Reload fstab without rebooting?

[uscla]

I have an SD card that I use overlay on:

# mkfs.ext4 /dev/mmcblk0
# mount /dev/mmcblk0 /mnt
# tar -C /overlay -cvf - . | tar -C /mnt -xf -
# umount /mnt
# block detect > /etc/config/fstab
# sed -i "s#/mnt/mmcblk0#/overlay#g" /etc/config/fstab
# sed -i "s/option\senabled\s'0'/option  enabled '1'/g" /etc/config/fstab

On reboot this works. However I want to do this without rebooting as this process is part of a set of setup scripts I'm writing to setup a new device. Is this possible?

Btw, I've tried:

# /etc/init.d/fstab stop
# /etc/init.d/fstab boot

And

# mount -a

And

# block umount
# block mount

None of which work. I do not see the SD card mounted on the overlay but /dev/mtdblock6 unless I reboot the device.

Edit-

Here is # df before reboot:

Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/root                 4352      4352         0 100% /rom
...
/dev/mtdblock6           10240      2816      7424  28% /overlay
overlayfs:/overlay       10240      2816      7424  28% /

And after:

Filesystem                Size      Used  Available Use% Mounted on
/dev/root                 4352      4352         0 100% /rom
...
/dev/mmcblk0             14.5G     40.3M      13.7G   0% /overlay
overlayfs:/overlay       14.5G     40.3M      13.7G   0% / 

[vgaetera]

You need to reboot since overlay is configured at the preinit stage.
Set up extroot as a child script/function and reboot at the end of the script.
Check if the overlay is mounted to avoid duplication before invoking the script.