Re: [9fans] How to implement a moral equivalent of automounter in Plan9?

["Russ Cox" <rsc@swtch.com>]

> a couple of questions come to mind.  how does writing
> to a ns interact with shared namespaces?  does it automaticly
> fork the namespace?  seems iffy.  which leads to the next
> obvious question
>
> how do you prevent a race between changing the namespace and
> opening fds?
>
> and, what about open file descriptors?
>
> seems like a big can of worms.

None of these questions are any different in this
context than if there was simply some other process
sharing the name space and doing the same manipulations.

A writable #p/pid/ns seems strange to me
(not nearly as natural as Roman suggested),
but maybe it would be fine.  No one has cared
enough to explore it.

I don't think a writable #p/pid/ns would really
help you write an automounter.  You don't know
the pid you are getting the 9P request from
(maybe it is on another machine!).

If I had to write an automounter like you describe
and I was going to tweak the kernel to make it
easier, I would change name spaces to be hierarchical,
so that rfork(RFNAMEG) (or perhaps some new bit)
insulates the parent from the child's modifications
but not vice versa.  Then the automounter can sit
in some early name space and mount things, and all
the name spaces that were forked off would see them.
That is easier to reason about than writing #p/pid/ns.

Russ