OpenWrt Forum Archive

Post #1

ssparks

21 Jun 2017, 14:44

I am customzing OpenWRT to run on a Gateworks Ventana 5220, and am booting of a micro-SD card. I would like to overlay two separate partitions that are both mounted read-only as the root partition, but haven't had much luck.

My troubles include:
1) OpenWRT overrides the kernel command line, and always mounts the root partition as rw
2) Despite editing /etc/config/fstab to mount the secondary partition on target /overlay, it doesn't get overlayed with the rootfs

For problem 1, i'm successfully passing in the ro option to the kernel command line, but mount shows the root filesystem as rw. How do I go about configuring a ro ext4 root partion?

# cat /proc/cmdline
console=ttymxc1,115200 root=/dev/mmcblk0p1 rootfstype=ext4 rootwait ro
# mount
/dev/root on / type ext4 (rw,noatime,data=ordered)
proc on /proc type proc (rw,nosuid,nodev,noexec,noatime)
sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,noatime)
tmpfs on /tmp type tmpfs (rw,nosuid,nodev,noatime)
tmpfs on /dev type tmpfs (rw,nosuid,relatime,size=512k,mode=755)
devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,mode=600)
debugfs on /sys/kernel/debug type debugfs (rw,noatime)

For problem 2, I've edited my /etc/config/fstab as follows, and I see the /overlay directory is being mounted. However, the contents of /overlay are not showing up under /. How do i configure openwrt to overlay the two partitions as root?

# cat /etc/config/fstab
config 'global'
        option  anon_swap       '0'
        option  anon_mount      '0'
        option  auto_swap       '1'
        option  auto_mount      '1'
        option  delay_root      '5'
        option  check_fs        '0'

config 'mount'
        option  target  '/mnt/mmcblk0p1'
        option  uuid    '47f4cc43-be14-41a5-9b0b-9a65d5b14727'
        option  enabled '0'

config 'mount'
        option  target  '/mnt/mmcblk0p2'
        option  uuid    'd88ac5b2-30ea-4202-add6-96627c183fa6'
        option  enabled '0'

config 'mount'
        option  device  '/dev/mmcblk0p3'
        option  target  '/overlay'
        option  enabled '1'

config 'mount'
        option  target  '/mnt/mmcblk0p5'
        option  uuid    '87181c52-ce63-4cbc-b89d-1d732bd8744e'
        option  enabled '0'

config 'mount'
        option  target  '/mnt/mmcblk0p6'
        option  uuid    '2f3b58c7-502f-4218-9adf-5d190febe7f0'
        option  enabled '0'

local directory exists on the overlay but not on root.

# ls /overlay/usr/
local
# ls /usr/
bin    lib    sbin   share

Thanks for the help!

Post #2

elektroman

21 Jun 2017, 19:41

IIRC look here

/lib/functions/preinit.sh

Post #3

ssparks

21 Jun 2017, 22:11

Looking through the preinit scripts, libfstools, and re-reviewing the wiki pages on extroot and preinit indicates openwrt doesn't support this outside of squashfs/jffs2 filesystems. There is a lot of decisions built into the initialization process that assumes flash memory is used for the booting disk.

Looks like I'll be doing some heavy customization. Thanks!