zfs_20070303.patch on current

Pawel Jakub Dawidek pjd at FreeBSD.org
Mon Mar 12 14:30:19 UTC 2007


On Mon, Mar 12, 2007 at 10:06:49AM +0100, Dag-Erling Sm?rgrav wrote:
> Barry Pederson <bp at barryp.org> writes:
> > Is there any hope for someday optionally using ZFS as a root filesystem?
> 
> For that to be possible, both /boot/boot2 and /boot/loader need to
> understand ZFS well enough to read files from it.  There isn't much
> room to spare in /boot/boot2, so we'd have to have a separate version
> for ZFS and teach 'disklabel -B' how to pick the right one.

This would be hard, I fully agree.

> > I was sort of imagining a setup where /boot resided in a UFS
> > filesystem so it could hold the kernel/modules/regular booting info
> > and -
> > /boot/loader.conf would specify 'zfs_load="YES"' along with another
> > directive to tell which zfs filesystem to use as root.
> 
> Unlike Linux, where this is a common configuration, FreeBSD can't
> mount a root filesystem underneath an already mounted /boot
> filesystem. [...]

We don't have to mount /boot/ to read from it. The loader reads directly
from boot partition, so bascially we could make /dev/ad0s1a a small UFS
partition that contains the kernel, zfs kernel module and /etc/fstab
and it should work. Note that we currently allow for encrypting root
file system the same way with geli(8).

> [...] Nor do we have anything resembling Linux's pivot_root
> which would allow us to mount the root filesystem on top of /boot and
> then switch them around.

Actually we do something like this for devfs, AFAIK - we first mount
devfs as root file system, then we mount the right root on top of it and
move devfs to /dev/.

-- 
Pawel Jakub Dawidek                       http://www.wheel.pl
pjd at FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!
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