Re: [PATCH][CFT] per-process namespaces for Linux

From: Alexander Viro (
Date: Sun Feb 25 2001 - 19:26:24 EST

On Mon, 26 Feb 2001, Werner Almesberger wrote:

> Alexander Viro wrote:
> > No. Just an overmount.
> Ah, too bad. Union mounts would have been really elegant (allowing the
> operation to be repeated without residues, and also allowing umounting
> of the covered FS as a sanity check). But I guess there's no way to
> implement them without performance penalty ...

There is no way to implement them without credentials' cache. Which needs
to be done for many other reasons, but that's a separate patch and
separate story. If it's done - no serious penalty involved. However,
I doubt that we want a union on / itself. /dev - sure, /bin and /lib -
maybe, but /... What for?
> > Is it worth emptying?
> Probably not ... the only interesting case would be if you could completely
> umount it.

What's the point in unmounting it? Let the root of the mount tree be fixed -
it actually simplifies the things big way. Not that we had any performance
penalty for having the thing in place - after this forced chroot we never
touch it in lookups. BTW, pivot_root() is simpler that way.

BTW, we probably want to add mount --move <old> <new> - atomically moving
a subtree from one place to another. Code is there, we just need to
decide on API. Andries?

> So with some luck, distributors will switch to pivot_root sometime soon,
> when deploying 2.4. So if we drop all the old junk in 2.5, the amount of
> letter bombs should be small ;-)

Tomorrow I'll try to catch Erik and talk with him about that. I'm not sure
that I know anyone in Debian Install System Team (oh, boy... somebody sure
loved capital letters). And I've absolutely no idea who is doing that stuff
in other distributions...

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

This archive was generated by hypermail 2b29 : Wed Feb 28 2001 - 21:00:10 EST