How to support UBIFS through MTD

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Purpose

The purpose of this article is to introduce the UBIFS file system:

  • General information
  • Main components
  • How to use UBIFS

Overview

UBI/UBIFS[1] is designed to work on top of raw Flash memories (NOR/NAND). It does not work on top of block devices (MMC/SD cards).
3 subsystems are involved with UBIFS:

  • The UBIFS file system, which works on top of UBI volumes. Please refer to the MTD UBIFS documentation[2].
  • The UBI subsystem, which works on top of MTD devices. This subsystem is a wear-leveling and volume management system for raw Flash memories. Please refer to the MTD UBI documentation[3].
  • The MTD subsystem, which provides uniform interfaces to access raw Flash memories. Please refer to the MTD framework.

Kernel configuration

UBIFS is activated by default in ST deliveries. Nevertheless, if a specific configuration is needed, this section indicates how UBIFS can be activated/deactivated in the kernel.

Activate UBIFS in the kernel configuration with the Linux Menuconfig tool: Menuconfig or how to configure kernel. 

[*] Device Drivers --->
    <*> Memory Technology Device (MTD) support --->
        <*> Enable UBI- Unsorted block images --->
File systems --->
    [*] Miscellaneous filesystems --->
        <*> UBIFS file system support

Using a UBIFS partition as root file system

Assuming the UBIFS image is already flashed to the raw Flash memory, the user has to provide:

  • The boot arguments to attach the UBI device (using ubi.mtd=X), where X is the MTD device which hosts the root file system volume, named "rootfs".
  • The file system type (using rootfstype=ubifs).
  • The UBI volume that has to be mounted (using root=ubiX_T or root=ubiX:NAME), where X is the UBI device number, Y is the UBI volume number and NAME is the UBI volume name.


Please refer to the NAND memory mapping to check the "rootfs" location in ST deliveries.
The following is an example of the kernel boot arguments assuming that the rootfs has been flashed on MTD partition 3 (/dev/mtd3) and this MTD partition has an UBI volume named "rootfs". In this case, the kernel command-line[4] will be: 

 ubi.mtd=3 root=ubi0:rootfs rootfstype=ubifs rootwait rw console=ttySTM0,115200

Mounting a UBIFS partition

Assuming that the "userfs" volume has been flashed on MTD partition 3 (/dev/mtd3), below steps show how to mount this volume.
Please refer to the NAND memory mapping to check the "userfs" location in ST deliveries.

  • Attach mtd3 to UBI.
 Board $> ubiattach /dev/ubi_ctrl -m 3
 ubi0: attaching mtd3
 ubi0: scanning is finished
 ubi0: attached mtd3 (name "UBI", size 1018 MiB)
 ubi0: PEB size: 262144 bytes (256 KiB), LEB size: 253952 bytes
 ubi0: min./max. I/O unit sizes: 4096/4096, sub-page size 4096
 ubi0: VID header offset: 4096 (aligned 4096), data offset: 8192
 ubi0: good PEBs: 4068, bad PEBs: 4, corrupted PEBs: 0
 ubi0: user volume: 4, internal volumes: 1, max. volumes count: 128
 ubi0: max/mean erase counter: 2/0, WL threshold: 4096, image sequence number: 980643132
 ubi0: available PEBs: 0, total reserved PEBs: 4068, PEBs reserved for bad PEB handling: 76
 ubi0: background thread "ubi_bgt0d" started, PID 1138
 UBI device number 0, total 4068 LEBs (1033076736 bytes, 985.2 MiB), available 0 LEBs (0 bytes), LEB size 253952 bytes (248.0 KiB)
  • Mount "userfs" volume.
 Board $> mount -t ubifs ubi0:userfs /media
 UBIFS (ubi0:3): background thread "ubifs_bgt0_3" started, PID 648
 UBIFS (ubi0:3): UBIFS: mounted UBI device 0, volume 3, name "userfs"
 UBIFS (ubi0:3): LEB size: 253952 bytes (248 KiB), min./max. I/O unit sizes: 4096 bytes/4096 bytes
 UBIFS (ubi0:3): FS size: 138911744 bytes (132 MiB, 547 LEBs), journal size 9404416 bytes (8 MiB, 38 LEBs)
 UBIFS (ubi0:3): reserved for root: 0 bytes (0 KiB)
 UBIFS (ubi0:3): media format: w4/r0 (latest is w5/r0), UUID 6A93917C-50A2-4498-B372-6F8646F5257D, small LPT model
  • Check "userfs" volume is mounted.
 Board $> mount | grep ubifs
 ubi0:userfs on /media type ubifs (rw,relatime,assert=read-only,ubi=0,vol=3)

