[systemd-devel] OSTree mount integration
walters at verbum.org
Mon Sep 24 15:12:39 PDT 2012
On Mon, 2012-09-24 at 22:19 +0200, Lennart Poettering wrote:
> i.e. my suggestion would be to patch dracut (or write a dracut module)
> that sets up your target OS tree with /var and friends directly, and
> then transitions directly to it via moving it to / rather than first
> moving into the host OS tree via a move/bind mount and then using
> chroot() for the second step. (That said, whether you do this in one or
> two steps is not important, what is important however is that you do not
> use chroot()).
For reference by the way, the current ostree_switch_root code that gets
called from dracut is here:
(It's a fork of util-linux switch_root).
The issue with your suggestion I think is that the "deployment root" as
I call them (ostree chroots) isn't a mount point, so I can't just
MS_MOVE move the whole directory to /. Although I can make it into a
mount point I guess with the trick of bind-mounting it to itself, and
then move that?
Hm. So something something like this, from dracut's perspective,
where /sysroot is the "target rootfs", and its / is the initramfs:
I may try this and see if it works.
But I don't think this will exactly the solve all the problems. In this
case / is still a bind mount, not the real backing store. So for
example if I have a normal / entry in /etc/fstab, systemd is going to
fail to remount it read/write.
(Right now, rather hackily, I just remount the backing store r/w in
One notable complication with this whole setup is the read-only bind
mount over /usr (and /bin, /lib at the moment), which I've elided from
> I am not totally against that, but I'd really like to keep explicit
> virtualization checks at a minimum and use them as solution only if
> nothing else works nicely.
Right, definitely agree. But even with the above setup I'm not sure how
we can completely avoid it.
I should get a chance to try out some patches here within a few weeks.
The main thing that needs fixing is /etc/fstab :
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