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=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 B94A5C3A5A2 for ; Tue, 10 Sep 2019 11:58:19 +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 8E8DD2084D for ; Tue, 10 Sep 2019 11:58:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8E8DD2084D 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]:38514 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i7emo-0000yf-OR for qemu-devel@archiver.kernel.org; Tue, 10 Sep 2019 07:58:18 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:50647) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i7el5-00086g-CT for qemu-devel@nongnu.org; Tue, 10 Sep 2019 07:56:32 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i7el4-0007n2-98 for qemu-devel@nongnu.org; Tue, 10 Sep 2019 07:56:31 -0400 Received: from mx1.redhat.com ([209.132.183.28]:33252) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1i7el2-0007j1-4P; Tue, 10 Sep 2019 07:56:28 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 4A1D41DC8; Tue, 10 Sep 2019 11:56:27 +0000 (UTC) Received: from localhost.localdomain (ovpn-116-217.ams2.redhat.com [10.36.116.217]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3CD655D9D6; Tue, 10 Sep 2019 11:56:22 +0000 (UTC) Date: Tue, 10 Sep 2019 13:56:20 +0200 From: Kevin Wolf To: Max Reitz Message-ID: <20190910115620.GE4446@localhost.localdomain> References: <20190809161407.11920-1-mreitz@redhat.com> <20190809161407.11920-21-mreitz@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190809161407.11920-21-mreitz@redhat.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.71]); Tue, 10 Sep 2019 11:56:27 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH v6 20/42] block/snapshot: Fix fallback 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 Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 09.08.2019 um 18:13 hat Max Reitz geschrieben: > If the top node's driver does not provide snapshot functionality and we > want to fall back to a node down the chain, we need to snapshot all > non-COW children. For simplicity's sake, just do not fall back if there > is more than one such child. > > bdrv_snapshot_goto() becomes a bit weird because we may have to redirect > the actual child pointer, so it only works if the fallback child is > bs->file or bs->backing (and then we have to find out which it is). > > Suggested-by: Vladimir Sementsov-Ogievskiy > Signed-off-by: Max Reitz > --- > block/snapshot.c | 100 +++++++++++++++++++++++++++++++++++++---------- > 1 file changed, 79 insertions(+), 21 deletions(-) > > diff --git a/block/snapshot.c b/block/snapshot.c > index f2f48f926a..35403c167f 100644 > --- a/block/snapshot.c > +++ b/block/snapshot.c > @@ -146,6 +146,32 @@ bool bdrv_snapshot_find_by_id_and_name(BlockDriverState *bs, > return ret; > } > > +/** > + * Return the child BDS to which we can fall back if the given BDS > + * does not support snapshots. > + * Return NULL if there is no BDS to (safely) fall back to. > + */ > +static BlockDriverState *bdrv_snapshot_fallback(BlockDriverState *bs) > +{ > + BlockDriverState *child_bs = NULL; > + BdrvChild *child; > + > + QLIST_FOREACH(child, &bs->children, next) { > + if (child == bdrv_filtered_cow_child(bs)) { > + /* Ignore: COW children need not be included in snapshots */ > + continue; > + } > + > + if (child_bs) { > + /* Cannot fall back to a single child if there are multiple */ > + return NULL; > + } > + child_bs = child->bs; > + } > + > + return child_bs; > +} Why do we return child->bs here when bdrv_snapshot_goto() then needs to reconstruct what the associated BdrvChild was? Wouldn't it make more sense to return BdrvChild** from here and maybe have a small wrapper for the other functions that only need a BDS? Kevin