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 060BFCCD193 for ; Mon, 20 Oct 2025 11:41:08 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1vAoFu-0006Ni-Dk; Mon, 20 Oct 2025 07:40:50 -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 1vAoFo-0006MQ-DB for qemu-devel@nongnu.org; Mon, 20 Oct 2025 07:40:44 -0400 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 1vAoFk-0001gy-G5 for qemu-devel@nongnu.org; Mon, 20 Oct 2025 07:40:44 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1760960437; 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=fzIxZ0oUmw3zhinDxWb7sXqppuCZIGPUhmoaXMVWQ/E=; b=h/GkQ/Y6vhNmtqvGzaN4JDR4wLVEI3JvqxzEZAM+8POJhCU7FI4ytMJbeR44MnEEeWZQoE 7lYjBNCF8m5EUdnrL7BXMtp3+8mXamlHVSv9cBmBfAPWAr1bjtSxEWLpI/B03s8zGfhFVb 0k3M1vxYyLVmIMGG8o0itcBDbebajiw= Received: from mx-prod-mc-03.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-96-C2CLmfV-PtuUpUDuIPP1Pg-1; Mon, 20 Oct 2025 07:40:34 -0400 X-MC-Unique: C2CLmfV-PtuUpUDuIPP1Pg-1 X-Mimecast-MFC-AGG-ID: C2CLmfV-PtuUpUDuIPP1Pg_1760960432 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-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 973E51956050; Mon, 20 Oct 2025 11:40:32 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.161]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 94A7D30001BC; Mon, 20 Oct 2025 11:40:30 +0000 (UTC) Date: Mon, 20 Oct 2025 12:40:27 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Vladimir Sementsov-Ogievskiy Cc: Markus Armbruster , peterx@redhat.com, stefanb@linux.vnet.ibm.com, farosas@suse.de, qemu-devel@nongnu.org Subject: Re: [PATCH] migration: vmsd errp handlers: return bool Message-ID: References: <20251020091907.2173711-1-vsementsov@yandex-team.ru> <87347d7s0j.fsf@pond.sub.org> <0ce2f913-36c2-44a2-8141-256ff847529d@yandex-team.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <0ce2f913-36c2-44a2-8141-256ff847529d@yandex-team.ru> User-Agent: Mutt/2.2.14 (2025-02-20) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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: , 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, Oct 20, 2025 at 02:22:22PM +0300, Vladimir Sementsov-Ogievskiy wrote: > On 20.10.25 14:05, Markus Armbruster wrote: > > Vladimir Sementsov-Ogievskiy writes: > > > > > Recently we moved to returning errp. Why to keep int return value? > > > Generally it doesn't help: you can't use in a logic of handling > > > an error, as you are never sure, that in future the logic in > > > the stack will not change: it may start to return another error > > > code in the same case, or return same error code in another case. > > > > > > Actually, we can only rely on concrete errno code when get it > > > _directly_ from documented library function or syscall. This way we > > > handle for example EINTR. But later in a stack, we can only add > > > this errno to the textual error by strerror(). > > > > It's a matter of the function's contract, actually. > > > > If the contract is "Return negative value on failure", checking for > > failure is all you can do with it. Same information as "Return false on > > failure". > > > > If the contract is "Return negative errno on failure", the function is > > responsible for returning values that make sense. Ideally, the contract > > spells them all out. > > > > Do you know an example in code where we have both errno return value > and errp, and the return value make sense and used by callers? If there are examples of that, I would generally consider them to be bugs. IMHO if a method is using "Error **errp", then it should be considered forbidden to return 'errno' values. If there is a need for distinguishing some cases from others, then keep with int '0/-1' example, but turn it into a multi-value return such as 1/0/-1, or 0/-1/-2/-3/..., etc with named constants for the unusual scenarios. An example of that would be QIOChannel were we introduced "#define QIO_CHANNEL_ERR_BLOCK -2" to replace the need for EAGAIN checks in callers. 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 :|