Re: [Qemu-devel] [PATCH] dirty-bitmap: remove unnecessary return

[Changlong Xie <xiecl.fnst@cn.fujitsu.com>]

On 07/01/2016 02:18 AM, John Snow wrote:
>
>
> On 06/30/2016 10:00 AM, Jeff Cody wrote:
>> On Thu, Jun 30, 2016 at 04:45:52PM +0800, Changlong Xie wrote:
>>> On 06/30/2016 04:25 PM, Fam Zheng wrote:
>>>> On Thu, 06/30 16:01, Changlong Xie wrote:
>>>>> Otherwise, we could never trigger assert(!bitmap->successor)
>>>>>
>>>>> Signed-off-by: Changlong Xie <xiecl.fnst@cn.fujitsu.com>
>>>>> ---
>>>>>   block/dirty-bitmap.c | 1 -
>>>>>   1 file changed, 1 deletion(-)
>>>>>
>>>>> diff --git a/block/dirty-bitmap.c b/block/dirty-bitmap.c
>>>>> index 4902ca5..e9df5ac 100644
>>>>> --- a/block/dirty-bitmap.c
>>>>> +++ b/block/dirty-bitmap.c
>>>>> @@ -131,7 +131,6 @@ int bdrv_dirty_bitmap_create_successor(BlockDriverState *bs,
>>>>>       if (bdrv_dirty_bitmap_frozen(bitmap)) {
>>>>>           error_setg(errp, "Cannot create a successor for a bitmap that is "
>>>>>                      "currently frozen");
>>>>> -        return -1;
>>>>>       }
>>>>>       assert(!bitmap->successor);
>>>>
>>>> This is wrong. Then we will always trigger assert for a frozen bitmap.
>>>>
>>>
>>> IMO, when it's a frozen bitmap, we will always return -1. So
>>> "assert(!bitmap->successor)" is useless here, am i right?
>>>
>>
>> I don't see a path where the assert could trigger, so I would agree that the
>> assert itself, while harmless, is not necessary (although it could be argued
>> it is in place in case the code above it changes in a way that does not
>> check bitmap->successor).

Agree

>>
>> That doesn't mean we want to try and trigger an assert, however! :) The
>> error return is the proper error handling -- we don't expect that asserts
>> should ever be encountered QEMU, if one happens that is a sign of a bug.
>>

Got it

>> Jeff
>>
>
> The assert was indeed added to ensure that if the valid states of the
> bitmap later expanded or changed, that the status checkers (e.g.
> bdrv_dirty_bitmap_frozen()) were changed to match.
>

Thanks for all explanations. Although my brain always forces to think 
it's a redundant execution path, but since it's harmless, let's keep it.

>
> .
>