From: Stefan Hajnoczi <stefanha@redhat.com>
To: John Snow <jsnow@redhat.com>
Cc: kwolf@redhat.com,
Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>,
qemu-devel@nongnu.org,
Vladimir Sementsov-Ogievskiy <vsementsov@parallels.com>,
den@openvz.org, pbonzini@redhat.com
Subject: Re: [Qemu-devel] [PATCH 2/8] qcow2: add dirty-bitmaps feature
Date: Wed, 24 Jun 2015 10:39:03 +0100 [thread overview]
Message-ID: <20150624093903.GB7454@stefanha-thinkpad.redhat.com> (raw)
In-Reply-To: <55899E23.6080707@redhat.com>
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On Tue, Jun 23, 2015 at 01:57:55PM -0400, John Snow wrote:
> On 06/15/2015 10:42 AM, Stefan Hajnoczi wrote:
> > On Fri, Jun 12, 2015 at 03:02:33PM -0400, John Snow wrote:
> >>
> >>
> >> On 06/10/2015 10:30 AM, Stefan Hajnoczi wrote:
> >>> On Mon, Jun 08, 2015 at 06:21:20PM +0300, Vladimir Sementsov-Ogievskiy wrote:
> >>>
> >>> I noticed a corner case, it's probably not a problem in practice:
> >>>
> >>> Since the dirty bitmap is stored with the help of a BlockDriverState
> >>> (and its bs->file), it's possible that writing the bitmap will cause
> >>> bits in the bitmap to be dirtied!
> >>>
> >>
> >> But since it's metadata and not stored within a disk sector, can this
> >> actually happen? Do you have an example of a scenario where this might
> >> come up?
> >
> > The persistent dirty bitmap for bs->file is storeed in the qcow2 BDS.
> > This results in recursion.
> >
> > This is a misconfiguration but I just want to understand what happens
> > when someone does this by mistake.
> >
> > Stefan
> >
>
> I still don't follow you, actually.
>
> The dirty bitmap only tracks changed virtual disk sectors, not actual
> file sectors, right? Writing a bitmap that describes foo.qcow2 to
> foo.qcow2 won't dirty bitmaps, it's an out-of-channel write as far as
> the bitmap is concerned.
>
> Right? Am I fatally misunderstanding the situation?
There is no out-of-channel for bs->file. The bs->file raw-posix image
file includes the bs qcow2 sectors that hold the dirty bitmap.
This is a corner case and I don't think any valid configuration would
hit it.
Stefan
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next prev parent reply other threads:[~2015-06-24 9:39 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-08 15:21 [Qemu-devel] [PATCH v2 RFC 0/8] block: persistent dirty bitmaps Vladimir Sementsov-Ogievskiy
2015-06-08 15:21 ` [Qemu-devel] [PATCH 1/8] spec: add qcow2-dirty-bitmaps specification Vladimir Sementsov-Ogievskiy
2015-06-09 16:01 ` John Snow
2015-06-09 17:03 ` Stefan Hajnoczi
2015-06-10 8:19 ` Vladimir Sementsov-Ogievskiy
2015-06-10 8:49 ` Vladimir Sementsov-Ogievskiy
2015-06-10 13:00 ` Eric Blake
2015-06-11 10:16 ` Vladimir Sementsov-Ogievskiy
2015-06-10 13:24 ` Stefan Hajnoczi
2015-06-11 10:19 ` Vladimir Sementsov-Ogievskiy
2015-06-11 13:03 ` Stefan Hajnoczi
2015-06-11 16:21 ` John Snow
2015-06-12 10:28 ` Stefan Hajnoczi
2015-06-12 15:19 ` John Snow
