Re: [PATCH v6 23/24] migration: Add error-parameterized function variants in VMSD struct

[Markus Armbruster <armbru@redhat.com>]

Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp> writes:

> On 2025/08/09 17:17, Markus Armbruster wrote:
>> Almost missed this, sorry.
>> Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp> writes:
>> 
>>> On 2025/07/21 22:29, Daniel P. Berrangé wrote:

[...]

>>>> No, please do NOT make these functions void. As that text you quote
>>>> says, we want functions to return a value indicating success/failure.
>>>> 'void' return is a historical practice we don't want to continue
>>>> in QEMU.
>>>>
>>>> Given that the existing methods all return 'int', we should remain
>>>> consistent with the new functions and return 'int', with -1 for
>>>> failure, 0 for success, and not use bool.
>>>
>>> Markus, I'd also like to hear your opinion since you are the maintainer of the error reporting facility.
>>
>> I'm with Daniel.
>>
>> New code should stick to the rules.
>>
>> Changing existing code from "sticks to the rules" to not requires pretty
>> compelling justification.
>>
>> The other direction is more welcome, but whether the juice is worth the
>> squeeze still needs to be decided case by case.
>
> What do you refer with the rules?

The big comment in qapi/error.h starts with a section = Rules =.

> There were three options on the table: bool, int, and void.
>
> The previous discussion you referred explains why void should be avoided, and include/qapi/error.h also says void should be avoided.
>
> There is pre_load() that does not use Error returns int, but now we are adding pre_load_errp() that uses Error.
>
> Then what pre_load_errp() should return: bool or int?

I like bool when it's all we need.

When we need to return a non-negative int on success, use int and return
-1 or a negative error code on failure.

Another reason to pick int is local consistency: related functions
already use int.

Changing working code from int to bool doesn't seem worth the bother.

Questions?