https://blog.csdn.net/qq_24649627/article/details/128834264
Package need to be installed:
* parted
* losetup
* resize2fs

OpenWRT use ext4 file system.

use ssh to OpenWRT, eg. 192.168.1.1
1: command type "parted" to show current partations
2: parted -s /dev/mmcblk0 resizepart 2 100%
3: losetup /dev/loop0 /dev/mmcblk0p2
4: resize2fs -f /dev/loop0
5: reboot
8: df-h <= print partations on screen.