|| ||Jamie Lokier <jamie-AT-shareable.org>|
|| ||Pavel Machek <pavel-AT-ucw.cz>|
|| ||Re: [PATCH] private mounts|
|| ||Tue, 26 Apr 2005 15:07:15 +0100|
|| ||Al Viro <viro-AT-parcelfarce.linux.theplanet.co.uk>,
Miklos Szeredi <miklos-AT-szeredi.hu>, hch-AT-infradead.org,
Pavel Machek wrote:
> > > Actually, after you add right mount xyzzy /foo lines into .profile,
> > > you can just . ~/.profile ;-).
> > Is there a mount command that can do that? We're talking about
> > private mounts - invisible to other namespaces, which includes the
> > other shells.
> > If there was a /proc/NNN/namespace, that would do the trick :)
> Sounds like the solution, then. I do not think Al Viro is going to
> kill you for /proc/NNN/namespace...
Looking closer, I think we already have it.
It's called /proc/NNN/root.
Does chroot into /proc/NNN/root cause the chroot'ing process to adopt
the namespace of NNN? Looking at the code, I think it does.
Furthermore, I think a daemon can acquire file descriptors for
multiple namespaces already, by open("/") and passing descriptors
between processes. And the chroot can be done using /proc/self/fd/N
after receiving a descriptor.
This is because file descriptors, and current->fs->pwd and
current->fs->root, record the vfsmnt as well as the dentry that they
So no new system calls are needed. A daemon to hand out per-user
namespaces (or any other policy) can be written using existing
kernels, and those namespaces can be joined using chroot.
That's the theory anyway. It's always possible I misread the code (as
I don't use namespaces and don't have tools handy to try them).
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