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Tue, 10 Sep 2019 12:04:50 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-117-90.ams2.redhat.com [10.36.117.90]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E7D8C5C226; Tue, 10 Sep 2019 12:04:48 +0000 (UTC) To: Kevin Wolf References: <20190809161407.11920-1-mreitz@redhat.com> <20190809161407.11920-21-mreitz@redhat.com> <20190910115620.GE4446@localhost.localdomain> From: Max Reitz Openpgp: preference=signencrypt Autocrypt: addr=mreitz@redhat.com; prefer-encrypt=mutual; keydata= mQENBFXOJlcBCADEyyhOTsoa/2ujoTRAJj4MKA21dkxxELVj3cuILpLTmtachWj7QW+TVG8U /PsMCFbpwsQR7oEy8eHHZwuGQsNpEtNC2G/L8Yka0BIBzv7dEgrPzIu+W3anZXQW4702+uES U29G8TP/NGfXRRHGlbBIH9KNUnOSUD2vRtpOLXkWsV5CN6vQFYgQfFvmp5ZpPeUe6xNplu8V mcTw8OSEDW/ZnxJc8TekCKZSpdzYoxfzjm7xGmZqB18VFwgJZlIibt1HE0EB4w5GsD7x5ekh awIe3RwoZgZDLQMdOitJ1tUc8aqaxvgA4tz6J6st8D8pS//m1gAoYJWGwwIVj1DjTYLtABEB AAG0HU1heCBSZWl0eiA8bXJlaXR6QHJlZGhhdC5jb20+iQFTBBMBCAA9AhsDBQkSzAMABQsJ CAcCBhUICQoLAgQWAgMBAh4BAheABQJVzie5FRhoa3A6Ly9rZXlzLmdudXBnLm5ldAAKCRD0 B9sAYdXPQDcIB/9uNkbYEex1rHKz3mr12uxYMwLOOFY9fstP5aoVJQ1nWQVB6m2cfKGdcRe1 2/nFaHSNAzT0NnKz2MjhZVmcrpyd2Gp2QyISCfb1FbT82GMtXFj1wiHmPb3CixYmWGQUUh+I AvUqsevLA+WihgBUyaJq/vuDVM1/K9Un+w+Tz5vpeMidlIsTYhcsMhn0L9wlCjoucljvbDy/ 8C9L2DUdgi3XTa0ORKeflUhdL4gucWoAMrKX2nmPjBMKLgU7WLBc8AtV+84b9OWFML6NEyo4 4cP7cM/07VlJK53pqNg5cHtnWwjHcbpGkQvx6RUx6F1My3y52vM24rNUA3+ligVEgPYBuQEN BFXOJlcBCADAmcVUNTWT6yLWQHvxZ0o47KCP8OcLqD+67T0RCe6d0LP8GsWtrJdeDIQk+T+F xO7DolQPS6iQ6Ak2/lJaPX8L0BkEAiMuLCKFU6Bn3lFOkrQeKp3u05wCSV1iKnhg0UPji9V2 W5eNfy8F4ZQHpeGUGy+liGXlxqkeRVhLyevUqfU0WgNqAJpfhHSGpBgihUupmyUg7lfUPeRM DzAN1pIqoFuxnN+BRHdAecpsLcbR8sQddXmDg9BpSKozO/JyBmaS1RlquI8HERQoe6EynJhd 64aICHDfj61rp+/0jTIcevxIIAzW70IadoS/y3DVIkuhncgDBvGbF3aBtjrJVP+5ABEBAAGJ ASUEGAEIAA8FAlXOJlcCGwwFCRLMAwAACgkQ9AfbAGHVz0CbFwf9F/PXxQR9i4N0iipISYjU sxVdjJOM2TMut+ZZcQ6NSMvhZ0ogQxJ+iEQ5OjnIputKvPVd5U7WRh+4lF1lB/NQGrGZQ1ic alkj6ocscQyFwfib+xIe9w8TG1CVGkII7+TbS5pXHRxZH1niaRpoi/hYtgzkuOPp35jJyqT/ /ELbqQTDAWcqtJhzxKLE/ugcOMK520dJDeb6x2xVES+S5LXby0D4juZlvUj+1fwZu+7Io5+B bkhSVPb/QdOVTpnz7zWNyNw+OONo1aBUKkhq2UIByYXgORPFnbfMY7QWHcjpBVw9MgC4tGeF R4bv+1nAMMxKmb5VvQCExr0eFhJUAHAhVg== Message-ID: <4fd84192-0078-07e9-b972-2f10030fb15f@redhat.com> Date: Tue, 10 Sep 2019 14:04:47 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190910115620.GE4446@localhost.localdomain> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="8tdC790XFil8lYgpiZzbns5y8NZvzTS9Q" X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.42]); Tue, 10 Sep 2019 12:04:50 +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" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --8tdC790XFil8lYgpiZzbns5y8NZvzTS9Q Content-Type: multipart/mixed; boundary="J1lvGwE78SNvvK6CBPCBrYlyO1iODg7kz"; protected-headers="v1" From: Max Reitz To: Kevin Wolf Cc: qemu-block@nongnu.org, qemu-devel@nongnu.org, Vladimir Sementsov-Ogievskiy Message-ID: <4fd84192-0078-07e9-b972-2f10030fb15f@redhat.com> Subject: Re: [PATCH v6 20/42] block/snapshot: Fix fallback References: <20190809161407.11920-1-mreitz@redhat.com> <20190809161407.11920-21-mreitz@redhat.com> <20190910115620.GE4446@localhost.localdomain> In-Reply-To: <20190910115620.GE4446@localhost.localdomain> --J1lvGwE78SNvvK6CBPCBrYlyO1iODg7kz Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable 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 w= e >> 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 fo= r > the other functions that only need a BDS? What would you return instead? &child doesn=E2=80=99t work. 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(). Max --J1lvGwE78SNvvK6CBPCBrYlyO1iODg7kz-- --8tdC790XFil8lYgpiZzbns5y8NZvzTS9Q Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl13kV8ACgkQ9AfbAGHV z0AMdgf8DtLHKXlucaopAqKmX8y1SiAnDXMkT9QUbpibl5rMLcend5Grg24Pr2KN P4etxvJQDnG368pafpF3kmdTj7/gZm5VQaZg2njCS6ZHaSjDtBHg/CUsooSpYsiZ nMfJ7wFrJtIsvXNr+KzAUWzmrSAOge+WTIaQr7d782R7taHbCCvAj1Ny0Om9C1PD WLo7vhA9h7ToMGVOBCQ4D33aMl2/H6tP95Jmz57m6tbwH5QpvAzzcHp41C9C8ypK BeAeI6+qLPB1blRQjxbc5XOs8Am4zJNGeR84MgipW+Xr4MZBfWBp74IIXmprUVl9 FvpvyEp0wv+kEE9Kkn824GycdkijvQ== =n4RD -----END PGP SIGNATURE----- --8tdC790XFil8lYgpiZzbns5y8NZvzTS9Q--