From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_2 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E82B8C32771 for ; Wed, 15 Jan 2020 18:34:35 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id BCA34214AF for ; Wed, 15 Jan 2020 18:34:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BCA34214AF Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kaod.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:58728 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1irnUw-0001Kg-R0 for qemu-devel@archiver.kernel.org; Wed, 15 Jan 2020 13:34:34 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:55812) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1irnU6-0000UF-0C for qemu-devel@nongnu.org; Wed, 15 Jan 2020 13:33:43 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1irnU3-0004hB-DO for qemu-devel@nongnu.org; Wed, 15 Jan 2020 13:33:41 -0500 Received: from 1.mo4.mail-out.ovh.net ([178.33.248.196]:35545) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1irnU3-0004gB-66 for qemu-devel@nongnu.org; Wed, 15 Jan 2020 13:33:39 -0500 Received: from player772.ha.ovh.net (unknown [10.108.1.219]) by mo4.mail-out.ovh.net (Postfix) with ESMTP id DC15A21F96F for ; Wed, 15 Jan 2020 19:33:36 +0100 (CET) Received: from kaod.org (lns-bzn-46-82-253-208-248.adsl.proxad.net [82.253.208.248]) (Authenticated sender: groug@kaod.org) by player772.ha.ovh.net (Postfix) with ESMTPSA id 53518E51772A; Wed, 15 Jan 2020 18:33:14 +0000 (UTC) Date: Wed, 15 Jan 2020 19:33:12 +0100 From: Greg Kurz To: Vladimir Sementsov-Ogievskiy Subject: Re: [PATCH v6 02/11] error: auto propagated local_err Message-ID: <20200115193312.60e965ec@bahia.lan> In-Reply-To: <20200110194158.14190-3-vsementsov@virtuozzo.com> References: <20200110194158.14190-1-vsementsov@virtuozzo.com> <20200110194158.14190-3-vsementsov@virtuozzo.com> X-Mailer: Claws Mail 3.17.4 (GTK+ 2.24.32; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Ovh-Tracer-Id: 6557241061147122003 X-VR-SPAMSTATE: OK X-VR-SPAMSCORE: -100 X-VR-SPAMCAUSE: gggruggvucftvghtrhhoucdtuddrgedugedrtdefgdduudefucetufdoteggodetrfdotffvucfrrhhofhhilhgvmecuqfggjfdpvefjgfevmfevgfenuceurghilhhouhhtmecuhedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmnecujfgurhepfffhvffukfgjfhfogggtgfesthhqredtredtjeenucfhrhhomhepifhrvghgucfmuhhriicuoehgrhhouhhgsehkrghougdrohhrgheqnecukfhppedtrddtrddtrddtpdekvddrvdehfedrvddtkedrvdegkeenucfrrghrrghmpehmohguvgepshhmthhpqdhouhhtpdhhvghlohepphhlrgihvghrjeejvddrhhgrrdhovhhhrdhnvghtpdhinhgvtheptddrtddrtddrtddpmhgrihhlfhhrohhmpehgrhhouhhgsehkrghougdrohhrghdprhgtphhtthhopehqvghmuhdquggvvhgvlhesnhhonhhgnhhurdhorhhgnecuvehluhhsthgvrhfuihiivgeptd X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 178.33.248.196 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Stefano Stabellini , Laszlo Ersek , qemu-block@nongnu.org, Paul Durrant , Philippe =?UTF-8?B?TWF0aGlldS1EYXVkw6k=?= , Cornelia Huck , qemu-devel@nongnu.org, Max Reitz , Gerd Hoffmann , Stefan Hajnoczi , Anthony Perard , xen-devel@lists.xenproject.org, Michael Roth , Markus Armbruster , Stefan Berger Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, 10 Jan 2020 22:41:49 +0300 Vladimir Sementsov-Ogievskiy wrote: > Here is introduced ERRP_AUTO_PROPAGATE macro, to be used at start of > functions with errp OUT parameter. >=20 > It has three goals: >=20 > 1. Fix issue with error_fatal & error_prepend/error_append_hint: user > can't see this additional information, because exit() happens in > error_setg earlier than information is added. [Reported by Greg Kurz] >=20 > 2. Fix issue with error_abort & error_propagate: when we wrap > error_abort by local_err+error_propagate, resulting coredump will > refer to error_propagate and not to the place where error happened. > (the macro itself doesn't fix the issue, but it allows to [3.] drop all > local_err+error_propagate pattern, which will definitely fix the issue) > [Reported by Kevin Wolf] >=20 > 3. Drop local_err+error_propagate pattern, which is used to workaround > void functions with errp parameter, when caller wants to know resulting > status. (Note: actually these functions could be merely updated to > return int error code). >=20 > To achieve these goals, we need to add invocation of the macro at start > of functions, which needs error_prepend/error_append_hint (1.); add > invocation of the macro at start of