2015-06-10 15:34 ` Kevin Wolf
2015-06-11 10:25 ` Vladimir Sementsov-Ogievskiy
2015-06-11 16:30 ` John Snow
2015-06-12 8:33 ` Kevin Wolf
2015-08-24 10:46 ` Vladimir Sementsov-Ogievskiy
2015-08-24 13:30 ` Vladimir Sementsov-Ogievskiy
2015-08-24 14:08 ` Vladimir Sementsov-Ogievskiy
2015-08-24 14:04 ` Vladimir Sementsov-Ogievskiy
2015-08-31 22:21 ` Eric Blake
2015-08-31 22:24 ` John Snow
2015-06-08 15:21 ` [Qemu-devel] [PATCH 2/8] qcow2: add dirty-bitmaps feature Vladimir Sementsov-Ogievskiy
2015-06-09 16:52 ` Stefan Hajnoczi
2015-06-10 14:30 ` Stefan Hajnoczi
2015-06-12 19:02 ` John Snow
2015-06-15 14:42 ` Stefan Hajnoczi
2015-06-23 17:57 ` John Snow
2015-06-24 9:39 ` Stefan Hajnoczi [this message]
2015-08-14 17:14 ` Vladimir Sementsov-Ogievskiy
2015-08-26 9:09 ` Stefan Hajnoczi
2015-06-11 23:04 ` John Snow
2015-06-15 14:05 ` Vladimir Sementsov-Ogievskiy
2015-06-15 16:53 ` John Snow
2015-06-12 21:55 ` John Snow
2015-08-26 13:15 ` Vladimir Sementsov-Ogievskiy
2015-08-26 14:14 ` Vladimir Sementsov-Ogievskiy
2015-08-27 12:43 ` Vladimir Sementsov-Ogievskiy
2015-06-08 15:21 ` [Qemu-devel] [PATCH 3/8] block: store persistent dirty bitmaps Vladimir Sementsov-Ogievskiy
2015-06-08 15:21 ` [Qemu-devel] [PATCH 4/8] block: add bdrv_load_dirty_bitmap Vladimir Sementsov-Ogievskiy
2015-06-09 16:01 ` Stefan Hajnoczi
2015-06-10 22:33 ` John Snow
2015-06-11 10:41 ` Vladimir Sementsov-Ogievskiy
2015-06-08 15:21 ` [Qemu-devel] [PATCH 5/8] qcow2: add qcow2_dirty_bitmap_delete_all Vladimir Sementsov-Ogievskiy
2015-06-08 15:21 ` [Qemu-devel] [PATCH 6/8] qcow2: add autoclear bit for dirty bitmaps Vladimir Sementsov-Ogievskiy
2015-06-09 15:49 ` Stefan Hajnoczi
2015-06-09 15:50 ` Stefan Hajnoczi
2015-08-27 7:45 ` Vladimir Sementsov-Ogievskiy
2015-08-31 11:06 ` Vladimir Sementsov-Ogievskiy
2015-08-31 22:39 ` Eric Blake
2015-08-31 22:50 ` Eric Blake
2015-06-10 23:42 ` John Snow
2015-06-11 8:35 ` Kevin Wolf
2015-06-11 10:49 ` Vladimir Sementsov-Ogievskiy
2015-06-11 16:36 ` John Snow
2015-06-08 15:21 ` [Qemu-devel] [PATCH 7/8] qemu: command line option " Vladimir Sementsov-Ogievskiy
2015-06-11 20:57 ` John Snow
2015-06-12 21:49 ` John Snow
2015-06-08 15:21 ` [Qemu-devel] [PATCH 8/8] iotests: test internal persistent dirty bitmap Vladimir Sementsov-Ogievskiy
2015-06-09 16:17 ` Eric Blake
2015-06-10 15:27 ` [Qemu-devel] [PATCH v2 RFC 0/8] block: persistent dirty bitmaps Stefan Hajnoczi
2015-06-11 11:22 ` Vladimir Sementsov-Ogievskiy
2015-06-11 13:14 ` Stefan Hajnoczi
2015-06-11 20:06 ` Stefan Hajnoczi
2015-06-12 9:58 ` Denis V. Lunev
2015-06-12 10:36 ` Stefan Hajnoczi
2015-08-26 6:26 ` Vladimir Sementsov-Ogievskiy
2015-08-26 9:13 ` Stefan Hajnoczi
2015-06-12 19:34 ` John Snow
2015-06-17 14:29 ` Vladimir Sementsov-Ogievskiy
2015-06-24 0:21 ` John Snow
2015-07-08 12:24 ` Vladimir Sementsov-Ogievskiy
2015-07-08 15:21 ` John Snow
2015-08-27 10:08 ` Vladimir Sementsov-Ogievskiy
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