Hi,
[...]
> We would like to participate in Google Summer code.
> This particular profile matches with the project (Universal PackageIf it's part of your curriculum, you can't do it as SoC project I think.
> Manager) we are doing here as part of our curriculum.
Independent of SoC however, we would like to learn more about this UPM project, and how it is related to the GNU system or the Hurd...
In UNIX systems, traditionally most software is installed in a common directory hierachy, where files from various packages live beside each other, grouped by function: User-invokable executables in /bin, configuration files in /etc, architecture specific static files in /lib, variable data in /var and so on. To allow clean installation, deinstallation, and upgrade of software packages, GNU/Linux distributions usually come with a package manager, which keeps track of all files upon installation/removal in some kind of central database.
An alternative approach is the one implemented by GNU Stow: Each package is actually installed in a private directory tree. The actual standard directory structure is then created by collecting the individual files from all the packages, and presenting them in the common /bin, /lib etc. locations.
While the normal Stow package (for traditional UNIX systems) uses symlinks to the actual files, updated on installation/deinstallation events, the Hurd translator mechanism allows a much more elegant solution: Stowfs (which is actually a special mode of unionfs) creates virtual directories on the fly, composed of all the files from the individual package directories.
The problem with this approach is that unionfs presently can be launched only once the system is booted up, meaning the virtual directories are not available at boot time. But the boot process itself already needs access to files from various packages. So to make this design actually usable, it is necessary to come up with a way to launch unionfs very early at boot time, along with the root filesystem.
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-antrik-
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