Re: [9fans] v9fs question

[Tim Newsham <newsham@lava.net>]

> Could we solve this by making private mounts the default (or only
> allowed) behavior?

I've wondered if there's enough context information
that the fs driver could "fake" per-process mount points
directly.  For example, I mount v9fs on /n.  Initially
I have no remote mounts in there, but I have /n/ctl.
I echo "mount 1.2.3.4 foo" to /n/ctl and now I have
/n/foo which is served from 1.2.3.4 for my process, but
other processes dont see /n/foo.  I fork a child and it
gets /n/foo, too.  In the child I mount another directory
and the changes are seen in both the child and the parent.
I then echo "copyns" to /n/ctl and then perform another
mount and the new mount is visible in the child process but
not the parent process.

This would of course require that the kernel filesystem
(probably vfs layer) could distinguish who made a filesystem
request.  It might also require some hackery to get the
inheritance on fork working properly (although perhaps some
existing unix mechanism could be reused for this purpose, such
as session and process group stuff).

Feasible at all in Linux? *BSD?  Win32?

Upsides: Kernel doesnt need to otherwise support any notion
of mount namespace.  Removes security concerns of per-process
namespaces since you could never rebind over /etc/passwd or
other important files.

Downsides: Perhaps not possible.  Mount/bind namespaces not
universally present, only within certain mount points.

> ron

Tim Newsham
http://www.thenewsh.com/~newsham/