[Devel] Re: [PATCH] c/r: Add UTS support (v4)

[Dave Hansen]

On Fri, 2009-03-20 at 17:26 -0400, Oren Laadan wrote:
> Dave Hansen wrote:
> > On Fri, 2009-03-20 at 16:48 -0400, Oren Laadan wrote:
> >> Does that scale well with many (1000's) of tasks ?
> >>
> >> (The motivation to expose 'nsproxy_objref' to user space was to allow
> >> user-space to decide on a sequence of clones/unshared that will create
> >> an equivalent process tree with space-efficient nsproxy's).
> > 
> > OK, so you're saying that there's no way for userspace to tell that a
> > set of tasks share an nsproxy other than exporting that nsproxy?
> 
> I don't think so. Maybe the namespaces people know better.

Please go look at the code.

Two processes share an nsproxy (or *can* share an nsproxy) when all of
the namespace pointers are the same.  After allocation and
initialization, we basically don't ever write to the nsproxy.  We just
hook it into a task and run with it.

If anything ever unshares one of the nsproxy namespaces, before writing
to it we *first* create a new nsproxy which is a copy of the old one.

We basically open-code copy-on-write semantics for the nsproxy.

This means that it is safe for any two tasks that share all of the
pointers in the nsproxy to share an nsproxy itself.

-- Dave

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