Union mounts and package maintenance (Blue sky)
Russell Coker <russell@coker.com.au> writes:
> On Sun, 15 Jul 2001 11:05, Tommi Virtanen wrote:
> > You are missing the point of union mounts.
> > Storing "general tools and maintenance stuff" separately
> > from "applications", and activating them in order, is
> > orthogonal from names used to refer to them.
>
> So we have two filesystems mounted on the root directory, one for basic stuff
> needed for booting and one for the rest.
>
> Then what happens when I create a package that has some files needed for
> booting and some files not needed for booting (similar to having some files
> in /usr/bin and some in /sbin now). How do I specify which of the two file
> systems my files are to go in?
Well, AFAIK, there are a few schools of thought.
The one that seems simple and manageable to me is to do
something very much like stow, and make packages install in
e.g. /package/$NAME/{bin,man,...}, and union mount
/package/*/bin to /bin. I'm not sure if this will apply nicely
to the _real_ core of the OS, but then again that tends to be
in the "needed for booting" part.
The other one is that the / union mount is made such that any
writes to /bin go to the "rest" filesystem, and the parts
required for booting can be updated with other means. (E.g.
mounting that filesystem elsewhere and copying things from /
specifically to that filesystem.)
Anyone have any pointers to real papers on these? I can't find
any in the Plan 9 papers, and I don't see anything really
relevant in the tidbits about the Hurd I can find.. Surely
some research OS like Spring has touched that area already.
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