on my sdcard there is a 20MB fat16 boot partition and a 104MB unknown partition
Gparted does not let me resize the 104MB partition because it is unknown.
What should i do?
To resize the squashfs-image one has to know the offset of the hidden f2fs filesystem. In this example, the squashfs partiton is /dev/sde2.
1.You can find the offset, by running losetup on your openwrt device.
2.On your computer, resize the squashfs partition, for example with cfdisk.
3.Loop mount the underlying f2fs partition 2)
losetup -d -o <offset> /dev/loop0 /dev/sde2
4.Run filesystem checks
5. Resize f2fs filesystem
Now your filesystem should be recognized with the correct size.
I have not used those specific steps in the wiki but I think they can be done either on a linux / mac computer or on the OpenWrt device with the needed utilities installed.
A modified procedure works well run on NanoPi R4S routers with anaelorlinski builds or the standard OpenWrt builds which has a f2fs filesystem as the hidden writable filesystem in the squashfs image.
I found that using the imagebuilder to create an image with extra packages produces a squashfs image with a hidden ext4 filesystem after first boot so I successfully modified anaelorlinski's script to use the ext4 resizing tool.
Note that these "scripts" are a list of commands to be typed or pasted on the router command line one at a time. Do not copy/paste all of them at once and stop if you get an error.
Be sure to have your router configuration backed up before doing this and also have the list of any manually installed packages saved on your computer (someplace off the sd card you are modifying).
In case you are not aware, everything on the sd card gets wiped out with each sysupgrade so your filesystem expansion needs to be redone and all the data needs to be restored from backups etc.