On 21.01.2014 08:30, Colin Walters wrote:
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.
Thanks for the information. I think I was thrown off by the fact that
the root device is mounted in several places with different content but
now I realize that's probably because the "external" path isn't
available from inside the jail so mount can only display the device.
Previously I've only used bind mounts in a non-chroot context.
Regards,
Dennis
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