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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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