How to mount f2fs from the same mmc partition as sqashfs?

[m95d]

Turris Omnia. MMC is partitioned like this:

# lsblk
NAME         MAJ:MIN RM   SIZE RO TYPE MOUNTPOINTS
loop0          7:0    0 195.7M  0 loop /overlay    <--- f2fs
mtdblock0     31:0    0   960K  0 disk 
mtdblock1     31:1    0     7M  0 disk 
mtdblock2     31:2    0    64K  0 disk 
mmcblk0      179:0    0   7.3G  0 disk 
├─mmcblk0p1  179:1    0  16.3M  0 part 
└─mmcblk0p2  179:2    0 240.3M  0 part /rom    <--- squashfs
mmcblk0boot0 179:8    0     4M  1 disk 
mmcblk0boot1 179:16   0     4M  1 disk 
zram0        254:0    0     0B  0 disk 

# losetup -a
/dev/loop0: 46727168 /dev/mmcblk0p2    <--- f2fs

mmcblk0p2 starts with a squashfs, followed by a "hidden" f2fs filesystem in the same partition.

I usually mount overlay from USB. Sometimes I need to change the extroot parameters in /etc/config/fstab from f2fs.

How do I manually mount that hidden f2fs from mmcblk0p2?

Thanks.

[brada4]

mount_root or repeat losetup command.

[m95d]

mount_root in a running system would probably make a mess of all the mounts.

And what is the losetup command? The usual losetup would probably expose just the squasfs, not the f2fs.

[brada4]

Last line after losetup command shows offset where overlay starts.

[m95d]

Where do I find that offset in a system that booted extroot and how do I use it?

PS: I know how to use it. losetup -o <offset>. I still don't know where to find it.

[brada4]

@m95d

loop0: 46727168 /dev/

good morning...

[m95d]

Helloooo.... That changes every time I build a new fw image! That's ... daily.

[brada4]

There is no other reference about offset, you can scan for f2fs magic after end of squashfs, still hackish.

[m95d]

Damn it! Who tf had the ideea to put two filesystems in the same partition??

[brada4]

Add another data filesystem on USB and dont break your head about them