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=-13.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 D3C7BC433ED for ; Wed, 5 May 2021 14:06:58 +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 18C7861182 for ; Wed, 5 May 2021 14:06:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 18C7861182 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]:50728 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1leIAy-0000cc-Um for qemu-devel@archiver.kernel.org; Wed, 05 May 2021 10:06:56 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:37800) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1leI3P-0003BI-Fr for qemu-devel@nongnu.org; Wed, 05 May 2021 09:59:07 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:59926) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1leI3N-0005tC-QX for qemu-devel@nongnu.org; Wed, 05 May 2021 09:59:07 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1620223145; 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=rAN9nD23xbwyUjOIKVQBbmB525RcJckVSUYgg5gP/NA=; b=abkm0PoGFit6XelC/NeYKa9iKKhdlHOkESvCcShzLCuphrOwVHtAkEKNpB1pEjDXUjAW9I 4FqUwVuVM0Yst1BTJZr5O54t3gFpxSZkbQvIheCiOAYwjwfgL7Xis4J1o6kFb9Ag26eIdd Pe+E8ajzMFEnRNstXRM8dHk94NoSFTQ= 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-168-EtCzI3JSNf2AV2sWZpzfHQ-1; Wed, 05 May 2021 09:59:01 -0400 X-MC-Unique: EtCzI3JSNf2AV2sWZpzfHQ-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id B342A1B18BC8; Wed, 5 May 2021 13:59:00 +0000 (UTC) Received: from merkur.fritz.box (ovpn-115-138.ams2.redhat.com [10.36.115.138]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 9948A10074E5; Wed, 5 May 2021 13:58:59 +0000 (UTC) Date: Wed, 5 May 2021 15:58:57 +0200 From: Kevin Wolf To: Alberto Garcia Subject: Re: [PATCH v4 2/6] block: Allow changing bs->file on reopen Message-ID: References: <31ccb1061199ee11bf9879f6c60608a19b83263d.1616000692.git.berto@igalia.com> MIME-Version: 1.0 In-Reply-To: <31ccb1061199ee11bf9879f6c60608a19b83263d.1616000692.git.berto@igalia.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 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=170.10.133.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.693, 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_H4=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: Vladimir Sementsov-Ogievskiy , qemu-devel@nongnu.org, qemu-block@nongnu.org, Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 17.03.2021 um 18:15 hat Alberto Garcia geschrieben: > When the x-blockdev-reopen was added it allowed reconfiguring the > graph by replacing backing files, but changing the 'file' option was > forbidden. Because of this restriction some operations are not > possible, notably inserting and removing block filters. > > This patch adds support for replacing the 'file' option. This is > similar to replacing the backing file and the user is likewise > responsible for the correctness of the resulting graph, otherwise this > can lead to data corruption. > > Signed-off-by: Alberto Garcia > @@ -4238,13 +4254,13 @@ static int bdrv_reopen_parse_backing(BDRVReopenState *reopen_state, > } > > /* If we want to replace the backing file we need some extra checks */ > - if (new_backing_bs != bdrv_filter_or_cow_bs(overlay_bs)) { > + if (new_child_bs != bdrv_filter_or_cow_bs(overlay_bs)) { I may be missing something, but I don't see how this whole block makes sense for changing 'file'. overlay_bs was found by going down the backing chain, so of course it will be different from new_child_bs (unless you use the same node as 'backing' and as 'file'). So we run all this code that seems to be concerned only with backing files. Probably overlay_bs should be found by starting from child and using bdrv_filter_or_cow_bs() only for the following loop iterations. > int ret; > > /* Check for implicit nodes between bs and its backing file */ > if (bs != overlay_bs) { > - error_setg(errp, "Cannot change backing link if '%s' has " > - "an implicit backing file", bs->node_name); > + error_setg(errp, "Cannot change %s link if '%s' has an implicit " > + "child", parse_file ? "file" : "backing", bs->node_name); > return -EPERM; > } With fixed overlay_bs, this check makes sense, though the comment needs an update. > /* > @@ -4256,16 +4272,24 @@ static int bdrv_reopen_parse_backing(BDRVReopenState *reopen_state, > * with bs->drv->supports_backing == true. > */ > if (bdrv_is_backing_chain_frozen(overlay_bs, > - child_bs(overlay_bs->backing), errp)) > + bdrv_filter_or_cow_bs(overlay_bs), > + errp)) > { > return -EPERM; > } This checks if bs->backing is frozen (overlay_bs == bs because of the check above). What we really want to check is if child is frozen (i.e. bs->backing for updating 'backing', bs->file for updating 'file). So maybe this should be just written as that: if (child && child->frozen) { error_setg(errp, ...); return -EPERM; } Or factor this part out from bdrv_is_backing_chain_frozen() into a bdrv_is_child_frozen() or something like that. Either way, this might make the whole (outdated) comment above unnecessary because things would become a lot clearer. > - reopen_state->replace_backing_bs = true; > - reopen_state->old_backing_bs = bs->backing ? bs->backing->bs : NULL; > - ret = bdrv_set_backing_noperm(bs, new_backing_bs, set_backings_tran, > - errp); > - if (ret < 0) { > - return ret; > + if (parse_file) { > + /* Store the old file bs, we'll need to refresh its permissions */ > + reopen_state->old_file_bs = bs->file->bs; > + > + /* And finally replace the child */ > + bdrv_replace_child(bs->file, new_child_bs, tran); > + } else { > + reopen_state->replace_backing_bs = true; > + reopen_state->old_backing_bs = child_bs(bs->backing); > + ret = bdrv_set_backing_noperm(bs, new_child_bs, tran, errp); > + if (ret < 0) { > + return ret; > + } > } > } Kevin