[Qemu-devel] simulating a chroot-like interface with qemu

[Liraz Siri]

I'd like to run by you guys an idea I've been playing around with.

We've recently cut down in our use of qemu/kvm in our development
toolchain for TurnKey Linux and instead switched to using chroot for
many things, mainly because it is lighter and easier to script which
translates into reduced overhead during development.

On the flip side there are many downsides to using chroot:

* requires root privileges. You can get around this by giving a program
  suid privileges but that's dangerous because...
* root processes inside the chroot can easily break out
* processes inside the chroot share the network stack with processes
  outside the chroot.

  So for example, if mysql is running with the default configuration
  inside a VM and binds to port 3306 that will work even if the host is
  also running mysql listening to 3306. If you're using chroot  there is
  an additional overhead requiring you to reconfigure things.

* similarly, processes inside the chroot share the same abstract unix
  socket namespace, which complicates some usage scenarios...

I'm thinking maybe for some uses it would be useful to simulate an
interface that looks and functions like chroot but is magically
implemented with qemu/kvm behind the scenes (e.g., separate kernel,
network stack, etc.).  Sort of a power chroot that offers stronger
isolation/compartmentalization but with a similar unixish interface
(e.g., pipeable, scriptable, etc.)

Perhaps rather than mounting a block device, the guest could access its
root in the host filesystem transparently via a network filesystem of
some kind.

What do you think? Has anyone tried to use qemu to do something like
this before? Would it be difficult to implement?

Cheers,
Liraz