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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 137A8D0E6C4 for ; Tue, 25 Nov 2025 11:46:34 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1vNrUu-00022i-JH; Tue, 25 Nov 2025 06:46:16 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1vNrUs-00020g-89 for qemu-devel@nongnu.org; Tue, 25 Nov 2025 06:46:14 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1vNrUq-0008SU-2q for qemu-devel@nongnu.org; Tue, 25 Nov 2025 06:46:13 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1764071168; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=GQpjXUgBwbRc8kvJ0Wf1OVgFFD0DeTcUjFsYZBuUQxY=; b=X1y2kFxON1aNw9ApgB5foJRyMzQlwZLdC8yQiLIiOlAmGKmSZWKLG+TS3GoseQyT6gLJGp 9lhACLtm2216AoNaMwzuTb5I2uA17/G8oJCAnrsz1HDH8G9/3dfRRP8u6ICg9LHtR/QOIx iwYZEYJpCAfZpNhHNJDU6QWspnGOnjQ= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-680-HPMZR-tkNIWC3uKtiPB5lg-1; Tue, 25 Nov 2025 06:46:05 -0500 X-MC-Unique: HPMZR-tkNIWC3uKtiPB5lg-1 X-Mimecast-MFC-AGG-ID: HPMZR-tkNIWC3uKtiPB5lg_1764071164 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 1AC901800372; Tue, 25 Nov 2025 11:46:04 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.45.242.3]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 8BD6F3003E40; Tue, 25 Nov 2025 11:46:03 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 26EF221E6A27; Tue, 25 Nov 2025 12:46:01 +0100 (CET) From: Markus Armbruster To: Daniel P. =?utf-8?Q?Berrang=C3=A9?= Cc: qemu-devel@nongnu.org, peterx@redhat.com, farosas@suse.de, peter.maydell@linaro.org Subject: Re: g_autoptr(Error) In-Reply-To: ("Daniel P. =?utf-8?Q?Berrang?= =?utf-8?Q?=C3=A9=22's?= message of "Tue, 25 Nov 2025 11:25:32 +0000") References: <20251125070554.2256181-1-armbru@redhat.com> <871plmk1bc.fsf@pond.sub.org> Date: Tue, 25 Nov 2025 12:46:01 +0100 Message-ID: <87jyzexrly.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.075, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Daniel P. Berrang=C3=A9 writes: > On Tue, Nov 25, 2025 at 08:40:07AM +0100, Markus Armbruster wrote: >> g_autoptr(T) is quite useful when the object's extent matches the >> function's. >>=20 >> This isn't the case for an Error object the function propagates to its >> caller. It is the case for an Error object the function reports or >> handles itself. However, the functions to report Error also free it. >>=20 >> Thus, g_autoptr(Error) is rarely applicable. We have just three >> instances out of >1100 local Error variables, all in migration code. >>=20 >> Two want to move the error to the MigrationState for later handling / >> reporting. Since migrate_set_error() doesn't move, but stores a copy, >> the original needs to be freed, and g_autoptr() is correct there. We >> have 17 more that instead manually free with error_free() or >> error_report_err() right after migrate_set_error(). >>=20 >> We recently discussed storing a copy vs. move the original: >>=20 >> From: Peter Xu >> Subject: Re: [PATCH 0/3] migration: Error fixes and improvements >> Date: Mon, 17 Nov 2025 11:03:37 -0500 >> Message-ID: >>=20 >> The two g_autoptr() gave me pause when I investigated this topic, simply >> because they deviate from the common pattern migrate_set_error(s, err) >> followed by error_free() or error_report_err(). >>=20 >> The third one became wrong when I cleaned up the reporting (missed in >> the cleanup patch, fixed in the patch I'm replying to). I suspect my >> mistake escaped review for the same reason I made it: g_autoptr(Error) >> is unusual and not visible in the patch hunk. >>=20 >> Would you like me to replace the two correct uses of g_autoptr(Error) by >> more common usage? > > I had previously proposed g_autoptr(Error) a year or two back and you > rejected it then, so I'm surprised to see that it got into the code, > because it requires explicit opt-in via a G_DEFINE_AUTOPTR_CLEANUP_FUNC. > > Unfortunately it appears exactly that was added earlier this year in > > commit 18eb55546a54e443d94a4c49286348176ad4b00a > Author: Maciej S. Szmigiero > Date: Tue Mar 4 23:03:35 2025 +0100 > > error: define g_autoptr() cleanup function for the Error type >=20=20=20=20=20 > Automatic memory management helps avoid memory safety issues. >=20=20=20=20=20 > Reviewed-by: Peter Xu > Signed-off-by: Maciej S. Szmigiero > Link: https://lore.kernel.org/qemu-devel/a5843c5fa64d7e5239a4316092ec= 0ef0d10c2320.1741124640.git.maciej.szmigiero@oracle.com > Signed-off-by: C=C3=A9dric Le Goater I missed it. Not he submitter's fault; it was cc'ed to me. > When removing this usage, ensure that commit is reverted too, which > will prevent anyone unwittingly re-introducing g_autoptr(Error) > usage Thanks for the pointer!