Re: [Qemu-block] [PATCH v2 2/6] block/dirty-bitmaps: rename frozen predicate helper

[John Snow]

On 2/18/19 8:57 AM, Vladimir Sementsov-Ogievskiy wrote:
> 14.02.2019 2:23, John Snow wrote:
>> "Frozen" was a good description a long time ago, but it isn't adequate now.
>> Rename the frozen predicate to has_successor to make the semantics of the
>> predicate more clear to outside callers.
>>
>> In the process, remove some calls to frozen() that no longer semantically
>> make sense. For enabled and disabled in particular, it's actually okay for
>> the internals to do this but only forbidden for users to invoke them, and
> 
> I'm a bit lost in this paragraph.. to this - what?, to invoke them - whom?
> I think, it would be simpler for me to read patch itself :)
> 

Touched this up. I meant enable and disable, not enabled and disabled.

>> all of the QMP entry uses already check against qmp_locked.
>>
>> Several other assertions really want to check that the bitmap isn't in-use
>> by another operation -- use the qmp_locked function for this instead, which
>> presently also checks for has_successor.
> 
> hm, you mean user_locked, not qmp_locked.
> 

Yes.

[...]

>>   /**
>>    * Create a successor bitmap destined to replace this bitmap after an 
>> operation.
>> - * Requires that the bitmap is not frozen and has no successor.
>> + * Requires that the bitmap is not locked and has no successor.
> 
> I think, user_locked, to not interfere with bitmaps mutex. And you use 
> user_locked in
> other comments in this patch.
> 

You're right. It gets changed again later, but I didn't make this easy
to read.

>>    * Called with BQL taken.
>>    */
>>   int bdrv_dirty_bitmap_create_successor(BlockDriverState *bs,
>> @@ -244,12 +244,16 @@ int 
>> bdrv_dirty_bitmap_create_successor(BlockDriverState *bs,
>>       uint64_t granularity;
>>       BdrvDirtyBitmap *child;
>>   
>> -    if (bdrv_dirty_bitmap_frozen(bitmap)) {
>> -        error_setg(errp, "Cannot create a successor for a bitmap that is "
>> -                   "currently frozen");
>> +    if (bdrv_dirty_bitmap_user_locked(bitmap)) {
>> +        error_setg(errp, "Cannot create a successor for a bitmap that is 
>> in-use "
>> +                   "by an operation");
>> +        return -1;
>> +    }
>> +    if (bdrv_dirty_bitmap_has_successor(bitmap)) {
>> +        error_setg(errp, "Cannot create a successor for a bitmap that 
>> already "
>> +                   "has one");
> 
> 
> Amm, dead code? _user_locked() implies no successor, so we instead can keep 
> an assertion..
> 

It gets changed later in the series, but I didn't do a great job of
explaining that in advance. I'll amend the commit message to explain
what I'm trying to do.

I tried to hint at this with: "which presently also checks for
has_successor" as an admission that it was redundant, but I need to call
it out in stronger language.