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Thu, 26 Sep 2019 11:26:04 +0000 (UTC) Subject: Re: [PATCH v13 00/15] backup-top filter driver for backup To: Vladimir Sementsov-Ogievskiy , "qemu-block@nongnu.org" References: <20190920142056.12778-1-vsementsov@virtuozzo.com> <9a0c66fe-f786-3f49-6fad-ffca04888659@virtuozzo.com> <16dc6262-06d7-29cf-a712-904f5a3c9627@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: Date: Thu, 26 Sep 2019 13:26:02 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.0 MIME-Version: 1.0 In-Reply-To: <16dc6262-06d7-29cf-a712-904f5a3c9627@virtuozzo.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="yFCEA11GXryeRUpjTNUVp1gY4iuBn2OoF" X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.49]); Thu, 26 Sep 2019 11:26:11 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 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: "fam@euphon.net" , "kwolf@redhat.com" , Denis Lunev , "wencongyang2@huawei.com" , "xiechanglong.d@gmail.com" , "armbru@redhat.com" , "qemu-devel@nongnu.org" , "jsnow@redhat.com" , "stefanha@redhat.com" 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) --yFCEA11GXryeRUpjTNUVp1gY4iuBn2OoF Content-Type: multipart/mixed; boundary="ZxsqMlpKxoSn3YdCStn961okVzh1Cl1Bd" --ZxsqMlpKxoSn3YdCStn961okVzh1Cl1Bd Content-Type: text/plain; charset=UTF-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 25.09.19 21:28, Vladimir Sementsov-Ogievskiy wrote: > ops, I've sent unfinished message >=20 > On 25.09.2019 22:19, Vladimir Sementsov-Ogievskiy wrote: >> Ogh :( >> >> And I realized that there is bigger problem with design: >> >> Assume failed copy in filter request: we want to mark bits dirty again= >> and release range lock on source.. But if we have some write reguests >> in parallel, they may already passed backup-top filter, and they are >> only waiting for range lock. When lock is free the will go on and will= >> not see bitmap changes.. >> >> That means that we can't use range lock: waiting request must wait on >> backup-top level, but range lock will not work on it, as they will >> interfer with original write request. >=20 > With such design we can't mark bits dirty again. We can switch to other= =20 > behavior: on failed block-copy in filter just cancel the whole=20 > block-job.. But actually I think both behaviors should be available for= =20 > user: > 1. if backup is important, better to fail guest writes if needed > 2. if guest is important, better to fail backup job if failed to do=20 > copy-before-write >=20 >> >> I have to rething it somehow, a kind of "intersecting requests" possib= ly >> will be kept. I still don't like that current backup write-notifier >> locks the whole region, even non-dirty bits, instead we should lock on= ly >> the region which we are handling at the moment. >> >> Patches 01-11 are still good themselves, as a preparation, let's keep = them >> >> Patches 12-13 are good, but range lock is not appropriate for backup..= >> May be they will be used for rewriting copy-on-read filter to copy in >> filter code.. Still I'm not sure, as COR should work through block-cop= y >> finally, and may possibly reuse same locking. >=20 > better drop 12-13 for now >=20 > Patch 14 is good, let's keep it. It has correct abort() in=20 > backup_top_cbw(), it's not dependent on 12-13, and it's waiting for=20 > corrected combining of backup-top, backup and block-copy. >=20 > And patch 15 is bad, I'll rewrite it. So, 16 is not needed too. I=E2=80=99ll drop 12 =E2=80=93 15. 14 is dead code without 15, so I=E2=80= =99d rather not keep it, actually. 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