From: John Snow <jsnow@redhat.com>
To: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>,
qemu-devel@nongnu.org
Cc: famz@redhat.com, den@virtuozzo.com,
Stefan Hajnoczi <stefanha@redhat.com>
Subject: Re: [Qemu-devel] [PATCH RFC] external backup api
Date: Fri, 5 Feb 2016 14:48:16 -0500 [thread overview]
Message-ID: <56B4FC80.1070402@redhat.com> (raw)
In-Reply-To: <1453482459-80179-1-git-send-email-vsementsov@virtuozzo.com>
On 01/22/2016 12:07 PM, Vladimir Sementsov-Ogievskiy wrote:
> Hi all.
>
> This is the early begin of the series which aims to add external backup
> api. This is needed to allow backup software use our dirty bitmaps.
>
> Vmware and Parallels Cloud Server have this feature.
>
Have a link to the equivalent feature that VMWare exposes? (Or Parallels
Cloud Server) ... I'm curious about what the API there looks like.
> There is only one patch here, about querying dirty bitmap from qemu by
> qmp command. It is just an updated and clipped (hmp command removed) old
> my patch "[PATCH RFC v3 01/14] qmp: add query-block-dirty-bitmap".
>
> Before writing the whole thing I'd like to discuss the details. Or, may
> be there are existing plans on this topic, or may be someone already
> works on it?
>
> I see it like this:
>
> =====
>
> - add qmp commands for dirty-bitmap functions: create_successor, abdicate,
> reclaime.
Hm, why do we need such low-level control over splitting and merging
bitmaps from an external client?
> - make create-successor command transaction-able
> - add query-block-dirty-bitmap qmp command
>
> then, external backup:
>
> qmp transaction {
> external-snapshot
> bitmap-create-successor
> }
>
> qmp query frozen bitmap, not acquiring aio context.
>
> do external backup, using snapshot and bitmap
>
> if (success backup)
> qmp bitmap-abdicate
> else
> qmp bitmap-reclaime
>
> qmp merge snapshot
> =====
>
Hm, I see -- so you're hoping to manage the backup *entirely*
externally, so you want to be able to reach inside of QEMU and control
some status conditions to guarantee it'll be safe.
I'm not convinced QEMU can guarantee such things -- due to various flush
properties, race conditions on write, etc. QEMU handles all of this
internally in a non-public way at the moment.
>
> In the following patch query-bitmap acquires aio context. This must be
> ofcourse dropped for frozen bitmap.
> But to make it in true way, I think, I should check somehow that this is
> not just frozen bitmap, but the bitmap frozen by qmp command, to avoid
> incorrect quering of bitmap frozen by internal backup (or other
> mechanizm).. May be, it is not necessary.
>
>
>
next prev parent reply other threads:[~2016-02-05 19:48 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-22 17:07 [Qemu-devel] [PATCH RFC] external backup api Vladimir Sementsov-Ogievskiy
2016-01-22 17:07 ` [Qemu-devel] [PATCH] qmp: add query-block-dirty-bitmap Vladimir Sementsov-Ogievskiy
2016-01-22 17:22 ` Denis V. Lunev
2016-01-22 17:28 ` Vladimir Sementsov-Ogievskiy
2016-01-22 18:28 ` Denis V. Lunev
2016-01-22 18:43 ` Eric Blake
2016-02-05 19:48 ` John Snow [this message]
2016-02-06 9:19 ` [Qemu-devel] [PATCH RFC] external backup api Vladimir Sementsov-Ogievskiy
2016-02-08 21:14 ` John Snow
2016-02-09 15:54 ` Vladimir Sementsov-Ogievskiy
2016-02-09 16:51 ` John Snow
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