The current switch_root can only switch to a new root that is the root
of a mount point.
This patch adds support for "subroots", where the new root is somewhere
below a mount point. It does this by adding in a few extra steps to
chroot into the subroot after the enclosing partition has been moved
and entered.
This will be used by OLPC, who sort-of have 2 copies of Fedora stored
on a single partition under different directory trees, where the
initramfs decides which one to boot into.
TODO: /etc/passwd and /etc/group are not removed yet due to 90mdraid.
dledford said he'll go in and clean this up since he has the hardware
to actually test the mdmon stuff.
init now has the following points to inject scripts:
/cmdline/*.sh
scripts for command line parsing
/pre-udev/*.sh
scripts to run before udev is started
/pre-trigger/*.sh
scripts to run before the main udev trigger is pulled
/initqueue/*.sh
runs in parallel to the udev trigger
Udev events can add scripts here with /sbin/initqueue.
If /sbin/initqueue is called with the "--onetime" option, the script
will be removed after it was run.
If /initqueue/work is created and udev >= 143 then this loop can
process the jobs in parallel to the udevtrigger.
If the udev queue is empty and no root device is found or no root
filesystem was mounted, the user will be dropped to a shell after
a timeout.
Scripts can remove themselves from the initqueue by "rm $job".
/pre-mount/*.sh
scripts to run before the root filesystem is mounted
NFS is an exception, because it has no device node to be created
and mounts in the udev events
/mount/*.sh
scripts to mount the root filesystem
NFS is an exception, because it has no device node to be created
and mounts in the udev events
If the udev queue is empty and no root device is found or no root
filesystem was mounted, the user will be dropped to a shell after
a timeout.
/pre-pivot/*.sh
scripts to run before the real init is executed and the initramfs
disappears
All processes started before should be killed here.
The behaviour of the dmraid module demonstrates how to use the new
mechanism. If it detects a device which is part of a raidmember from a
udev rule, it installs a job to scan for dmraid devices, if the udev
queue is empty. After a scan, it removes itsself from the queue.
it solves the following case:
root=/dev/nfs nfsroot=server:/path
- the server could be reachable on any interface
- any interface can get an IP by dhcp
- only one IP is allowed to mount the root
Udev rules set a /dev/root symlink to the real root and add
a mount script to /mount/. This enables the proper use of pre-mount
scripts and prevents mount being killed by a udev timeout.
Daniel Drake