From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
To: Nikolay Shirokovskiy <nshirokovskiy@virtuozzo.com>,
qemu-devel@nongnu.org, qemu block <qemu-block@nongnu.org>
Cc: Denis Lunev <den@virtuozzo.com>,
Maxim Nestratov <mnestratov@virtuozzo.com>,
John Snow <jsnow@redhat.com>, Eric Blake <eblake@redhat.com>,
Fam Zheng <famz@redhat.com>
Subject: Re: [Qemu-devel] [RFC] dirty bitmap state uncertainty under certain conditions
Date: Tue, 22 Nov 2016 15:34:02 +0300 [thread overview]
Message-ID: <9f94317f-a5c7-1fe5-8c6e-cc7336477ed0@virtuozzo.com> (raw)
In-Reply-To: <2fb12281-1023-71c0-7fd9-39e27787c1e9@virtuozzo.com>
22.11.2016 15:01, Nikolay Shirokovskiy wrote:
> Hi, everyone.
>
> There is a problem with current incremental backups. Imagine I ask qemu to
> make an incremental backup then go away and return back when backup
> job is finished. Qemu process dismisses the job completely and I missed
> all the events so I don't know the result of the operation and what is
> most important I don't know the base for dirty bitmap now. In case of failure
> it is previous backup and in case of success it is the last backup. Qemu does
> not track dirty bitmap base for me so I have no choice other then clear
> dirty bitmap and make full backup which would be rather unexpected from user
> POV (The situation of going away/coming back is libvirt crash/restart of course.)
>
> I guess problem has wider scope. In case I miss successfull completion of full
> backup my only option is to drop backup file and redo the backup completely
> which is rather wasteful. AFAIU I can not query backup completion result from
> backup file itself. I guess there can be similar issues for other qemu jobs.
>
> Nikolay
I suggest an additional int field for BdrvDirtyBitmap, which will count
number of bdrv_dirty_bitmap_abdicate() calls and will be available to
the user through qmp query-block. So, for the user, <counter
incremented> <=> <backup was successful and bitmap updated>.
--
Best regards,
Vladimir
next parent reply other threads:[~2016-11-22 12:34 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <2fb12281-1023-71c0-7fd9-39e27787c1e9@virtuozzo.com>
2016-11-22 12:34 ` Vladimir Sementsov-Ogievskiy [this message]
2016-11-22 13:38 ` [Qemu-devel] [RFC] dirty bitmap state uncertainty under certain conditions Nikolay Shirokovskiy
2016-11-22 16:07 ` John Snow
2016-11-22 16:16 ` Vladimir Sementsov-Ogievskiy
2016-11-22 16:16 ` Eric Blake
2016-11-22 17:26 ` John Snow
2016-11-23 9:40 ` Stefan Hajnoczi
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