Warn about libvirt with SDL in maverick

[Serge Hallyn]

Maverick moves .Xauthority from $HOME into a new location randomly
selected at login, namely /var/run/gdm/auth-for-$USER/-$RANDOM/database.

Virt-manager by default creates vnc connections, but users can specify
SDL. SDL requires use of .Xauthority, and libvirt still expects it under $HOME.
This causes two problems:

1. libvirt needs to get the .Xauthority location at run-time from the user's
environment. It can't be encoded in the .xml file since it will change.

2. libvirt launches qemu-kvm as an unprivileged user who cannot access
the invoking user's .Xauthority.

Solving this will likely require some upstream work. In the meantime, the
release notes should be updated to

1. warn against using SDL

and/or

2. provide a workaround. For instance, the user might be advised to
 a) specify that libvirt should start qemu privileged, by specifying
     user and group root in /etc/libvirt/qemu.conf
 b) editing each VMs definition after each reboot to point to the new
     location
or, as an alternative to b,
 b) run a script as root which symlinks or bind mounts the actual
    auth file to $HOME/.Xauthority.

[Scott Kitterman (kitterman)]

Did Xauthority move for all *dm or just gdm? If it's just gdm, then perhaps
installing kdm and logging in using it would be a viable work around?

[Jamie Strandboge (jdstrand)]

Rather than running as root:root, perhaps the VMs can continue to run unprivileged and adjust the .Xauthority file's permissions to 640 with group 'kvm'. If you are going to recommend to run as root:root, then you should reiterate that VMs are confined by individual apparmor profiles.