As I understand, this field is actually always false, so it's safe to
> drop it.

Ah, you know, I think I was remembering a patch (?) where you explicitly
cache this value and restore it -- but that must have been a previous
incarnation of this patchset.

I realize now that as the code actually exists in origin/master that
it's always going to be false, yeah.

--js