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Re: [Qemu-devel] Persistent bitmaps for non-qcow2 formats
From: |
Max Reitz |
Subject: |
Re: [Qemu-devel] Persistent bitmaps for non-qcow2 formats |
Date: |
Wed, 23 Aug 2017 19:31:56 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 |
On 2017-08-22 21:07, John Snow wrote:
[...]
> (3) Add either a new flag that turns qcow2's backing file into a full
> R/W backing file, or add a new extension to qcow2 entirely (bypassing
> the traditional backing file mechanism to avoid confusion for older
> tooling) that adds a new read-write backing file field.
>
> This RW backing file field will be used for all reads AND writes; the
> qcow2 in question becomes a metadata container on top of the BDS chain.
> We can re-use Vladimir's bitmap persistence extension to save bitmaps in
> a qcow2 shell.
>
> The qcow2 becomes effectively a metadata cache for a new (essentially)
> filter node that handles features such as bitmaps. This could also be
> used to provide allocation map data for RAW files and other goodies down
> the road.
>
> Hopefully this achieves our desire to not create new formats AND our
> desire to concentrate features (and debugging, testing, etc) into qcow2,
> while allowing users to "have bitmaps with raw files."
>
> Of course, in this scenario, users now have two files: a qcow2 wrapper
> and the actual raw file in question; but regardless of how we were going
> to solve this, a raw file necessitates an external file of some sort,
> else we give up the idea that it was a raw file.
>
>
> Sound good?
While I don't quite like the idea of R/W backing files, I guess "don't
quite like" is still rather good.
I like how this idea would allow us to use the existing code without
putting just arbitrary binary data into the qcow2 file; the data still
relates to the virtual disk represented by the qcow2 image.
So design-wise, I don't think I have any complaints.
As for Kevin, he's on PTO, though. ;-)
Max
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- Re: [Qemu-devel] Persistent bitmaps for non-qcow2 formats, (continued)
- Re: [Qemu-devel] Persistent bitmaps for non-qcow2 formats, John Snow, 2017/08/28
- Re: [Qemu-devel] Persistent bitmaps for non-qcow2 formats, Yaniv Lavi (Dary), 2017/08/29
- Re: [Qemu-devel] Persistent bitmaps for non-qcow2 formats, Max Reitz, 2017/08/30
- Re: [Qemu-devel] Persistent bitmaps for non-qcow2 formats, Yaniv Lavi (Dary), 2017/08/30
- Re: [Qemu-devel] Persistent bitmaps for non-qcow2 formats, John Snow, 2017/08/30
- Re: [Qemu-devel] Persistent bitmaps for non-qcow2 formats, John Snow, 2017/08/28
- Re: [Qemu-devel] Persistent bitmaps for non-qcow2 formats, Eric Blake, 2017/08/29
- Re: [Qemu-devel] Persistent bitmaps for non-qcow2 formats, John Snow, 2017/08/29
- Re: [Qemu-devel] Persistent bitmaps for non-qcow2 formats, Max Reitz, 2017/08/30
- Re: [Qemu-devel] Persistent bitmaps for non-qcow2 formats, Max Reitz, 2017/08/30
Re: [Qemu-devel] Persistent bitmaps for non-qcow2 formats,
Max Reitz <=
Re: [Qemu-devel] [Qemu-block] Persistent bitmaps for non-qcow2 formats, Stefan Hajnoczi, 2017/08/30