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 D88C8C3A5A2 for ; Tue, 10 Sep 2019 13:00:52 +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 A7DC620872 for ; Tue, 10 Sep 2019 13:00:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A7DC620872 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]:39526 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i7flJ-00012E-TF for qemu-devel@archiver.kernel.org; Tue, 10 Sep 2019 09:00:50 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:32939) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i7fam-0000ff-HO for qemu-devel@nongnu.org; Tue, 10 Sep 2019 08:49:57 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i7fal-0000ue-CD for qemu-devel@nongnu.org; Tue, 10 Sep 2019 08:49:56 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56070) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1i7fai-0000t5-Oo; Tue, 10 Sep 2019 08:49:52 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 182DE3084025; Tue, 10 Sep 2019 12:49:52 +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 0A4F160852; Tue, 10 Sep 2019 12:49:50 +0000 (UTC) Date: Tue, 10 Sep 2019 14:49:49 +0200 From: Kevin Wolf To: Max Reitz Message-ID: <20190910124949.GG4446@localhost.localdomain> References: <20190809161407.11920-1-mreitz@redhat.com> <20190809161407.11920-21-mreitz@redhat.com> <20190910115620.GE4446@localhost.localdomain> <4fd84192-0078-07e9-b972-2f10030fb15f@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="C1iGAkRnbeBonpVg" Content-Disposition: inline In-Reply-To: <4fd84192-0078-07e9-b972-2f10030fb15f@redhat.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.40]); Tue, 10 Sep 2019 12:49:52 +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" --C1iGAkRnbeBonpVg Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Am 10.09.2019 um 14:04 hat Max Reitz geschrieben: > On 10.09.19 13:56, Kevin Wolf wrote: > > 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 the= re > >> is more than one such child. > >> > >> bdrv_snapshot_goto() becomes a bit weird because we may have to redire= ct > >> 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(BlockDrive= rState *bs, > >> return ret; > >> } > >> =20 > >> +/** > >> + * 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 =3D NULL; > >> + BdrvChild *child; > >> + > >> + QLIST_FOREACH(child, &bs->children, next) { > >> + if (child =3D=3D 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 multip= le */ > >> + return NULL; > >> + } > >> + child_bs =3D child->bs; > >> + } > >> + > >> + return child_bs; > >> +} > >=20 > > 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? >=20 > What would you return instead? &child doesn=E2=80=99t work. Oops, brain fart. :-) > We could limit ourselves to bs->file and bs->backing. It just seemed > like a bit of an artificial limit to me, because we only really have it > for bdrv_snapshot_goto(). Hm, but then, what use is supporting other children for creating a snapshot when you can't load it any more afterwards? Kevin --C1iGAkRnbeBonpVg Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIcBAEBAgAGBQJdd5vtAAoJEH8JsnLIjy/WxOcQALuNNHha3Cz3eRjzT2Gt3xXv ncGK5MiVeTA1wLZSDws4I3WgP7ymZaDjl/hBdRHh5BatY9/FnMJa7gcB9jZiRrHw IGGDw+493AdoWBhLm2bumMHSJ1sjQwcc8W9l7mLM9I7JIA2BArnEmW/wl3XNDFzE 59y13dwKiv7Dt3EsfHYcvkjneopO9683SMHcQ7Pz8UHLZFGvCLn7M5XLIPeet6s8 y87dgoOzPF6TKPkNIDrNur1LBqZdvlArxwXokWQ97ipsFJuzQHC2ONO7j6bkCBKH 77Qc857mrQSc9eurj9vxtfo9PxbnJ1kr4186cTENnS49MvO67eKdnlCUNvT1kx16 BnJ20eP5kFQwLWXkpVF8ycA9BhINGyIFxCrOXG2b5+dNlK7pkTK9+lI/Y1fKUPrK vQHb7HvLjlcVp4jCqJiDqfLAAh/F+YuWxNxTWGnG1p+t4NVwegvDw3lcJqCxeTEm kQ1p/RcMaY76bWWD4MkRv5qV9akGb16aijB1vssey5gra/wyXzoB77jXiBNeoYq5 4OQEIVPumEt9J0YyrTX1HyXmao/43gO1cqcVGJUDah4k7LM+XBKMDeeNcS+XSinG 0vv0cgF9TfTb18rDjutLnEg2kwGIWSHYICi4++ahL5lLxXBPkpCMWq+dTVUMPhND 3JT+EIm1k6YmQqndkNIm =xP7G -----END PGP SIGNATURE----- --C1iGAkRnbeBonpVg--