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 X-Spam-Level: X-Spam-Status: No, score=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3FF91C433DB for ; Thu, 11 Mar 2021 17:20:00 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 95FFB64FE5 for ; Thu, 11 Mar 2021 17:19:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 95FFB64FE5 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:37560 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lKOyc-0006dG-At for qemu-devel@archiver.kernel.org; Thu, 11 Mar 2021 12:19:58 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:59600) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lKOov-0005Ii-Q5 for qemu-devel@nongnu.org; Thu, 11 Mar 2021 12:09:58 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:37424) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lKOos-0004vv-SB for qemu-devel@nongnu.org; Thu, 11 Mar 2021 12:09:57 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1615482593; 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=12MOtvDdtPTBcHloFL+KKCYlpALhhZswH+gA6Jk+OeI=; b=VCWJQdbev2QE20Dt9yRv9/MDZNug3WkIWJeobzAXZOLDUMsyZhCsKOGvGFm8T4YHfgOVuh SmrLdusY6B63D96k0f7xEvQ9ZBieMVdMzyoqSLbSZJJ9iUxT/IT/npwO2eY5IpcbGWk2rt dHevrN3ql329sc6BFbRs2Hf5IT2oRkE= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-411-F1X8isuLNFCz7TgCzgV1RQ-1; Thu, 11 Mar 2021 12:09:50 -0500 X-MC-Unique: F1X8isuLNFCz7TgCzgV1RQ-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id B9817100C668; Thu, 11 Mar 2021 17:09:48 +0000 (UTC) Received: from merkur.fritz.box (ovpn-114-112.ams2.redhat.com [10.36.114.112]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 777B15C255; Thu, 11 Mar 2021 17:09:47 +0000 (UTC) Date: Thu, 11 Mar 2021 18:09:46 +0100 From: Kevin Wolf To: Vladimir Sementsov-Ogievskiy Subject: Re: [PATCH RFC 0/3] block: drop inherits_from Message-ID: <20210311170946.GG9008@merkur.fritz.box> References: <20210311151505.206534-1-vsementsov@virtuozzo.com> MIME-Version: 1.0 In-Reply-To: <20210311151505.206534-1-vsementsov@virtuozzo.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 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=216.205.24.124; envelope-from=kwolf@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=-0.25, 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=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: den@openvz.org, jsnow@redhat.com, qemu-devel@nongnu.org, qemu-block@nongnu.org, mreitz@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 11.03.2021 um 16:15 hat Vladimir Sementsov-Ogievskiy geschrieben: > Hi all! > > I now work on v3 for "block: update graph permissions update", and I'm > at "[PATCH v2 28/36] block: add bdrv_set_backing_noperm() transaction > action". > > So, the problem is we should handle inherits_from carefully, and most > probably it should be updated in bdrv_replace_child_noperm().. And > then, bdrv_replace_child_noperm will become a transaction action, > which should store old inherits_from to the transaction state for > possible rollback.. Or something like this, I didn't try yet. I just > thought, may be we can just drop inherits_from? > > I decided to learn the thing a bit, and found that the only usage of > inherits_from is to limit reopen process. When adding bs to > reopen_queue we do add its children recursively, but only those which > inherits from the bs. > > That works so starting from > > commit 67251a311371c4d22e803f151f47fe817175b6c3 > Author: Kevin Wolf > Date: Thu Apr 9 18:54:04 2015 +0200 > > block: Fix reopen flag inheritance > > > The commit made two things: > > 1. reopen recursively all* children, not only .file. That's OK. > > 2. * : not all, but only that inherits_from bs. > > [2] Means that we don't reopen some implicitely created children.. > And, I want to ask, why? The reason is the difference between -drive if=none,file=test.qcow2 and something like -blockdev file,filename=backing.img,node-name=backing -blockdev file,filename=test.qcow2,node-name=file -blockdev qcow2,file=file,backing=backing The former means that bs->file and bs->backing inherit options from the qcow2 layer. If you reopen the qcow2 layer to set cache.direct=on, both children inherit the same update and both the file itself and the backing file will use O_DIRECT - this is the same as would happen if you had set cache.direct=on in the -drive option from the start. In the -blockdev case, the nodes were defined explicitly without inheriting from the qcow2 layer. Setting cache.direct=on on the qcow2 layer (which is actually created last) doesn't influence the two file layers. So a reopen of the qcow2 layer shouldn't change the two file nodes either: If they didn't inherit the option during bdrv_open(), they certainly shouldn't inherit it during bdrv_reopen() either. > For me it seems that if we have reopen process.. And bs involved. And > it has a child.. And child role defines how that child should inherit > options.. Why not to just inherit them? The -blockdev behaviour makes things a lot more predictable for a management tool for which we know that it can handle things on the node level. So what we really want is not inheriting at all. But compatibility with -drive doesn't let us. (And actually -blockdev with inline declaration of children behaves the same as -drive, which may have been a mistake.) Kevin