linux-ext4 - Re: [PARCH 0/1 RFC] e2image: Add support for QCOW2 image format

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Date:	Wed, 1 Dec 2010 21:16:52 +0200
From:	Amir Goldstein <amir73il@...il.com>
To:	Lukas Czerner <lczerner@...hat.com>
Cc:	tytso@....edu, adilger@...ger.ca, sandeen@...hat.com,
	linux-ext4@...r.kernel.org
Subject: Re: [PARCH 0/1 RFC] e2image: Add support for QCOW2 image format

On Wed, Dec 1, 2010 at 7:41 PM, Lukas Czerner <lczerner@...hat.com> wrote:
> Hi, all
>
> As Ted suggested on LPC I started to play with e2image to add support for
> exporting images in QCOW2 format (http://en.wikipedia.org/wiki/Qcow2). The
> advantage of this format is mainly that the resulting image is quite small
> (because we write only the metadata blocks) and it is not sparse unlike
> "sparse" image format.
>
> I am presenting you an initial parch, which works for me quite nicely, however
> so far it did received just limited testing. Nevertheless you can try it simply
> by invoking e2image with '-q' parameter like this:
>
>        e2image -q /dev/sda1 myimage
>
> or you can add '-s' option so the file names are scrambled. To mount that qcow2
> image I usually use 'qemu-nbd':
>
>        modprobe nbd max_part=8
>        qemu-nbd --connect=/dev/nbd0 myimage
>        mount -o ro /dev/nbd0 /mnt/test/
>
> However I have experienced some problems with qemu-nbd from time to time. Also
> for some reason, when you mount the image read-write, you'll destroy it. So far
> I was not able to figure out why (I did not tried at all to be honest), it may
> be problem in my image format or even in qemu itself, so if you have any idea,
> please let me know.
>
> QCOW2 format supports other neat features like compression, encryption and
> snapshots. None of those feature are supported in this patch and the question
> is, do we need it ? I can imagine for example snapshots to be useful for
> roll-back changes made by e2fsck, but this is hardly problem of e2image itself.
>
> So, please look at the patch, try it and let me know what else you thing is
> useful to implement, or what would you like to change.
>

Hi Lukas,

This is very cool :-)
My wish is to export next3/ext4 snapshots as qcow2 snapshots.
I actually thought of implementing e2image -x <snapid> as a way to
export a snapshot image,
but using qcow2, file system can be exported with all of it's snapshots.
It should be quite trivial since next3 snapshots contain a map of changed blocks
and I suppose qcow2 snapshots should be the same.
Now I only need to find the time to do it...

Amir.


> Anny comments appreciated.
>
> Thanks!
>
> -Lukas
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