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 A4C10C433EF for ; Wed, 12 Jan 2022 17:27:24 +0000 (UTC) Received: from localhost ([::1]:50814 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1n7hP9-00064Y-Mw for qemu-devel@archiver.kernel.org; Wed, 12 Jan 2022 12:27:23 -0500 Received: from eggs.gnu.org ([209.51.188.92]:46300) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1n7h91-0004cq-IW for qemu-devel@nongnu.org; Wed, 12 Jan 2022 12:10:43 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:29125) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1n7h8y-00054i-Tg for qemu-devel@nongnu.org; Wed, 12 Jan 2022 12:10:42 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1642007440; 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=ydb/3epK+zwrM8C2EGZE9gqqkKj8XQ6XC+dTPPKR+gY=; b=PxpNGoVDlVvq4C4wLJhzV3Kc5MVfPHiR3AkFI0fUvApQXok034oVKwYz279WPHMC3XuPNn riahayu9Axv4z0CQhTc8LMyo8vcbyhj9MV7D9RZdt9V0nEcmQC7r7t4tlzVca2KDbDjMTl J0ATVG/tlfWRAFbn5XSKZIH0dsAoWU0= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-591-PAozEYDYM8OqFJO52Xeyng-1; Wed, 12 Jan 2022 12:10:34 -0500 X-MC-Unique: PAozEYDYM8OqFJO52Xeyng-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id F22CD190B2A1; Wed, 12 Jan 2022 17:10:32 +0000 (UTC) Received: from redhat.com (unknown [10.39.195.78]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 32A1826DE0; Wed, 12 Jan 2022 17:10:25 +0000 (UTC) Date: Wed, 12 Jan 2022 18:10:23 +0100 From: Kevin Wolf To: Vladimir Sementsov-Ogievskiy Subject: Re: [PATCH v2] block: drop BLK_PERM_GRAPH_MOD Message-ID: References: <20210902093754.2352-1-vsementsov@virtuozzo.com> MIME-Version: 1.0 In-Reply-To: <20210902093754.2352-1-vsementsov@virtuozzo.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=kwolf@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=170.10.129.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -33 X-Spam_score: -3.4 X-Spam_bar: --- X-Spam_report: (-3.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.595, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=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: , Cc: ehabkost@redhat.com, qemu-block@nongnu.org, jsnow@redhat.com, armbru@redhat.com, qemu-devel@nongnu.org, hreitz@redhat.com, crosa@redhat.com, eblake@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 02.09.2021 um 11:37 hat Vladimir Sementsov-Ogievskiy geschrieben: > First, this permission never protected a node from being changed, as > generic child-replacing functions don't check it. > > Second, it's a strange thing: it presents a permission of parent node > to change its child. But generally, children are replaced by different > mechanisms, like jobs or qmp commands, not by nodes. > > Graph-mod permission is hard to understand. All other permissions > describe operations which done by parent node on its child: read, > write, resize. Graph modification operations are something completely > different. > > The only place where BLK_PERM_GRAPH_MOD is used as "perm" (not shared > perm) is mirror_start_job, for s->target. Still modern code should use > bdrv_freeze_backing_chain() to protect from graph modification, if we > don't do it somewhere it may be considered as a bug. So, it's a bit > risky to drop GRAPH_MOD, and analyzing of possible loss of protection > is hard. But one day we should do it, let's do it now. > > One more bit of information is that locking the corresponding byte in > file-posix doesn't make sense at all. > > Signed-off-by: Vladimir Sementsov-Ogievskiy Thanks, applied to the block branch. Kevin