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UID/GID Management

I'm not very clear about how UID management works in Inferno.

Once an application calls `auth()' with `setid' non-zero, the manual
claims that the UID of the remote party is written to /dev/user, (which
presumably changes the process uid?).

This UID is used for subsequent `Tattach'es and for file access 
comparisions.  How do I prevent a device logging in with a false ID?

To put the question in  another way: 

I would like an electric meter in my house to be readable from the
utility company.  So I have my meter export `/dev/meter' and mount it
onto my firewall at `/export/meters/power'.  Now I'd like only the
utility co.  to read the meter, so I assign u+rwx,o-rwx,g-rwx
permissions to the file.

Now how do I ensure that the utility co.  authenticates to the firewall
with the correct UID?  Does the electricity meter need to know the UID
that the utility co.  needs to use?

<koshy@india.hp.com>			My Personal Opinions Only