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spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:50154 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hdzmr-0003RQ-6w for qemu-devel@archiver.kernel.org; Thu, 20 Jun 2019 12:19:45 -0400 Received: from eggs.gnu.org ([209.51.188.92]:36542) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hdzkc-000299-Ta for qemu-devel@nongnu.org; Thu, 20 Jun 2019 12:17:27 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hdzfU-0008PY-IA for qemu-devel@nongnu.org; Thu, 20 Jun 2019 12:12:10 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53382) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hdzfS-0008MW-CN; Thu, 20 Jun 2019 12:12:06 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 8F0142F8BD7; Thu, 20 Jun 2019 16:11:57 +0000 (UTC) Received: from [10.10.123.29] (ovpn-123-29.rdu2.redhat.com [10.10.123.29]) by smtp.corp.redhat.com (Postfix) with ESMTP id 18A7E5C221; Thu, 20 Jun 2019 16:11:50 +0000 (UTC) To: Max Reitz , qemu-devel@nongnu.org, qemu-block@nongnu.org References: <20190620010356.19164-1-jsnow@redhat.com> <20190620010356.19164-4-jsnow@redhat.com> From: John Snow Openpgp: preference=signencrypt Autocrypt: addr=jsnow@redhat.com; prefer-encrypt=mutual; keydata= mQINBFTKefwBEAChvwqYC6saTzawbih87LqBYq0d5A8jXYXaiFMV/EvMSDqqY4EY6whXliNO IYzhgrPEe7ZmPxbCSe4iMykjhwMh5byIHDoPGDU+FsQty2KXuoxto+ZdrP9gymAgmyqdk3aV vzzmCa3cOppcqKvA0Kqr10UeX/z4OMVV390V+DVWUvzXpda45/Sxup57pk+hyY52wxxjIqef rj8u5BN93s5uCVTus0oiVA6W+iXYzTvVDStMFVqnTxSxlpZoH5RGKvmoWV3uutByQyBPHW2U 1Y6n6iEZ9MlP3hcDqlo0S8jeP03HaD4gOqCuqLceWF5+2WyHzNfylpNMFVi+Hp0H/nSDtCvQ 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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" On 6/20/19 11:25 AM, Max Reitz wrote: > On 20.06.19 03:03, John Snow wrote: >> This adds a "never" policy for bitmap synchronization. Regardless of i= f >> the job succeeds or fails, we never update the bitmap. This can be use= d >> to perform differential backups, or simply to avoid the job modifying = a >> bitmap. >> >> Signed-off-by: John Snow >> --- >> qapi/block-core.json | 6 +++++- >> block/backup.c | 5 +++-- >> 2 files changed, 8 insertions(+), 3 deletions(-) >> >> diff --git a/qapi/block-core.json b/qapi/block-core.json >> index 6d05ad8f47..0332dcaabc 100644 >> --- a/qapi/block-core.json >> +++ b/qapi/block-core.json >> @@ -1146,10 +1146,14 @@ >> # @conditional: The bitmap is only synchronized when the operation is= successul. >> # This is useful for Incremental semantics. >> # >> +# @never: The bitmap is never synchronized with the operation, and is >> +# treated solely as a manifest of blocks to copy. >> +# This is useful for Differential semantics. >> +# >=20 > Again, this is too buzzword-y for my taste. I don=E2=80=99t find it as= bad > because there is not much to explain about this mode, and you do explai= n > it above, but still. >=20 Explained in my response to patch 2, I disagree. > Like, I (me myself) read this and after the first sentence I think I=E2= =80=99ve > understood what this is. Then I read =E2=80=9Cfor Differential semanti= cs=E2=80=9D and > I=E2=80=99m confused. After a couple of seconds, I realize what you me= an > because I=E2=80=99ve described in my response to patch 1. >=20 > One reason it leaves the buzzword-y taste is because =E2=80=9Cdifferent= ial=E2=80=9D is > never explained anywhere. bitmaps.rst makes two mentions of it, but it > too just assumes I know what you mean. Also, incremental backups are > just a certain kind of differential backups. >=20 This, however, is a real shortcoming of the doc. You'll notice I didn't propose a doc update in this patchset, because secretly it's an RFC and I did expect a v2+. > So you need to explain =E2=80=9Cdifferential=E2=80=9D somewhere and how= it differs from > =E2=80=9Cincremental=E2=80=9D in this regard. Why not here? >=20 Too broad of a concept to explain down in qapi comment strings, or I'd have to explain it everywhere. bitmaps.rst is the correct place. > =E2=80=9CThis is useful when you wish to repeatedly perform operations = in > reference to a constant synchronization point (when the bitmap was > created).=E2=80=9D >=20 > Or something. >=20 > Max >=20 >> # Since: 4.1 >> ## >> { 'enum': 'BitmapSyncMode', >> - 'data': ['conditional'] } >> + 'data': ['conditional', 'never'] } >> =20 >> ## >> # @MirrorCopyMode: >=20