[arch-releng] [archiso] saying good-bye to union-fs-method?

Gerardo Exequiel Pozzi vmlinuz386 at yahoo.com.ar
Tue May 31 11:08:52 EDT 2011

On 05/31/2011 07:54 AM, Thomas Bächler wrote:
> Am 31.05.2011 03:21, schrieb Gerardo Exequiel Pozzi:
>> Hi
>> * With 2.6.39 there is no aufs2 support, at least for a long time[#1].
>> * I think that back in time with unionfs is not desirable, needs a
>> complete kernel patch.
>> * union-fs-fuse does not work good.
>> What about using the method like in Fedora? (basically a device-mapper
>> with a snapshot in tmpfs).
>> This change from file-to-file level to block-to-block logic.
> This actually sounds pretty cool. However, I don't understand how it
> works: The squashfs file system is a read-only one, how can we put that
> into a block-level snapshot?
Yes, but there are at least one downside: since is not an union-fs, 
there is no concept of layers. We are currently using "overlay" thats 
overlap some files on the layer "root-image". With the others layers 
like "core-pkgs" and "lib-modules", there are no overlap and can be 
replaced by a simple mount point.
Of course this "overlay" can be merged at build time on "root-image".

About your question: The squasfs image contains only one file... an 
image of and 4 GiB ext4. There is another small squasfs image with 
another one file inside that is a "lvm snapshot". So dm device is made 
via these images loopback mounted...

The code is here 

Gerardo Exequiel Pozzi
\cos^2\alpha + \sin^2\alpha = 1

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