From mboxrd@z Thu Jan  1 00:00:00 1970
Date: Wed, 15 Oct 2008 02:42:22 -0700
From: "Roman V. Shaposhnik" <rvs@sun.com>
In-reply-to: <26c1814ccfc8559a96987385a144c4e7@quanstro.net>
To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
Message-id: <1224063742.4463.145.camel@goose.sun.com>
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References: <26c1814ccfc8559a96987385a144c4e7@quanstro.net>
Subject: Re: [9fans] several things
Topicbox-Message-UUID: 1e724976-ead4-11e9-9d60-3106f5b1d025

On Mon, 2008-10-13 at 18:35 -0400, erik quanstrom wrote:
> > 4) What is the sense of
> > bind 'sth' 'the_same_sth'
> > ? (like 'bind / /' or 'bind /usr/ruda/a /usr/ruda/a')
>
> i believe this is a noop.  in the case of "bind / /", look
> at /lib/namespace.  consider the case where $rootdir
> isn't nil.

I have always thought, that the only reason for "bind <foo> <foo>"
is so that subsequent "bind -a/-b" would work:
   http://groups.google.com/group/comp.os.plan9/browse_thread/thread/c6cc9fb882978983/5067403b25124bac?hl=en&lnk=gst&q=bind+#5067403b25124bac

I would really love to be educated is there's something more
subtle to it.

> > 5) When I do
> >
> > cd
> > mkdir a
> > mntgen a
> > bind lib a/b
> > unmount a
> >
> > all these command finish ok, but I am left with
> >
> > bind /usr/ruda/lib /usr/ruda/a/b
> >
> > in the namespace (see the result of the 'ns' command; there you can also
> > spot that after issueing the 'mntgen' command a line
> > 'bind /usr/ruda/a /usr/ruda/a/' appears; that relates to my 4th question;
> > this bind is the one removed by the 'unmount' command).
> > How can I get rid of that then?
>
> i don't think any pruning of inaccessable bits of
> the namespace is ever done.  consider a program
> like ftpd which via /lib/namespace.ftp (sic) typically
> binds something like /usr/ftp/ onto /.  while everything
> above /usr/ftp is unaccessable, it's not removed from
> the namespace and you can't touch it.
>
> 	; mntgen a
> 	; bind /env a/env
> 	; bind /bin a/bin
> 	; bind /proc a/proc
> 	; bind a /
> 	; ns
>
> consider it a security feature.

Be it as it may, I still can't quite follow why *manual* pruning
of the entries from the namespace would be forbidden. unmount(2)
takes two strings as arguments, right? It doesn't even need an fd.

Thanks,
Roman.