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Thu, 20 Jun 2019 18:46:31 +0000 (UTC) Received: from dresden.str.redhat.com (unknown [10.40.205.208]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3731B60477; Thu, 20 Jun 2019 18:46:25 +0000 (UTC) To: John Snow , qemu-devel@nongnu.org, qemu-block@nongnu.org References: <20190620010356.19164-1-jsnow@redhat.com> <20190620010356.19164-3-jsnow@redhat.com> <5a873055-72c2-ac4c-074d-2c31c8b4c863@redhat.com> 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: <070fe637-f10f-0e3b-7fc3-e0ea1ecb6ae2@redhat.com> Date: Thu, 20 Jun 2019 20:46:23 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <5a873055-72c2-ac4c-074d-2c31c8b4c863@redhat.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="ttXvptYEExBvOeKWOJV27ICUiQW0KDkUU" X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Thu, 20 Jun 2019 18:46:39 +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 02/12] block/backup: Add mirror sync mode 'bitmap' 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: Kevin Wolf , Fam Zheng , vsementsov@virtuozzo.com, Wen Congyang , Xie Changlong , Markus Armbruster 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) --ttXvptYEExBvOeKWOJV27ICUiQW0KDkUU Content-Type: multipart/mixed; boundary="vgwFx0mYKSYUk9DlnyMB5IfQRvE4qpT6d"; protected-headers="v1" From: Max Reitz To: John Snow , qemu-devel@nongnu.org, qemu-block@nongnu.org Cc: Kevin Wolf , Fam Zheng , vsementsov@virtuozzo.com, Wen Congyang , Xie Changlong , Markus Armbruster Message-ID: <070fe637-f10f-0e3b-7fc3-e0ea1ecb6ae2@redhat.com> Subject: Re: [PATCH 02/12] block/backup: Add mirror sync mode 'bitmap' References: <20190620010356.19164-1-jsnow@redhat.com> <20190620010356.19164-3-jsnow@redhat.com> <5a873055-72c2-ac4c-074d-2c31c8b4c863@redhat.com> In-Reply-To: <5a873055-72c2-ac4c-074d-2c31c8b4c863@redhat.com> --vgwFx0mYKSYUk9DlnyMB5IfQRvE4qpT6d Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 20.06.19 18:01, John Snow wrote: >=20 >=20 > On 6/20/19 11:00 AM, Max Reitz wrote: >> On 20.06.19 03:03, John Snow wrote: >>> We don't need or want a new sync mode for simple differences in >>> semantics. Create a new mode simply named "BITMAP" that is designed = to >>> make use of the new Bitmap Sync Mode field. >>> >>> Because the only bitmap mode is 'conditional', this adds no new >>> functionality to the backup job (yet). The old incremental backup mod= e >>> is maintained as a syntactic sugar for sync=3Dbitmap, mode=3Dconditio= nal. >>> >>> Add all of the plumbing necessary to support this new instruction. >>> >>> Signed-off-by: John Snow >>> --- >>> qapi/block-core.json | 30 ++++++++++++++++++++++-------- >>> include/block/block_int.h | 6 +++++- >>> block/backup.c | 35 ++++++++++++++++++++++++++++------- >>> block/mirror.c | 6 ++++-- >>> block/replication.c | 2 +- >>> blockdev.c | 8 ++++++-- >>> 6 files changed, 66 insertions(+), 21 deletions(-) >>> >>> diff --git a/qapi/block-core.json b/qapi/block-core.json >>> index caf28a71a0..6d05ad8f47 100644 >>> --- a/qapi/block-core.json >>> +++ b/qapi/block-core.json >>> @@ -1127,12 +1127,15 @@ >>> # >>> # @none: only copy data written from now on >>> # >>> -# @incremental: only copy data described by the dirty bitmap. Since:= 2.4 >>> +# @incremental: only copy data described by the dirty bitmap. (since= : 2.4) >> >> Why not deprecate this in the process and note that this is equal to >> sync=3Dbitmap, bitmap-mode=3Dconditional? >> >> (I don=E2=80=99t think there is a rule that forces us to actually remo= ve >> deprecated stuff after two releases if it doesn=E2=80=99t hurt to keep= it.) >> >=20 > Mostly I thought it would be fine to keep as sugar. In your replies so > far I gather that "incremental" and "differential" don't mean specific > backup paradigms to you, so maybe these seem like worthless words. >=20 > It was my general understanding that in terms of backup > paradigms/methodologies that "incremental" and "differential" mean very= > specific things. >=20 > Incremental: Each backup contains only the delta from the last > incremental backup. > Differential: Each backup contains the delta from the last FULL backup.= >=20 > You can search "incremental vs differential backup" on your search > engine of choice and find many relevant results. I took a Networking/IT= > vocational degree in 2007 and these terms were taught in textbooks then= =2E >=20 > So I will resist quite strongly changing them, and for this reason, fel= t > that it was strictly a good thing to keep incremental as sugar, because= > I thought that people would know what it meant. :C OK. I=E2=80=99m happy as long as it=E2=80=99s all explained somewhere (i= =2Ee. bitmaps.rst). Personally, I=E2=80=99d also like a pointer to that docume= ntation here. (Sure, people should just look there if they don=E2=80=99t underst= and something about bitmaps anyway, but I can=E2=80=99t see it hurting to jus= t put a pointer here anyway.) > (More than "conditional", anyway, which is jargon I made up.) But you make it up in this series, which is great for me, because that means I get the definition (from the cover letter) without having to look it up. O:-) [...] >>> # >>> +# @bitmap-mode: Specifies the type of data the bitmap should contain= after >>> +# the operation concludes. Must be present if sync is = "bitmap". >>> +# Must NOT be present otherwise. (Since 4.1) >> >> Do we have any rule that qemu must enforce =E2=80=9Cmust not=E2=80=9Ds= ? :-) >> >> (No, I don=E2=80=99t think so. I think it=E2=80=99s very reasonable t= hat you accept >> bitmap-mode=3Dconditional for sync=3Dincremental.) >> >=20 > Right, I left this a secret wiggle room. If you specify the correct > bitmap sync mode for the incremental sugar, it will actually let it > slide. If you specify the wrong one, it will error out. >=20 > However, I think this is perfectly correct advice from the API: Please > use this mode with sync=3Dbitmap and do not use it otherwise. >=20 > Would you like me to change it to be more technically correct and > document the little affordance I made? It=E2=80=99s probably better not to. Better forbid as much as we can so = that we can break compatibility to users that happened to use it still =E2=80=9Cb= ecause it works=E2=80=9D. Max --vgwFx0mYKSYUk9DlnyMB5IfQRvE4qpT6d-- --ttXvptYEExBvOeKWOJV27ICUiQW0KDkUU Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl0L1H8ACgkQ9AfbAGHV z0AYSAf/RsqrKuU0YlD9e2KI1Z8Eq3tQY3T09E4rJZGnuVr2Pb2NIdDsfDRt/Jk3 Dii8VJe9n9GsrJsTKM9g4xpI4E9fQ5ymCZtKOtPI7Ma+XYHox6BqMSKVvScwIEri 5m42r1vdTal0hDPOap07rH7GrWLdSxEFQZ3DxuBy6asO1pxZJH9wYK7CN6HI6ZOI gz6QvdbRLdn9enrZ6xUDtticDOlUDCbDO9qw0SHsPC+fzblpWVUHlO8GwNTfXvwp 4hNVTgEZygC3yqDh2sXDdNA3Ga8wHSrcsiDAVFdyYWTCkMub/+PmaMYvzKznNSJM uycR1f4IGHsIL+ylC/0q0xIj/0euLQ== =orx7 -----END PGP SIGNATURE----- --ttXvptYEExBvOeKWOJV27ICUiQW0KDkUU--