Re: [PATCH v4 01/31] errp: rename errp to errp_in where it is IN-argument

[Markus Armbruster <armbru@redhat.com>]

Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> writes:

> 08.10.2019 12:08, Markus Armbruster wrote:
>> Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> writes:
>> 
>>> Error **errp is almost always OUT-argument: it's assumed to be NULL, or
>>> pointer to NULL-initialized pointer, or pointer to error_abort or
>>> error_fatal, for callee to report error.
>> 
>> Yes.
>> 
>>> But very few functions instead get Error **errp as IN-argument:
>>> it's assumed to be set, and callee should clean it.
>> 
>> What do you mean by "callee should clean"?  Let's see below.
>> 
>>> In such cases, rename errp to errp_in.
>> 
>> I acknowledge that errp arguments that don't have the usual meaning can
>> be confusing.
>> 
>> Naming can help, comments can help, but perhaps we can tweak the code to
>> avoid the problem instead.  Let's see:
>> 
>>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>>> Reviewed-by: Eric Blake <eblake@redhat.com>
[...]
>> We can avoid the confusing Error **errp in all three cases by peeling
>> off an indirection.  What do you think?
>> 
>
> I like the idea, thanks! I think, I'll try to make a patch.
>
> But you are right, unfortunately there more cases, at least, pointed by
> Greg
>
> error_append_socket_sockfd_hint and
> error_append_security_model_hint
>
> Which don't free error..

Neither do error_append_hint() and error_prepend().

For anything named error_append_FOO_hint() or error_prepend_FOO(),
confusion seems unlikely.

>                          But if they append hint, they should always be called
> on wrapped errp, accordingly to the problem about fatal_error, so they may
> be converted to Error *err too.. Hmm, I should think about the script to find
> such functions.

I figure I better read more of your series before I comment on this
thought.