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Tue, 21 Jan 2020 13:29:23 +0000 (UTC) Subject: Re: [PATCH 2/2] iotests: add test for backup-top failure on permission activation To: Vladimir Sementsov-Ogievskiy , "qemu-block@nongnu.org" References: <20200116155452.30972-1-vsementsov@virtuozzo.com> <20200116155452.30972-3-vsementsov@virtuozzo.com> <0e865df2-7d21-b18f-b73c-2948577b9dcb@virtuozzo.com> <1313e55e-0eb1-890a-4e8e-2517f1e80d38@redhat.com> <04a32d71-31da-a3e3-5c5f-cc6465fc9402@virtuozzo.com> <6923bc19-d203-63af-b206-8fe18e4a01c6@redhat.com> <61b2915c-01fd-65ab-a5c0-5f2e089baf60@virtuozzo.com> From: Max Reitz 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: <0c12e6fc-3693-0663-13a2-56362c884520@redhat.com> Date: Tue, 21 Jan 2020 14:29:22 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.1 MIME-Version: 1.0 In-Reply-To: <61b2915c-01fd-65ab-a5c0-5f2e089baf60@virtuozzo.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="GbohHTnKiyIlqoRlw1pHAj3ekaVrsJYRz" X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.81 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: "kwolf@redhat.com" , "qemu-devel@nongnu.org" , "qemu-stable@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) --GbohHTnKiyIlqoRlw1pHAj3ekaVrsJYRz Content-Type: multipart/mixed; boundary="afHCjAOao4nKJjnvjEstLAnsbDW7PwiOd" --afHCjAOao4nKJjnvjEstLAnsbDW7PwiOd Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 21.01.20 13:53, Vladimir Sementsov-Ogievskiy wrote: > 21.01.2020 15:39, Max Reitz wrote: >> On 21.01.20 11:40, Vladimir Sementsov-Ogievskiy wrote: >>> 21.01.2020 12:41, Max Reitz wrote: >>>> On 21.01.20 10:23, Vladimir Sementsov-Ogievskiy wrote: >>>>> 21.01.2020 12:14, Max Reitz wrote: >>>>>> On 20.01.20 18:20, Vladimir Sementsov-Ogievskiy wrote: >>>>>>> 20.01.2020 20:04, Max Reitz wrote: >>>>>>>> On 16.01.20 16:54, Vladimir Sementsov-Ogievskiy wrote: >>>>>>>>> This test checks that bug is really fixed by previous commit. >>>>>>>>> >>>>>>>>> Cc: qemu-stable@nongnu.org # v4.2.0 >>>>>>>>> Signed-off-by: Vladimir Sementsov-Ogievskiy >>>>>>>>> --- >>>>>>>>> tests/qemu-iotests/283 | 75 ++++++++++++++++++++++++++++= ++++++++++ >>>>>>>>> tests/qemu-iotests/283.out | 8 ++++ >>>>>>>>> tests/qemu-iotests/group | 1 + >>>>>>>>> 3 files changed, 84 insertions(+) >>>>>>>>> create mode 100644 tests/qemu-iotests/283 >>>>>>>>> create mode 100644 tests/qemu-iotests/283.out >>>>>>>> >>>>>>>> The test looks good to me, I just have a comment nit and a note on= the >>>>>>>> fact that this should probably be queued only after Thomas=E2=80= =99s =E2=80=9CEnable >>>>>>>> more iotests during "make check-block"=E2=80=9D series. >>>>>>>> >>>>>>>>> diff --git a/tests/qemu-iotests/283 b/tests/qemu-iotests/283 >>>>>>>>> new file mode 100644 >>>>>>>>> index 0000000000..f0f216d109 >>>>>>>>> --- /dev/null >>>>>>>>> +++ b/tests/qemu-iotests/283 >>>>>>>>> @@ -0,0 +1,75 @@ >>>>>>>>> +#!/usr/bin/env python >>>>>>>>> +# >>>>>>>>> +# Test for backup-top filter permission activation failure >>>>>>>>> +# >>>>>>>>> +# Copyright (c) 2019 Virtuozzo International GmbH. >>>>>>>>> +# >>>>>>>>> +# This program is free software; you can redistribute it and/or = modify >>>>>>>>> +# it under the terms of the GNU General Public License as publis= hed by >>>>>>>>> +# the Free Software Foundation; either version 2 of the License,= or >>>>>>>>> +# (at your option) any later version. >>>>>>>>> +# >>>>>>>>> +# This program is distributed in the hope that it will be useful= , >>>>>>>>> +# but WITHOUT ANY WARRANTY; without even the implied warranty of >>>>>>>>> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the >>>>>>>>> +# GNU General Public License for more details. >>>>>>>>> +# >>>>>>>>> +# You should have received a copy of the GNU General Public Lice= nse >>>>>>>>> +# along with this program. If not, see . >>>>>>>>> +# >>>>>>>>> + >>>>>>>>> +import iotests >>>>>>>>> + >>>>>>>>> +# The test is unrelated to formats, restrict it to qcow2 to avoi= d extra runs >>>>>>>>> +iotests.verify_image_format(supported_fmts=3D['qcow2']) >>>>>>>>> + >>>>>>>>> +size =3D 1024 * 1024 >>>>>>>>> + >>>>>>>>> +""" >>>>>>>>> +On activation, backup-top is going to unshare write permission o= n its >>>>>>>>> +source child. It will be impossible for the following configurat= ion: >>>>>>>> >>>>>>>> =E2=80=9CThe following configuration will become impossible=E2=80= =9D? >>>>>>> >>>>>>> Hmm, no, the configuration is possible. But "it", i.e. "unshare wri= te permission", >>>>>>> is impossible with such configuration.. >>>>>> >>>>>> But backup_top always unshares the write permission on the source. >>>>> >>>>> Yes, and I just try to say, that this action will fail. And the test = checks that it >>>>> fails (and it crashes with current master instead of fail). >>>> >>>> OK. So what I was trying to say is that the comment currently only >>>> states that this will fail. I=E2=80=99d prefer it to also reassure me= that it=E2=80=99s >>>> correct that this fails (because all writes on the backup source must = go >>>> through backup_top), and that this is exactly what we want to test her= e. >>>> >>>> On first reading, I was wondering why exactly this comment would tell = me >>>> all these things, because I didn=E2=80=99t know what the test wants to= test in >>>> the first place. >>>> >>>> Max >>> >>> Hmm, something like: >>> >>> Backup wants to copy a point-in-time state of the source node. So, it c= atches all writes >>> to the source node by appending backup-top filter above it. So we handl= e all changes which >>> comes from source node parents. To prevent appearing of new writing par= ents during the >>> progress, backup-top unshares write permission on its source child. Thi= s has additional >>> implication: as this "unsharing" is propagated by default by backing/fi= le children, >>> backup-top conflicts with any side parents of source sub-tree with writ= e permission. >>> And this is in good relation with the general idea: with such parents w= e can't guarantee >>> point-in-time backup. >> >> Works for me (thanks :-)), but a shorter =E2=80=9CWhen performing a back= up, all >> writes on the source subtree must go through the backup-top filter so it >> can copy all data to the target before it is changed. Therefore, >> backup-top cannot allow other nodes to change data on its source child.= =E2=80=9D >> would work for me just as well. >=20 > Hmm, I don't like this "Therefore". For me the last statement > "cannot allow" doesn't looks like a consequence of the first > "all writes must go through", it more like rephrasing (still > not completely equal)... So, I'll keep my wording) I mean, you can just drop the second sentence, and then it gets even shorter... 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