The Unsorted Block Image File System (UBIFS) is designed to operate on raw flash devices. It was first introduced into the 2.6.27 Linux Kernel in October 2008.
UBIFS works on an Unsorted Block Image (UBI) device which provides tracking of bad flash blocks and wear leveling. UBI works on top of MTD.
For further information see :
Before we can start building UBIFS and UBI images, we need to know details of the flash device fitted on the GuruPlug. This can be achieved by running mtdinfo -a on our target device, i.e. the GuruPlug.
Pay particular attention to the Eraseblock size, Sub-page size, Minimum input/output unit size and the number of eraseblocks for the partition where our UBIFS will reside.
# mtdinfo -a Count of MTD devices: 3 Present MTD devices: mtd0, mtd1, mtd2 Sysfs interface supported: yes mtd0 Name: u-boot Type: nand Eraseblock size: 131072 bytes, 128.0 KiB Amount of eraseblocks: 8 (1048576 bytes, 1024.0 KiB) Minimum input/output unit size: 2048 bytes Sub-page size: 512 bytes OOB size: 64 bytes Character device major/minor: 90:0 Bad blocks are allowed: true Device is writable: true mtd1 Name: uImage Type: nand Eraseblock size: 131072 bytes, 128.0 KiB Amount of eraseblocks: 32 (4194304 bytes, 4.0 MiB) Minimum input/output unit size: 2048 bytes Sub-page size: 512 bytes OOB size: 64 bytes Character device major/minor: 90:2 Bad blocks are allowed: true Device is writable: true mtd2 Name: root Type: nand Eraseblock size: 131072 bytes, 128.0 KiB Amount of eraseblocks: 4056 (531628032 bytes, 507.0 MiB) Minimum input/output unit size: 2048 bytes Sub-page size: 512 bytes OOB size: 64 bytes Character device major/minor: 90:4 Bad blocks are allowed: true Device is writable: true
Make a ZLIB compressed (-x zlib) UBI filesystem image with a minimum I/O unit size of 2048 bytes (-m 2048), a logical erase block (LEB) size of 129024 bytes and a maximum logical erase block count of 4056:
# mkfs.ubifs -v -x zlib -m 2048 -e 129024 -c 4056 -r rootfs-f12/ rootfs.ubifs.img mkfs.ubifs root: rootfs-f12/ min_io_size: 2048 leb_size: 129024 max_leb_cnt: 4056 output: rootfs.ubifs.img jrn_size: 8388608 reserved: 0 compr: zlib keyhash: r5 fanout: 8 orph_lebs: 1 space_fixup: 0 super lebs: 1 master lebs: 2 log_lebs: 5 lpt_lebs: 2 orph_lebs: 1 main_lebs: 1132 gc lebs: 1 index lebs: 26 leb_cnt: 1143 UUID: 0CE735AE-7BD5-4CE8-A326-8CF8308A133F Success!
Next, we build an UBI image containing the above filesystem as one volume. Create a configuration file called ubi.cfg containing the following :
[ubifs] mode=ubi image=rootfs.ubifs.img vol_id=0 vol_size=400MiB vol_type=dynamic vol_name=rootfs vol_flags=autoresize
# ubinize -v -o rootfs.ubi.img -m 2048 -p 128KiB -s 512 -O 512 ubi.cfg ubinize: LEB size: 129024 ubinize: PEB size: 131072 ubinize: min. I/O size: 2048 ubinize: sub-page size: 512 ubinize: VID offset: 512 ubinize: data offset: 2048 ubinize: UBI image sequence number: 2057591195 ubinize: loaded the ini-file "ubi.cfg" ubinize: count of sections: 1 ubinize: parsing section "ubifs" ubinize: mode=ubi, keep parsing ubinize: volume type: dynamic ubinize: volume ID: 0 ubinize: volume size: 419430400 bytes ubinize: volume name: rootfs ubinize: volume alignment: 1 ubinize: autoresize flags found ubinize: adding volume 0 ubinize: writing volume 0 ubinize: image file: rootfs.ubifs.img ubinize: writing layout volume ubinize: done
It is advisable not to use nandwrite to flash an UBI image. For more information, see here.
The recommended method is to use ubiformat as this not only preserves the erase counters used for wear leveling, it prevents ECC errors on some NAND flash devices.
ubiformat is not available from the bootloader, thus you need to undertake this task on a bootable GuruPlug. I normally boot using root NFS to carry out this operation.
From the shell on the GuruPlug:
# flash_erase /dev/mtd2 0 0 # ubiformat /dev/mtd2 -s 512 -O 512 -f rootfs.ubi.img
You can test an newly flashed image prior to loading it as the root filesystem (i.e. while using root NFS).
First attach the desired MTD partition to UBI using the ubiattach command. Once this is successful, you can mount the UBIFS.
ubiattach -p /dev/mtd2 mount -t ubifs /dev/ubi0_0 /mnt/ubifs/
Below is the kernel messages of a system booting from the above UBIFS :
NAND device: Manufacturer ID: 0xec, Chip ID: 0xdc (Samsung NAND 512MiB 3,3V 8-bit)
Scanning device for bad blocks
Creating 3 MTD partitions on "orion_nand":
0x000000000000-0x000000100000 : "u-boot"
0x000000100000-0x000000500000 : "uImage"
0x000000500000-0x000020000000 : "root"
UBI: attaching mtd2 to ubi0
UBI: physical eraseblock size: 131072 bytes (128 KiB)
UBI: logical eraseblock size: 129024 bytes
UBI: smallest flash I/O unit: 2048
UBI: sub-page size: 512
UBI: VID header offset: 512 (aligned 512)
UBI: data offset: 2048
UBI: max. sequence number: 0
UBI: volume 0 ("rootfs") re-sized from 3251 to 4012 LEBs
UBI: attached mtd2 to ubi0
UBI: MTD device name: "root"
UBI: MTD device size: 507 MiB
UBI: number of good PEBs: 4056
UBI: number of bad PEBs: 0
UBI: number of corrupted PEBs: 0
UBI: max. allowed volumes: 128
UBI: wear-leveling threshold: 4096
UBI: number of internal volumes: 1
UBI: number of user volumes: 1
UBI: available PEBs: 0
UBI: total number of reserved PEBs: 4056
UBI: number of PEBs reserved for bad PEB handling: 40
UBI: max/mean erase counter: 0/0
UBI: image sequence number: 576084514
UBI: background thread "ubi_bgt0d" started, PID 461
...
UBIFS: mounted UBI device 0, volume 0, name "rootfs"
UBIFS: file system size: 516225024 bytes (504126 KiB, 492 MiB, 4001 LEBs)
UBIFS: journal size: 9033728 bytes (8822 KiB, 8 MiB, 71 LEBs)
UBIFS: media format: w4/r0 (latest is w4/r0)
UBIFS: default compressor: zlib
UBIFS: reserved for root: 0 bytes (0 KiB)
VFS: Mounted root (ubifs filesystem) on device 0:13.