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 487F7C28B30 for ; Thu, 20 Mar 2025 11:31:52 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1tvE6y-0003Zf-Bp; Thu, 20 Mar 2025 07:31:11 -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 1tvE6g-0003Ym-AL for qemu-devel@nongnu.org; Thu, 20 Mar 2025 07:30:38 -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 1tvE6c-0000bA-W3 for qemu-devel@nongnu.org; Thu, 20 Mar 2025 07:30:37 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1742470232; 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=DIQHmzmLdPE+h+jSjUJtPaYaIPpGC0D+zcpElNjNaI8=; b=TEPL3ngMVrAyECDiq+kCl/KxpvdQnNpJ5Gde5HiABNkGJ7V3hxWNhe//bpyuB9+Va7G91A 4iPaf8MuE84VGJXbtiYWG+BOPi1ICFWUITvK4D9vnf9uorJNTmOxEmi1Rv9N2Y3kfxAg83 5j4IngW0CL99BC638DDLBT1jQPFcq1k= Received: from mx-prod-mc-01.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-498-cylvoJe1NNK06jNCjpdRHA-1; Thu, 20 Mar 2025 07:30:27 -0400 X-MC-Unique: cylvoJe1NNK06jNCjpdRHA-1 X-Mimecast-MFC-AGG-ID: cylvoJe1NNK06jNCjpdRHA_1742470226 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-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 849F1196D2D0; Thu, 20 Mar 2025 11:30:25 +0000 (UTC) Received: from redhat.com (unknown [10.45.225.84]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 90A54180094A; Thu, 20 Mar 2025 11:30:21 +0000 (UTC) Date: Thu, 20 Mar 2025 12:30:18 +0100 From: Kevin Wolf To: Markus Armbruster Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, hreitz@redhat.com, vsementsov@yandex-team.ru Subject: Re: [PATCH] block: Fix bdrv_activate() not to fail without medium Message-ID: References: <20250312143758.1660177-1-armbru@redhat.com> <87tt7x87um.fsf@pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87tt7x87um.fsf@pond.sub.org> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Received-SPF: pass client-ip=170.10.133.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -23 X-Spam_score: -2.4 X-Spam_bar: -- X-Spam_report: (-2.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.332, 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_H2=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=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 Am 13.03.2025 um 12:53 hat Markus Armbruster geschrieben: > Kevin Wolf writes: > > > Am 12.03.2025 um 15:37 hat Markus Armbruster geschrieben: > >> bdrv_activate() returns failure without setting an error when > >> !bs->drv. This is suspicious. Turns out it used to succeed then, > >> until commit 5416645fcf82 changed it to return -ENOMEDIUM. > >> > >> Return zero instead. > >> > >> Fixes: 5416645fcf82 (block: return error-code from bdrv_invalidate_cache) > >> Signed-off-by: Markus Armbruster > > > > The commit message sounds more theoretical. Did you find this only by > > code inspection? Do we know what the effect on real-world cases is, so > > we could add a sentence about it to the commit message? Maybe we could > > even have a qemu-iotests case to show the effect? > > > > I absolutely agree that returning -ENOMEDIUM while not setting errp is > > wrong. But without an example of what is affected, it's not obvious to > > me which part of it needs to be fixed. > > Code inspection. > > Here's my somewhat extended rationale for my fix. > [...] > Not failing the function on !bs->drv is clearly intentional. > > Behavior stayed this way for more than six years. Then commit > 5416645fcf8 (block: return error-code from bdrv_invalidate_cache) > changed the function to return zero on success, a negative errno on > failure. According to the commit message, the patch is mere cleanup, > and not supposed to change behavior. > > Since the first return was a success before the patch (no error set), > the correct value to return was zero. The patch used -ENOMEDIUM > instead. This is a clear regression. > > My patch restores previous behavior. I understand your rationale and don't disagree with your patch. But I would still like the commit message to explain the practical consequences of the bug and if possible a test case. If you tried to find the practical consequences and couldn't find any way to trigger a bug as a user, that is worth documenting, too. Kevin