- vfat => vfat | squashfs + ext4(overlay)
root@OpenWrt:/# blkid
/dev/loop0: LABEL="rootfs_data" UUID="x-x-x" TYPE="ext4"
/dev/mmcblk1: PTUUID="x-x-x" PTTYPE="dos"
/dev/mmcblk1p1: SEC_TYPE="msdos" LABEL="OW_BOOT" UUID="DEAD-BEEF" TYPE="vfat" PARTUUID="x-x-x"
/dev/mmcblk1p2: TYPE="squashfs" PARTUUID="x-x-x"
root@OpenWrt:/# losetup
NAME SIZELIMIT OFFSET AUTOCLEAR RO BACK-FILE DIO LOG-SEC
/dev/loop0 0 25427968 0 0 /mmcblk1p2 0 512
root@OpenWrt:/# cat /proc/mounts
/dev/root /rom squashfs ro,relatime 0 0
devtmpfs /rom/dev devtmpfs rw,relatime,size=469452k,nr_inodes=117363,mode=755 0 0
tmpfs /tmp tmpfs rw,nosuid,nodev,noatime 0 0
/dev/loop0 /overlay ext4 rw,noatime 0 0
overlayfs:/overlay / overlay rw,noatime,lowerdir=/,upperdir=/overlay/upper,workdir=/overlay/work 0 0