MTD : cannot reserve enough PEBs for bad PEB handling

[Mark Jackson <mpfj-list@newflow.co.uk>]

I'm trying to work out how to generate a "valid" UBI image, but I keep
getting a "cannot get enough PEBs" warning.

I generate my image (destined for a 64MB NAND partition) using:-

$ mkfs.ubifs -d output/target -e 0x1f000 -c 483 -m 0x800 -x none -F -o
output/images/rootfs.ubifs
$ ubinize -o output/images/rootfs.ubi -m 0x800 -p 0x20000 -s 512 -O 2048
ubinize.cfg

My .cfg file is:-

[ubifs]
mode=ubi
vol_id=0
vol_type=dynamic
vol_name=rootfs
vol_alignment=1
vol_flags=autoresize
vol_size=61MiB
image=output/images/rootfs.ubifs

And the resulting image is:-

-rw-rw-r-- 1 mpfj mpfj 9437184 Apr 16 10:19 rootfs.ubi

This is then written to a freshly erased 64MB NAND partition, and
appears to mount correctly, apart from the warning about not enough
reserved PEBs, as follows:-

...
[    0.792456] UBI: attaching mtd7 to ubi0
[    1.540858] UBI: scanning is finished
[    1.557578] UBI warning: print_rsvd_warning: cannot reserve enough
PEBs for bad PEB handling, reserved 4, need 40
[    1.561346] UBI: attached mtd7 (name "rootfs", size 64 MiB) to ubi0
[    1.561404] UBI: PEB size: 131072 bytes (128 KiB), LEB size: 126976 bytes
[    1.561434] UBI: min./max. I/O unit sizes: 2048/2048, sub-page size 512
[    1.561464] UBI: VID header offset: 2048 (aligned 2048), data offset:
4096
[    1.561493] UBI: good PEBs: 512, bad PEBs: 0, corrupted PEBs: 0
[    1.561520] UBI: user volume: 1, internal volumes: 1, max. volumes
count: 128
[    1.561554] UBI: max/mean erase counter: 2/1, WL threshold: 4096,
image sequence number: 1434266085
[    1.561591] UBI: available PEBs: 0, total reserved PEBs: 512, PEBs
reserved for bad PEB handling: 4
[    1.562374] UBI: background thread "ubi_bgt0d" started, PID 598
...

I think I've calculated the various option values correctly for
mkfs.ubifs and ubinize.

But since I'm getting the warning, can anyone explain where I've gone
wrong ?

Thanks in advance
Mark J.