Re: [PATCH v4 for-5.2 1/2] spapr: Use error_append_hint() in spapr_caps.c

[Greg Kurz <groug@kaod.org>]

On Mon, 20 Jul 2020 17:24:35 +0200
Markus Armbruster <armbru@redhat.com> wrote:

> Greg Kurz <groug@kaod.org> writes:
> 
> > We have a dedicated error API for hints. Use it instead of embedding
> > the hint in the error message, as recommanded in the "qapi/error.h"
> > header file.
> >
> > Since spapr_caps_apply() passes &error_fatal, all functions must
> > also call the ERRP_GUARD() macro for error_append_hint() to be
> > functional.
> 
> This isn't a request for change in this patch, just an attempt to squash
> possible misunderstandings.
> 
> It's true that error_append_hint() without ERRP_GUARD() works as long as
> the caller doesn't pass certain errp arguments.  But the callee should
> work for all possible @errp arguments, not just the ones that get passed
> today.  That's why error.h wants you to guard *all* uses of
> error_append_hint(errp):
> 
>  * = Why, when and how to use ERRP_GUARD() =
>  *
>  * Without ERRP_GUARD(), use of the @errp parameter is restricted:
>  * - It must not be dereferenced, because it may be null.
>  * - It should not be passed to error_prepend() or
>  *   error_append_hint(), because that doesn't work with &error_fatal.
>  * ERRP_GUARD() lifts these restrictions.
> 

Yeah, I just wanted to emphasize that we were precisely in the case
where we _really_ need to lift the restriction, but I'm perfectly fine
with dropping this sentence if you consider it useless.

BTW, should we have a way for CI to ensure that a patch that adds
error_prepend(errp, ...) or error_append_hint(errp, ...) also adds
ERRP_GUARD() ? Not sure that people read error.h that often...

> No need to make an argument involving the possible arguments (pardon the
> pun).
> 

:)

> [...]
>