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|
#!/bin/sh
# Enable strict shell mode
set -euo pipefail
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MOUNT="/bin/mount"
UMOUNT="/bin/umount"
INIT="/sbin/init"
ROOT_ROINIT="/sbin/init"
ROOT_MOUNT="/mnt"
ROOT_RODEVICE=""
ROOT_RWDEVICE=""
ROOT_ROMOUNT="/media/rfs/ro"
ROOT_RWMOUNT="/media/rfs/rw"
ROOT_RWRESET="no"
early_setup() {
mkdir -p /proc
mkdir -p /sys
$MOUNT -t proc proc /proc
$MOUNT -t sysfs sysfs /sys
grep -w "/dev" /proc/mounts >/dev/null || $MOUNT -t devtmpfs none /dev
}
read_args() {
[ -z "${CMDLINE+x}" ] && CMDLINE=`cat /proc/cmdline`
for arg in $CMDLINE; do
# Set optarg to option parameter, and '' if no parameter was given
optarg=`expr "x$arg" : 'x[^=]*=\(.*\)' || echo ''`
case $arg in
root=*)
ROOT_RODEVICE=$optarg ;;
rootfstype=*)
modprobe $optarg 2> /dev/null || true;;
rootinit=*)
ROOT_ROINIT=$optarg ;;
rootrw=*)
ROOT_RWDEVICE=$optarg ;;
rootrwfstype=*)
modprobe $optarg 2> /dev/null || true;;
rootrwreset=*)
ROOT_RWRESET=$optarg ;;
init=*)
INIT=$optarg ;;
esac
done
}
fatal() {
echo $1 >$CONSOLE
echo >$CONSOLE
exec sh
}
early_setup
[ -z "${CONSOLE+x}" ] && CONSOLE="/dev/console"
read_args
mount_and_boot() {
mkdir -p $ROOT_MOUNT $ROOT_ROMOUNT $ROOT_RWMOUNT
# Build mount options for read only root filesystem.
# If no read-only device was specified via kernel commandline, use current
# rootfs via bind mount.
ROOT_ROMOUNTOPTIONS_BIND="-o bind,ro /"
if [ -z "${ROOT_RODEVICE}" ]; then
ROOT_ROMOUNTOPTIONS="${ROOT_ROMOUNTOPTIONS_BIND}"
else
ROOT_ROMOUNTOPTIONS="-o ro,noatime,nodiratime $ROOT_RODEVICE"
fi
# Mount rootfs as read-only to mount-point, if unsuccessful,
# try bind mount current rootfs
if ! $MOUNT $ROOT_ROMOUNTOPTIONS $ROOT_ROMOUNT && \
! $MOUNT $ROOT_ROMOUNTOPTIONS_BIND $ROOT_ROMOUNT; then
fatal "Could not mount read-only rootfs"
fi
# If future init is the same as current file, use $ROOT_ROINIT
# Tries to avoid loop to infinity if init is set to current file via
# kernel commandline
if cmp -s "$0" "$INIT"; then
INIT="$ROOT_ROINIT"
fi
# Build mount options for read write root filesystem.
# If no read-write device was specified via kernel commandline, use tmpfs.
if [ -z "${ROOT_RWDEVICE}" ]; then
ROOT_RWMOUNTOPTIONS="-t tmpfs -o rw,noatime,mode=755 tmpfs"
else
ROOT_RWMOUNTOPTIONS="-o rw,noatime,mode=755 $ROOT_RWDEVICE"
fi
# Mount read-write filesystem into initram rootfs
if ! $MOUNT $ROOT_RWMOUNTOPTIONS $ROOT_RWMOUNT ; then
fatal "Could not mount read-write rootfs"
fi
# Reset read-write filesystem if specified
if [ "yes" == "$ROOT_RWRESET" -a -n "${ROOT_RWMOUNT}" ]; then
rm -rf $ROOT_RWMOUNT/*
fi
# Determine which unification filesystem to use
union_fs_type=""
if grep -w "overlay" /proc/filesystems >/dev/null; then
union_fs_type="overlay"
elif grep -w "aufs" /proc/filesystems >/dev/null; then
union_fs_type="aufs"
else
union_fs_type=""
fi
# Create/Mount overlay root filesystem
case $union_fs_type in
"overlay")
mkdir -p $ROOT_RWMOUNT/upperdir $ROOT_RWMOUNT/work
$MOUNT -t overlay overlay -o "lowerdir=$ROOT_ROMOUNT,upperdir=$ROOT_RWMOUNT/upperdir,workdir=$ROOT_RWMOUNT/work" $ROOT_MOUNT
;;
"aufs")
$MOUNT -t aufs -o "dirs=$ROOT_RWMOUNT=rw:$ROOT_ROMOUNT=ro" aufs $ROOT_MOUNT
;;
"")
fatal "No overlay filesystem type available"
;;
esac
# Move read-only and read-write root filesystem into the overlay filesystem
mkdir -p $ROOT_MOUNT/$ROOT_ROMOUNT $ROOT_MOUNT/$ROOT_RWMOUNT
$MOUNT -n --move $ROOT_ROMOUNT ${ROOT_MOUNT}/$ROOT_ROMOUNT
$MOUNT -n --move $ROOT_RWMOUNT ${ROOT_MOUNT}/$ROOT_RWMOUNT
$MOUNT -n --move /proc ${ROOT_MOUNT}/proc
$MOUNT -n --move /sys ${ROOT_MOUNT}/sys
$MOUNT -n --move /dev ${ROOT_MOUNT}/dev
cd $ROOT_MOUNT
# busybox switch_root supports -c option
exec chroot $ROOT_MOUNT $INIT ||
fatal "Couldn't chroot, dropping to shell"
}
mount_and_boot
|
