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Re: [Qemu-devel] Closing Bitmaps (Was: Re: [PATCH v7 03/24] block: Relea
From: |
Fam Zheng |
Subject: |
Re: [Qemu-devel] Closing Bitmaps (Was: Re: [PATCH v7 03/24] block: Release dirty bitmaps in bdrv_close()) |
Date: |
Wed, 18 Nov 2015 10:29:41 +0800 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Tue, 11/17 12:05, John Snow wrote:
> Still the subject of debate on-list, but the thought is roughly this:
Thanks for summerizing this!
>
> Bitmaps will be able to flush-to-file on close. (If they have no
> persistence data, it's a no-op (maybe.)) This might mean being flushed
> to their own BDS -- the one they are describing -- as a qcow2 extension.
> Or, it could be to an arbitrary new standalone file format designed for
> the sole purpose of containing bitmap data.
>
> The discussion hasn't progressed beyond "Max and Kevin do not think
> storing arbitrary bitmaps in .qcow2 files is a good idea." The logical
> conclusion is "We need a new standalone format, then" but we haven't
> decided what that format will look like or how it will be used.
I second that. While storing dirty bitmap in the image itself sounds fine, it
is unlikely the best way for any other formats. Given that we will have a
standalone format for raw or other formats, it's probably not worth to extend
qcow2 specifically.
>
> Then, Through CLI arguments or QMP arguments, you can modify the
> persistence attributes of bitmaps -- choosing where to store them.
> Bitmaps for qcow2 nodes can be stored in their own node, bitmaps
> describing raw files will need to be stored in an external file.
>
> (Is it possible to create a block driver that doesn't implement
> read/write primitives, and only implements theoretical bitmap load/save
> primitives? We could create a block driver for a standalone bitmap
> container in this way...)
What about implementing it as a filter? It would work similar to blkdebug, with
.bdrv_co_writev to mark the in memory dirty bits (or even manage a
sophisticated cache to support large images efficiently), and .bdrv_close
to flush data to disk.
But that depends on the dynamic reconfigiration feature of block nodes, for
hot add/remove of dirty bitmap to work.
Fam
- [Qemu-devel] [PATCH v7 04/24] iotests: Rename filter_nbd to _filter_nbd in 083, (continued)
- [Qemu-devel] [PATCH v7 04/24] iotests: Rename filter_nbd to _filter_nbd in 083, Max Reitz, 2015/11/09
- [Qemu-devel] [PATCH v7 03/24] block: Release dirty bitmaps in bdrv_close(), Max Reitz, 2015/11/09
- Re: [Qemu-devel] [PATCH v7 03/24] block: Release dirty bitmaps in bdrv_close(), John Snow, 2015/11/11
- Re: [Qemu-devel] [PATCH v7 03/24] block: Release dirty bitmaps in bdrv_close(), Fam Zheng, 2015/11/12
- Re: [Qemu-devel] [PATCH v7 03/24] block: Release dirty bitmaps in bdrv_close(), John Snow, 2015/11/13
- Re: [Qemu-devel] [PATCH v7 03/24] block: Release dirty bitmaps in bdrv_close(), Fam Zheng, 2015/11/16
- Re: [Qemu-devel] [PATCH v7 03/24] block: Release dirty bitmaps in bdrv_close(), John Snow, 2015/11/16
- Re: [Qemu-devel] [PATCH v7 03/24] block: Release dirty bitmaps in bdrv_close(), Fam Zheng, 2015/11/16
- [Qemu-devel] Closing Bitmaps (Was: Re: [PATCH v7 03/24] block: Release dirty bitmaps in bdrv_close()), John Snow, 2015/11/17
- Re: [Qemu-devel] Closing Bitmaps (Was: Re: [PATCH v7 03/24] block: Release dirty bitmaps in bdrv_close()),
Fam Zheng <=
- Re: [Qemu-devel] Closing Bitmaps (Was: Re: [PATCH v7 03/24] block: Release dirty bitmaps in bdrv_close()), John Snow, 2015/11/18
- Re: [Qemu-devel] Closing Bitmaps (Was: Re: [PATCH v7 03/24] block: Release dirty bitmaps in bdrv_close()), Kevin Wolf, 2015/11/18
- Re: [Qemu-devel] Closing Bitmaps (Was: Re: [PATCH v7 03/24] block: Release dirty bitmaps in bdrv_close()), John Snow, 2015/11/18
[Qemu-devel] [PATCH v7 05/24] iotests: Change coding style of _filter_nbd in 083, Max Reitz, 2015/11/09
[Qemu-devel] [PATCH v7 06/24] iotests: Move _filter_nbd into common.filter, Max Reitz, 2015/11/09
[Qemu-devel] [PATCH v7 07/24] iotests: Make _filter_nbd drop log lines, Max Reitz, 2015/11/09
[Qemu-devel] [PATCH v7 08/24] iotests: Make _filter_nbd support more URL types, Max Reitz, 2015/11/09