sonic-buildimage/files/initramfs-tools/union-mount.j2

#!/bin/sh -e

PREREQS="varlog"

prereqs() { echo "$PREREQS"; }

case $1 in
  prereqs)
  prereqs
    exit 0
    ;;
esac

## Mount the overlay file system: rw layer over squashfs
image_dir=$(cat /proc/cmdline | sed -e 's/.*loop=\(\S*\)\/.*/\1/')
mkdir -p ${rootmnt}/host/$image_dir/rw
mkdir -p ${rootmnt}/host/$image_dir/work
mount -n -o lowerdir=${rootmnt},upperdir=${rootmnt}/host/$image_dir/rw,workdir=${rootmnt}/host/$image_dir/work -t overlay root-overlay ${rootmnt}
## Check if the root block device is still there
[ -b ${ROOT} ] || mdev -s
## Mount the raw partition again
mount ${ROOT} ${rootmnt}/host

mkdir -p ${rootmnt}/var/lib/docker
if [ -f ${rootmnt}/host/$image_dir/{{ FILESYSTEM_DOCKERFS }} ]; then
    ## mount tmpfs and extract docker into it
    mount -t tmpfs -o rw,nodev,size={{ DOCKER_RAMFS_SIZE }} tmpfs ${rootmnt}/var/lib/docker
    tar xz --numeric-owner -f ${rootmnt}/host/$image_dir/{{ FILESYSTEM_DOCKERFS }} -C ${rootmnt}/var/lib/docker
else
    ## Mount the working directory of docker engine in the raw partition, bypass the overlay
    mount --bind ${rootmnt}/host/$image_dir/{{ DOCKERFS_DIR }} ${rootmnt}/var/lib/docker
fi

## Mount the boot directory in the raw partition, bypass the overlay
mkdir -p ${rootmnt}/boot
mount --bind ${rootmnt}/host/$image_dir/boot ${rootmnt}/boot
## Mount loop device for /var/log
[ -f ${rootmnt}/host/disk-img/var-log.ext4 ] && mount -t ext4 -o loop,rw ${rootmnt}/host/disk-img/var-log.ext4 ${rootmnt}/var/log