Skeleton /init for minimal initramfs

#!/command/execlineb -S0

# Skeleton /init for minimal initramfs.
# (C) 2016-2017 Laurent Bercot, wtfpl license.

/command/export PATH /command
/command/cd /
if { s6-echo "\n  initramfs (minimal)\n" }

if { s6-mount -wt sysfs sys /sys }
if { s6-mount -wt proc proc /proc }

# Just in case the kernel config says not to mount devtmpfs at boot
foreground { redirfd -w 2 /dev/null s6-mount -wt devtmpfs dev /dev }

# If you need to manually load modules, do it here, but in some cases the
# coldplug will initiate request_module() actions, so depending on the
# hardware you're expecting, you could have a /sbin/modprobe and a
# /etc/mdev.conf with a MODALIAS definition instead.
# If you have hardware with weird /sys definitions, or expect
# specific /dev devices, you should definitely have an appropriate
# /etc/mdev.conf anyway.

if { redirfd -w 1 /proc/sys/kernel/hotplug s6-echo /sbin/mdev }
if { /sbin/mdev -s }  # coldplug
if { redirfd -w 1 /proc/sys/kernel/hotplug s6-echo }

# Coldplug done, you have a snapshot of your hardware in /dev.
# Now you need to name your rootfs and its type; you can hardcode them
# like it's done here, or substitute ROOTFS and ROOTFSTYPE with the
# result of your rootfs detection.

define ROOTFS sda1      # Replace with your own
define ROOTFSTYPE ext4  # detection routines!

if { s6-mount -rt ${ROOTFSTYPE} /dev/${ROOTFS} /rootfs }

if { s6-mount -o move /sys /rootfs/sys }
if { s6-mount -o move /proc /rootfs/proc }
if { s6-mount -o move /dev /rootfs/dev }

cd /rootfs

# OK, all done. Now we're going to delete everything in the initramfs,
# so we're relying on binaries existing in the rootfs to do our job
# in order to avoid sweeping the rug off our own feet.
# You could use busybox's switch_root instead, but you'll still
# have to rely on binaries existing on the rootfs after you
# chroot into it.

./command/if
{
  ./command/pipeline { ./command/s6-ls -a -x rootfs / }
  ./command/forstdin -p -d"\n" i
  ./command/importas -u i i
  ./command/s6-rmrf /${i}
}
./command/if { ./command/s6-mount -o move . / }
./command/s6-chroot .

/command/unexport ?
/command/unexport PATH
/command/tryexec { /sbin/init $@ }
/command/tryexec { /bin/init $@ }
/etc/init $@