This is an almost step by step tutorial for installing a modified OpenWrt (luci removed usb storage support added) Firmware to A5-V11 Mini Router using the information from these sites:

https://wiki.openwrt.org/toh/unbranded/a5-v11

https://wiki.openwrt.org/doc/howto/extroot

Bootloader image file uboot256.bin is taken from this site:

https://github.com/wertwert4pda/rt5350f-uboot

Kernel image file firmware.bin is generated using this command:

make image PROFILE="A5-V11" PACKAGES="-luci nano blkid block-mount kmod-nls-cp437 kmod-nls-iso8859-1 kmod-nls-utf8 kmod-fs-vfat kmod-fs-ext4 kmod-usb-storage-extras"

Image build instructions are taken from this site:

https://wiki.openwrt.org/doc/howto/obtain.firmware.generate

Insert a Fat32 formatted USB flash drive to the device USB, connect to it's Wi-Fi and TELNET to 192.168.100.1 (username/password is admin/admin) to enter these commands:

umount /dev/sda1
mount /dev/sda1 /mnt
mtd_write write /mnt/uboot256.img Bootloader
mtd_write write /mnt/firmware.bin Kernel
reboot

When you reboot the Wi-Fi is disabled and Ethernet IP becomes 192.168.1.1 so you must connect the device to your computer via ethernet cable and configure your computer with Static IP like 192.168.1.2 and TELNET again.

Enter passwd to assign a password to root and exit TELNET, SSH to 192.168.1.1 with your newly created password.

First you must gain internet access for using opkg to install luci and other packages.

nano /etc/config/network

Change these lines in the config interface 'lan' section according to your network:

option ipaddr '192.168.2.254'
option netmask '255.255.255.0'

Add these lines after the netmask line:

option gateway '192.168.2.1'
option dns '192.168.2.1'

And enter reboot again and connect the device to your modem/switch with ethernet cable. SSH to your newly configured IP address and check if you are connected to internet:

ping -c 4 google.com

Prepare a USB flash drive at a Linux machine and make three partitions:

Overlay (1 GiB): primary boot ext4
Swap (512 MiB): primary swap
Data (Rest): primary ext4

Plug the USB flash drive and enter this command (all at once) to create fstab and enable partitions:

block detect > /etc/config/fstab; \
   sed -i s/option$'\t'enabled$'\t'\'0\'/option$'\t'enabled$'\t'\'1\'/ /etc/config/fstab; \
   sed -i s#/mnt/sda1#/overlay# /etc/config/fstab; \
   sed -i s#/mnt/sda3#/data# /etc/config/fstab; \
   cat /etc/config/fstab;

Configure opkg to use extra space and create a mount folder /data for the third partition:

echo option force_space >> /etc/opkg.conf
mkdir /data

Copy current /overlay to the 1 GiB partition:

umount /dev/sda1
mount /dev/sda1 /mnt
tar -C /overlay -cvf - . | tar -C /mnt -xf -
reboot

At this step you should see the free space has grown when you use the df command and overlay is mounted as /dev/sda1 when you use the mount command.

Reinstall luci to your much bigger extroot space:

opkg update
opkg install luci

You now should have a fully functional OpenWrt with a Web UI (luci) and a lot of space to install whatever you want.

My first recommendations are:

opkg install mc e2fsprogs fdisk
opkg install mosquitto mosquitto-client libmosquitto 

The following are optional upgrade/restore instructions.

umount /dev/sda1
mount /dev/sda1 /mnt
mtd -r write /mnt/firmware.bin firmware

firstboot
rm -r /overlay/upper/*
rm -r /overlay/*
mtd -r erase rootfs_data