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 F0D6EC83F25 for ; Mon, 21 Jul 2025 13:35:20 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1udqar-0001tU-N1; Mon, 21 Jul 2025 09:30:14 -0400 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 1udqaV-0001AP-UA for qemu-devel@nongnu.org; Mon, 21 Jul 2025 09:29:51 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1udqaS-0005l9-NV for qemu-devel@nongnu.org; Mon, 21 Jul 2025 09:29:51 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1753104585; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:in-reply-to:in-reply-to: references:references; bh=QsubmAraLDXUmpWBhBcD/QEzJQUuw7w765c5grJH+SU=; b=dXT+4wX02R1Ddvxxu9vmmdFS9oLtY1ZSZ5iWvI80VJg6RlK91ymDpJX9QqdV4sXyrpOYEd KIsI495Jh5AR+MHGCFpKDCs9eEMxNeSH+cACQfBo/y40HluJ1kqvYrEullq1yRjxkOs4/S ZqbT9i7Y+25iOk2kcJy5Pa+GCOVTWkU= Received: from mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-303-AvLfv6biMcWs46Sr7ULRgg-1; Mon, 21 Jul 2025 09:29:42 -0400 X-MC-Unique: AvLfv6biMcWs46Sr7ULRgg-1 X-Mimecast-MFC-AGG-ID: AvLfv6biMcWs46Sr7ULRgg_1753104580 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (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-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id CE2071956048; Mon, 21 Jul 2025 13:29:38 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.213]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id ED8E51800D82; Mon, 21 Jul 2025 13:29:28 +0000 (UTC) Date: Mon, 21 Jul 2025 14:29:25 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Akihiko Odaki Cc: Arun Menon , qemu-devel@nongnu.org, "Michael S. Tsirkin" , Marcel Apfelbaum , Cornelia Huck , Halil Pasic , Eric Farman , Richard Henderson , David Hildenbrand , Ilya Leoshkevich , Thomas Huth , Christian Borntraeger , Paolo Bonzini , Fam Zheng , Nicholas Piggin , Daniel Henrique Barboza , Harsh Prateek Bora , Alex Williamson , =?utf-8?Q?C=C3=A9dric?= Le Goater , Peter Xu , Fabiano Rosas , Hailiang Zhang , Steve Sistare , qemu-s390x@nongnu.org, qemu-ppc@nongnu.org, Stefan Berger , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , Alex =?utf-8?Q?Benn=C3=A9e?= , Dmitry Osipenko , Matthew Rosato Subject: Re: [PATCH v6 23/24] migration: Add error-parameterized function variants in VMSD struct Message-ID: References: <20250721-propagate_tpm_error-v6-0-fef740e15e17@redhat.com> <20250721-propagate_tpm_error-v6-23-fef740e15e17@redhat.com> <3e9aa703-2805-4ac4-9f10-f4ba71c10c8a@rsg.ci.i.u-tokyo.ac.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <3e9aa703-2805-4ac4-9f10-f4ba71c10c8a@rsg.ci.i.u-tokyo.ac.jp> User-Agent: Mutt/2.2.14 (2025-02-20) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.926, 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_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Mon, Jul 21, 2025 at 10:14:30PM +0900, Akihiko Odaki wrote: > On 2025/07/21 20:29, Arun Menon wrote: > > - We need to have good error reporting in the callbacks in > > VMStateDescription struct. Specifically pre_save, post_save, > > pre_load and post_load callbacks. > > - It is not possible to change these functions everywhere in one > > patch, therefore, we introduce a duplicate set of callbacks > > with Error object passed to them. > > - So, in this commit, we implement 'errp' variants of these callbacks, > > introducing an explicit Error object parameter. > > - This is a functional step towards transitioning the entire codebase > > to the new error-parameterized functions. > > - Deliberately called in mutual exclusion from their counterparts, > > to prevent conflicts during the transition. > > - New impls should preferentally use 'errp' variants of > > these methods, and existing impls incrementally converted. > > The variants without 'errp' are intended to be removed > > once all usage is converted. > > > > Signed-off-by: Arun Menon > > --- > > include/migration/vmstate.h | 11 +++++++++++ > > migration/vmstate.c | 47 +++++++++++++++++++++++++++++++++++++++------ > > 2 files changed, 52 insertions(+), 6 deletions(-) > > > > diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h > > index 056781b1c21e737583f081594d9f88b32adfd674..53fa72c1bbde399be02c88fc8745fdbb79bfd7c8 100644 > > --- a/include/migration/vmstate.h > > +++ b/include/migration/vmstate.h > > @@ -200,15 +200,26 @@ struct VMStateDescription { > > * exclusive. For this reason, also early_setup VMSDs are migrated in a > > * QEMU_VM_SECTION_FULL section, while save_setup() data is migrated in > > * a QEMU_VM_SECTION_START section. > > + * > > + * There are duplicate impls of the post/pre save/load hooks. > > + * New impls should preferentally use 'errp' variants of these > > + * methods and existing impls incrementally converted. > > + * The variants without 'errp' are intended to be removed > > + * once all usage is converted. > > */ > > + > > bool early_setup; > > int version_id; > > int minimum_version_id; > > MigrationPriority priority; > > int (*pre_load)(void *opaque); > > + int (*pre_load_errp)(void *opaque, Error **errp); > > int (*post_load)(void *opaque, int version_id); > > + int (*post_load_errp)(void *opaque, int version_id, Error **errp); > > int (*pre_save)(void *opaque); > > + int (*pre_save_errp)(void *opaque, Error **errp); > > int (*post_save)(void *opaque); > > + int (*post_save_errp)(void *opaque, Error **errp); > > I think the new functions should have void as return value instead. > > As I discussed before, I think having an integer return value is a source of > confusion: > https://lore.kernel.org/qemu-devel/0447e269-c242-4cd7-b68e-d0c7211784a7@rsg.ci.i.u-tokyo.ac.jp/ > > In the previous discussion, I suggested using bool, but void fits better in > this particular case. > > include/qapi/error.h says: > > Whenever practical, also return a value that indicates success / > > failure. This can make the error checking more concise, and can avoid > > useless error object creation and destruction. Note that we still > > have many functions returning void. > > There will be more implementations of these function pointers than their > callers, so it makes more sense to let return void and make implementations > more concise while making the callers less so. There is also DeviceRealize, > an example of function pointer type that takes errp but returns void. No, please do NOT make these functions void. As that text you quote says, we want functions to return a value indicating success/failure. 'void' return is a historical practice we don't want to continue in QEMU. Given that the existing methods all return 'int', we should remain consistent with the new functions and return 'int', with -1 for failure, 0 for success, and not use bool. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|