Create a default file system on a MTD partition

  • Format a MTD partition (mtd3 will be used in this example).
 Board $> ubiformat /dev/mtd3
 ubiformat: mtd3 (nand), size 1067450368 bytes (1018.0 MiB), 4072 eraseblocks of 262144 bytes (256.0 KiB), min. I/O size 4096 bytes
 libscan: scanning eraseblock 4071 -- 100 % complete
 ubiformat: 4068 eraseblocks have valid erase counter, mean value is 1
 ubiformat: 4 bad eraseblocks found, numbers: 4068, 4069, 4070, 4071
 ubiformat: formatting eraseblock 4071 -- 100 % complete
  • Attach mtd3 to UBI subsytem.
 Board $> ubiattach /dev/ubi_ctrl -m 3
 ubi0: attaching mtd3
 ubi0: scanning is finished
 ubi0: attached mtd3 (name "UBI", size 1018 MiB)
 ubi0: PEB size: 262144 bytes (256 KiB), LEB size: 253952 bytes
 ubi0: min./max. I/O unit sizes: 4096/4096, sub-page size 4096
 ubi0: VID header offset: 4096 (aligned 4096), data offset: 8192
 ubi0: good PEBs: 4068, bad PEBs: 4, corrupted PEBs: 0
 ubi0: user volume: 0, internal volumes: 1, max. volumes count: 128
 ubi0: max/mean erase counter: 4/2, WL threshold: 4096, image sequence number: 1744321690
 ubi0: available PEBs: 3988, total reserved PEBs: 80, PEBs reserved for bad PEB handling: 76
 ubi0: background thread "ubi_bgt0d" started, PID 613
 UBI device number 0, total 4068 LEBs (1033076736 bytes, 985.2 MiB), available 3988 LEBs (1012760576 bytes, 965.8 MiB), LEB size 253952 bytes (248.0 Ki)
  • Check the UBI status.
 Board $> ubinfo --all
 UBI version:                    1
 Count of UBI devices:           1
 UBI control device major/minor: 10:57
 Present UBI devices:            ubi0
 
 ubi0
 Volumes count:                           0
 Logical eraseblock size:                 253952 bytes, 248.0 KiB
 Total amount of logical eraseblocks:     4068 (1033076736 bytes, 985.2 MiB)
 Amount of available logical eraseblocks: 3988 (1012760576 bytes, 965.8 MiB)
 Maximum count of volumes                 128
 Count of bad physical eraseblocks:       4
 Count of reserved physical eraseblocks:  76
 Current maximum erase counter value:     6
 Minimum input/output unit size:          4096 bytes
 Character device major/minor:            240:0
  • Create a UBI volume named "testfs" related to our partition.
 Board $> ubimkvol /dev/ubi0 -N testfs -m
 Set volume size to 1012760576
 Volume ID 0, size 3988 LEBs (1012760576 bytes, 965.8 MiB), LEB size 253952 bytes (248.0 KiB), dynamic, name "testfs", alignment 1
  • Mount "testfs".
 Board $> mount -t ubifs ubi0:testfs /media
 UBIFS (ubi0:0): default file-system created
 UBIFS (ubi0:0): background thread "ubifs_bgt0_0" started, PID 763
 UBIFS (ubi0:0): UBIFS: mounted UBI device 0, volume 0, name "testfs"
 UBIFS (ubi0:0): LEB size: 253952 bytes (248 KiB), min./max. I/O unit sizes: 4096 bytes/4096 bytes
 UBIFS (ubi0:0): FS size: 1009205248 bytes (962 MiB, 3974 LEBs), journal size 33521664 bytes (31 MiB, 132 LEBs)
 UBIFS (ubi0:0): reserved for root: 4952683 bytes (4836 KiB)
 UBIFS (ubi0:0): media format: w5/r0 (latest is w5/r0), UUID 66AD8600-A3F4-4EF7-9821-0FE87D7C3DA0, small LPT model
  • Check that the file system is empty.
 Board $> ls -l /media
 total 0
  • Create a random data file.
 Board $> dd if=/dev/urandom of=/tmp/random.hex bs=1M count=10
 10+0 records in
 10+0 records out
 10485760 bytes (10 MB, 10 MiB) copied, 0.667978 s, 15.7 MB/s
 Board $> sync
  • Copy the random data file in /media.
 Board $> cp /tmp/random.hex /media/
 Board $> sync
  • Un-mount /media.
 Board $> umount /media
 UBIFS (ubi0:0): un-mount UBI device 0
 UBIFS (ubi0:0): background thread "ubifs_bgt0_0" stops
  • Mount "testfs".
 Board $> mount -t ubifs ubi0:testfs /media
 UBIFS (ubi0:0): background thread "ubifs_bgt0_0" started, PID 800
 UBIFS (ubi0:0): UBIFS: mounted UBI device 0, volume 0, name "testfs"
 UBIFS (ubi0:0): LEB size: 253952 bytes (248 KiB), min./max. I/O unit sizes: 4096 bytes/4096 bytes
 UBIFS (ubi0:0): FS size: 1009205248 bytes (962 MiB, 3974 LEBs), journal size 33521664 bytes (31 MiB, 132 LEBs)
 UBIFS (ubi0:0): reserved for root: 4952683 bytes (4836 KiB)
 UBIFS (ubi0:0): media format: w5/r0 (latest is w5/r0), UUID 66AD8600-A3F4-4EF7-9821-0FE87D7C3DA0, small LPT model
  • Check that the random data file created is identical in /tmp and /media.
 Board $> md5sum /tmp/random.hex /media/random.hex
 a7e4a0b65560e917805944ca04fc9695  /tmp/random.hex
 a7e4a0b65560e917805944ca04fc9695  /media/random.hex
  • Un-mount /media.
 Board $> umount /media
 UBIFS (ubi0:0): un-mount UBI device 0
 UBIFS (ubi0:0): background thread "ubifs_bgt0_0" stops
  • Detach mtd3.
 Board $> ubidetach -m 3
 ubi0: detaching mtd3
 ubi0: mtd3 is detached

References

Please refer to the following links for full description:

  1. ↑ Documentation/filesystems/ubifs.txt | |}} UBIFS
  2. ↑ MTD UBIFS
  3. ↑ MTD UBI
  4. ↑ Documentation/admin-guide/kernel-parameters.rst | |}} The kernel's command-line parameters

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