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

From: Markus Armbruster
Subject: Re: [PATCH v4 for-5.2 1/2] spapr: Use error_append_hint() in spapr_caps.c
Date: Mon, 20 Jul 2020 17:24:35 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux)

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

 * = 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.

No need to make an argument involving the possible arguments (pardon the


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