[Sugar-devel] Documenting the SoaS file system

[Sebastian Dziallas]

Luke Faraone wrote:
> On Wed, Jul 29, 2009 at 08:32, Caroline Meeks
> <caroline at solutiongrove.com <mailto:caroline at solutiongrove.com>> wrote:
>
>     When I read about squashfs in wikipedia or chat with friends about
>     it, its decribed as read-only and optimized for space.  If we are
>     rewritting our squashfs everytime the user saves data, that could be
>     the source of a lot of our failures.  If we never rewrite it, then
>     probably its a red harring and we need to look elsewhere.
>
>
>  From what I understand, the squashfs is *never* rewritten once created.
> All changes are stored in a "LVM Snapshot", which is just another file
> on the underlying FAT filesystem.

As far as I know, what happens is this:

* At build time, all packages are installed (and so is the base system) 
and end up in an image, which gets compressed using squashfs.

* Once you boot your disk / device, any change you make gets saved into 
this spurious file (either for the overlay or home), which contains only 
the changes made since you booted for the first time. Those changes get 
- again afaik - mapped with some magic (don't ask me how, maybe some 
Fedora folks or the wiki know) on the fly into the usual filesystem.

--Sebastian