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 6763BC87FCB for ; Sat, 9 Aug 2025 08:31:50 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ukeyt-0004Ne-S2; Sat, 09 Aug 2025 04:31:11 -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 1ukeyo-0004Lh-Gk for qemu-devel@nongnu.org; Sat, 09 Aug 2025 04:31:07 -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 1ukeyk-0003oG-At for qemu-devel@nongnu.org; Sat, 09 Aug 2025 04:31:06 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1754728258; 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: in-reply-to:in-reply-to:references:references; bh=jA9XqTlFb6oLGRfX0QHBtY9/IrRsSFr4peKr9LTWWew=; b=bMdrTv5q8RmlVXV5W7fk28UVYZO3tCgfDg5+MwfZilSacDXWLRMhgjrr2U446fvfZFuzrT lBPES3dLZYstbVwma5D2Idrk4RJ7BDLnJB5c28T/5dq9oqPufpjSWfj5sgw08RqehPdS5i AFo/6AYMxAMUyo/QolIrbbV8ZlxjTtc= 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-360-a6rOb7XvPau4dT3skaC9GQ-1; Sat, 09 Aug 2025 04:30:56 -0400 X-MC-Unique: a6rOb7XvPau4dT3skaC9GQ-1 X-Mimecast-MFC-AGG-ID: a6rOb7XvPau4dT3skaC9GQ_1754728256 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (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 0D28E19560AA; Sat, 9 Aug 2025 08:30:56 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.45.242.18]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 9FB0F19560AD; Sat, 9 Aug 2025 08:30:55 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id E76B221E6A27; Sat, 09 Aug 2025 10:30:52 +0200 (CEST) From: Markus Armbruster To: Akihiko Odaki Cc: qemu-devel@nongnu.org, marcandre.lureau@redhat.com Subject: Re: [PATCH 12/12] error: Kill @error_warn In-Reply-To: (Akihiko Odaki's message of "Sat, 9 Aug 2025 16:07:54 +0900") References: <20250808080823.2638861-1-armbru@redhat.com> <20250808080823.2638861-13-armbru@redhat.com> Date: Sat, 09 Aug 2025 10:30:52 +0200 Message-ID: <875xewucar.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 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: -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_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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Akihiko Odaki writes: > On 2025/08/08 17:08, Markus Armbruster wrote: >> We added @error_warn some two years ago in commit 3ffef1a55ca (error: >> add global &error_warn destination). It has multiple issues: >> >> * error.h's big comment was not updated for it. >> >> * Function contracts were not updated for it. >> >> * ERRP_GUARD() is unaware of @error_warn, and fails to mask it from >> error_prepend() and such. These crash on @error_warn, as pointed >> out by Akihiko Odaki. >> >> All fixable. However, after more than two years, we had just of 15 >> uses, of which the last few patches removed eight as unclean or >> otherwise undesirable. I didn't look closely enough at the remaining >> seven to decide whether they are desirable or not. >> >> I don't think this feature earns its keep. Drop it. > > I want to note that the following patch series temporarily use &error_warn during its conversion to add errp parameters: > https://lore.kernel.org/qemu-devel/20250808-propagate_tpm_error-v10-0-3e81a1d419b2@redhat.com/ > ("[PATCH v10 00/27] migration: propagate vTPM errors using Error objects") > > I think this series needs to be rebased on top of the migration change. Thanks for the heads-up. > I'm not sure if seven uses are insufficient to keep it. > > I also have a general impression that perhaps a special error destination for error_report_err() is more useful. Today, there are many functions use Error, but there are also functions that still follow old error handling patterns. When legacy functions call functions with Error, a common pattern is to use error_report_err() and return -1. You mean like &error_fatal less the exit(1)? > "[PATCH 01/12] monitor: Clean up HMP gdbserver error reporting" and "[PATCH 09/12] ui/pixman: Consistent error handling in qemu_pixman_shareable_free()" are examples that will benefit from error_report_err() as an error destination. The migration patch series I mentioned earlier can also use one. > > Perhaps it is nicer if there is an infrastructure shared by the special destinations. In particular, we can have common solutions for the three problems you pointed out: > >> * error.h's big comment was not updated for it. >> >> * Function contracts were not updated for it. > > For these two problems, they can refer to "special error destinations" instead of listing them, and delegate explanations of them to corresponding ones. > >> >> * ERRP_GUARD() is unaware of @error_warn, and fails to mask it from >> error_prepend() and such. These crash on @error_warn, as pointed >> out by Akihiko Odaki. > > For this problem, Error can tell that it is a special destination by leaving msg NULL, for example. ERRP_GUARD() then rewrites errp it is not &error_abort and msg is NULL. As I wrote, the defects are all fixable. However, there has been so little use of &error_warn, and so much of it has been unclean or otherwise undesirable. It's obviously prone to misuse. I think we're better off without it. See also the memo "Abuse of warnings for unhandled errors and programming errors" I posted yesterday. > Special destinations can also have a function pointer void (*)(Error*), which will be called by error_handle(). This way, we can ensure that having a special destination will not require changes to the common code. > > By the way, I also asked for a comment with the migration patch series. Please reply the following if you have anything to say: > https://lore.kernel.org/qemu-devel/9c552525-72fa-4d1e-89a2-b5c0e446935a@rsg.ci.i.u-tokyo.ac.jp/ > > There is also an additional context: > https://lore.kernel.org/qemu-devel/aJMsRBd9-XOMRG78@armenon-kvm.bengluru.csb/ I replied there. I'll be on vacation the next two weeks.