[OE-core] RFC: meta-ro-rootfs approach and volatiles vs tmpfiles.d

[Colin Walters]

On Wed, 2013-07-24 at 11:54 -0700, Chris Larson wrote:

>   - Patched in --sysroot= support for systemd-tmpfiles, to facilitate
> running it up front against the filesystem at do_rootfs time the way
> read_only_rootfs_hook does with populate-volatiles

How are you handling /run?  Is it still a tmpfs in your model?  If so
are you excluding tmpfiles.d snippets which reference /run at rootfs
time?

It strikes me that a less invasive way to achieve readonly rootfs is
to symlink /var -> /run/var.  Or are you doing that already?

Then you'd probably want to just run through any tmpfiles which
reference /etc and /usr.

> 
> - Implemented a prototype configuration for dbus which uses this to
> support read-only-rootfs. 

Err...for what?  /var/run/dbus/system_bus_socket?  You should just
have /var/run -> /run, and that's solved.

If it's for /var/lib/dbus/machine-id, likewise that should on modern
systems just be a symlink to /etc/machine-id.

Though you do need to figure out whether you want a statically
configured machine ID, or to have one generated dynamically at boot.
These both have tradeoffs; basically, whatever you're doing for the
random seed you should probably also do for the machine ID.