So obviously ubiattach is the way to go. My real questions is "what are the consequences of doing so?".
Vanilla available disk space on my Netgear WAX202.
root@OpenWRT:~# df -h
Filesystem Size Used Available Use% Mounted on
/dev/root 4.0M 4.0M 0 100% /rom
tmpfs 248.9M 1.2M 247.8M 0% /tmp
/dev/ubi0_1 22.3M 7.5M 13.6M 36% /overlay
overlayfs:/overlay 22.3M 7.5M 13.6M 36% /
tmpfs 512.0K 0 512.0K 0% /dev
All raw block devices:
root@OpenWRT:~# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINTS
mtdblock0 31:0 0 512K 1 disk
mtdblock1 31:1 0 512K 1 disk
mtdblock2 31:2 0 512K 1 disk
mtdblock3 31:3 0 38M 0 disk
mtdblock4 31:4 0 4M 0 disk
mtdblock5 31:5 0 34M 0 disk
mtdblock6 31:6 0 38M 1 disk
mtdblock7 31:7 0 8M 1 disk
mtdblock8 31:8 0 4M 1 disk
mtdblock9 31:9 0 1M 1 disk
mtdblock10 31:10 0 4M 1 disk
mtdblock11 31:11 0 2M 1 disk
mtdblock12 31:12 0 1M 1 disk
mtdblock13 31:13 0 1M 1 disk
mtdblock14 31:14 0 5M 1 disk
mtdblock15 31:15 0 1M 1 disk
mtdblock16 31:16 0 6.3M 1 disk
ubiblock0_0 254:0 0 4M 0 disk /rom
If I add up the /dev/mtdblock*, I get 148, which is close to the 128M reported on the device page.
I looks like only /dev/mdtblock5 is attached to ubi (Is there really no ubi* command to show this?)
root@OpenWRT:~# cat /sys/devices/virtual/ubi/ubi0/mtd_num
5
Assuming a bit of overhead, that looks to about match the UBI config:
root@OpenWRT:~# ubinfo -a
UBI version: 1
Count of UBI devices: 1
UBI control device major/minor: 10:62
Present UBI devices: ubi0
ubi0
Volumes count: 2
Logical eraseblock size: 126976 bytes, 124.0 KiB
Total amount of logical eraseblocks: 272 (34537472 bytes, 32.9 MiB)
Amount of available logical eraseblocks: 0 (0 bytes)
Maximum count of volumes 128
Count of bad physical eraseblocks: 0
Count of reserved physical eraseblocks: 20
Current maximum erase counter value: 3
Minimum input/output unit size: 2048 bytes
Character device major/minor: 250:0
Present volumes: 0, 1
Volume ID: 0 (on ubi0)
Type: dynamic
Alignment: 1
Size: 33 LEBs (4190208 bytes, 3.9 MiB)
State: OK
Name: rootfs
Character device major/minor: 250:1
-----------------------------------
Volume ID: 1 (on ubi0)
Type: dynamic
Alignment: 1
Size: 215 LEBs (27299840 bytes, 26.0 MiB)
State: OK
Name: rootfs_data
Character device major/minor: 250:2
Can I just ubiattach -p /dev/mtdblock3 and possibly all the other mtd devices to get my 128M of disk space? I assume not. I think at least one of those devices is used for firmware upgrades and rollbacks and such. Is there any way to figure out which one and use the rest?