Re: Use genimage for disk-image creation.

["Ludovic Courtès" <ludo@gnu.org>]

Hi Mathieu!

Mathieu Othacehe <m.othacehe@gmail.com> skribis:

> Let say I want to create a disk-image with one ext4 partition starting
> at offset 10M. I can write the following genimage config file:
>
> image system {
> 	hdimage {}
>
> 	partition rootfs {
> 		partition-type = 0x83
> 		image = "rootfs.ext4"
> 		size = 8G
> 		offset = 10M
> 	}
> }
>
> image rootfs.ext4 {
>         name = "rootfs"
>         ext4 {
>                 label = "rootfs"
> 		use-mke2fs = true
>         }
>         size = 8G
>         mountpoint = "/"
> }
>
>
> and run the command:
>
> fakeroot genimage --config ~/tmp/genimage.cfg --rootpath=/home/mathieu/image-root/
>
> where image-root is a directory containing the result of a `guix system
> init`. The directory size is about 6GiB.
>
> It takes 8 minutes to generate this disk-image, versus 2h30 using `guix
> system disk-image`.
>
> I'm aware that this might not be a fair comparison but, I think its
> already significant.
>
> Danny, Ludo, WDYT? Could we modify "system-disk-image" to use genimage
> as a backend instead of spawning a VM?

I’m completely sold to the idea.  :-)

Apparently ‘genimage’ supports many file systems, including ext[234] and
ISO9660, which are the two formats we support via ‘--file-system-type’.
It does not support Btrfs, but ‘guix system disk-image’ doesn’t support
it either so far.

Looking at ‘image-ext2.c’ reveals that genimage actually just shells out
to mke2fs.  Indeed, I discovered that ‘mke2fs -d /my/root’ copies
/my/root as the image’s root directory.  Likewise, for ISO, it just
shells out to ‘genisoimage’.

So I think that we could avoid ‘genimage’ altogether and implement
similar functionality for ext4/ISO in (gnu build disk-image).

WDYT?

Thanks,
Ludo’.