functions which do > local_err+error_propagate scenario the check errors, drop local errors > from them and just use *errp instead (2., 3.). >=20 > Signed-off-by: Vladimir Sementsov-Ogievskiy > --- >=20 LGTM Reviewed-by: Greg Kurz > CC: Cornelia Huck > CC: Eric Blake > CC: Kevin Wolf > CC: Max Reitz > CC: Greg Kurz > CC: Stefan Hajnoczi > CC: Stefano Stabellini > CC: Anthony Perard > CC: Paul Durrant > CC: "Philippe Mathieu-Daud=C3=A9" > CC: Laszlo Ersek > CC: Gerd Hoffmann > CC: Stefan Berger > CC: Markus Armbruster > CC: Michael Roth > CC: qemu-block@nongnu.org > CC: xen-devel@lists.xenproject.org >=20 > include/qapi/error.h | 84 +++++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 83 insertions(+), 1 deletion(-) >=20 > diff --git a/include/qapi/error.h b/include/qapi/error.h > index fa8d51fd6d..532b9afb9e 100644 > --- a/include/qapi/error.h > +++ b/include/qapi/error.h > @@ -78,7 +78,7 @@ > * Call a function treating errors as fatal: > * foo(arg, &error_fatal); > * > - * Receive an error and pass it on to the caller: > + * Receive an error and pass it on to the caller (DEPRECATED*): > * Error *err =3D NULL; > * foo(arg, &err); > * if (err) { > @@ -98,6 +98,50 @@ > * foo(arg, errp); > * for readability. > * > + * DEPRECATED* This pattern is deprecated now, use ERRP_AUTO_PROPAGATE m= acro > + * instead (defined below). > + * It's deprecated because of two things: > + * > + * 1. Issue with error_abort & error_propagate: when we wrap error_abort= by > + * local_err+error_propagate, resulting coredump will refer to error_pro= pagate > + * and not to the place where error happened. > + * > + * 2. A lot of extra code of the same pattern > + * > + * How to update old code to use ERRP_AUTO_PROPAGATE? > + * > + * All you need is to add ERRP_AUTO_PROPAGATE() invocation at function s= tart, > + * than you may safely dereference errp to check errors and do not need = any > + * additional local Error variables or calls to error_propagate(). > + * > + * Example: > + * > + * old code > + * > + * void fn(..., Error **errp) { > + * Error *err =3D NULL; > + * foo(arg, &err); > + * if (err) { > + * handle the error... > + * error_propagate(errp, err); > + * return; > + * } > + * ... > + * } > + * > + * updated code > + * > + * void fn(..., Error **errp) { > + * ERRP_AUTO_PROPAGATE(); > + * foo(arg, errp); > + * if (*errp) { > + * handle the error... > + * return; > + * } > + * ... > + * } > + * > + * > * Receive and accumulate multiple errors (first one wins): > * Error *err =3D NULL, *local_err =3D NULL; > * foo(arg, &err); > @@ -348,6 +392,44 @@ void error_set_internal(Error **errp, > ErrorClass err_class, const char *fmt, ...) > GCC_FMT_ATTR(6, 7); > =20 > +typedef struct ErrorPropagator { > + Error *local_err; > + Error **errp; > +} ErrorPropagator; > + > +static inline void error_propagator_cleanup(ErrorPropagator *prop) > +{ > + error_propagate(prop->errp, prop->local_err); > +} > + > +G_DEFINE_AUTO_CLEANUP_CLEAR_FUNC(ErrorPropagator, error_propagator_clean= up); > + > +/* > + * ERRP_AUTO_PROPAGATE > + * > + * This macro is created to be the first line of a function which use > + * Error **errp parameter to report error. It's needed only in cases whe= re we > + * want to use error_prepend, error_append_hint or dereference *errp. It= 's > + * still safe (but useless) in other cases. > + * > + * If errp is NULL or points to error_fatal, it is rewritten to point to= a > + * local Error object, which will be automatically propagated to the ori= ginal > + * errp on function exit (see error_propagator_cleanup). > + * > + * After invocation of this macro it is always safe to dereference errp > + * (as it's not NULL anymore) and to add information (by error_prepend or > + * error_append_hint) > + * (as, if it was error_fatal, we swapped it with a local_error to be > + * propagated on cleanup). > + * > + * Note: we don't wrap the error_abort case, as we want resulting coredu= mp > + * to point to the place where the error happened, not to error_propagat= e. > + */ > +#define ERRP_AUTO_PROPAGATE() \ > + g_auto(ErrorPropagator) _auto_errp_prop =3D {.errp =3D errp}; \ > + errp =3D ((errp =3D=3D NULL || *errp =3D=3D error_fatal) = \ > + ? &_auto_errp_prop.local_err : errp) > + > /* > * Special error destination to abort on error. > * See error_setg() and error_propagate() for details.