Announce: fedostree/rpm-ostree v2014.3

[Colin Walters]

Hi Dennis,

On Tue, 2014-01-21 at 07:40 +0100, Dennis Jacobfeuerborn wrote:

> Interesting. I've downloaded the VM Image and tried to understand the 
> setup. 

Some bits are documented here
https://people.gnome.org/~walters/ostree/doc/layout.html

> Apparently there exist sort of two root trees / and /sysroot in 
> the system with some links targeting the /sysroot tree. 

With OSTree, you boot directly into a chroot - dracut switches root and
starts systemd right after mounting the rootfs.  See:
https://git.gnome.org/browse/ostree/tree/src/switchroot/ostree-prepare-root.c

/sysroot is a bind mount to the real root /.

> What I'm 
> wondering about is that /dev/mapper/fedora-root is mounted several times 
> on /, /var, /usr and /sysroot (twice!) sometimes rw and sometimes ro.

/usr is simply a bind mount to itself so it can be mounted read-only.
This is important because otherwise one could corrupt the object store
in /ostree/repo by mutating the hardlink farm in /usr.

Note the /usr here is
really /ostree/deploy/fedostree/deploy/<checksum.serial>/usr as seen
from the physical root.

/var is a special bind mount to /ostree/deploy/fedostree/var which is
shared between each deployment (chroot).

> The impression I get is that /sysroot is the actual root fs in the image 
> and / the ostree directory at least that's what the links seem to 
> suggest. I still don't understand the mount-voodoo though. Is there some 
> documentation about this available?

I'll look at adding more to the gtk-doc, though I suspect I may need to
make a separate "system administrators new to OSTree" document which is
a bit distinct from the "how to use OSTree underneath your package
manager" document that the current one is.