UBI/UBIFS Filesystem
Overview
On DHCOM Systems with Linux the UBIFS Filesystem is used for the NAND-Flash root-filesystem. The Unsorted Block Image File System (UBIFS) is a filesystem for use with raw flash memory media. UBIFS works on top of an Unsorted Block Images (UBI) device, which is itself on top of an MTD device.
For further details please have a look at
Create Images
To create UBI-Images or UBIFS-Images you need to install the "mtd-utils" on your Linux host pc. We recommend to download the latest version of the mtd-utils form the mtd-utils git-repository because it is reported that some versions from the distribution repositorys are buggy and/or out of date.
Create UBIFS Images
To create a UBIFS Image you need some hardware-depended information.
<min io size>Equals the page-size of the used NAND-Flash<LEB size>Logical Erase Block size<Erase Blocks count>maximum logical erase block count
If got this information, you can create a UBIFS-Image from a directory-tree with the following command:
# sodu mkfs.ubifs -F -r </path/to/your/rootfs/tree> -m <min io size> -e <LEB size> -c <Erase Blocks count> -o </path/to/output/Image.ubifs>
Examples
for am3517 with 256MB NAND-Flash
# sudo mkfs.ubifs –F -r /work/rootfs -m 2048 -e 126976 -c 1700 -o am35x.ubifs
for i.MX25 with 256MB NAND-Flash
# sudo mkfs.ubifs –F -r /work/rootfs -m 2048 -e 129024 -c 1700 -o imx25.ubifs
Remark To use the option -F you habe to run a kernel version 3.0 or higher. You need to have the "mtd-utils" version 1.5.x or higher, too.
Use the ubinfo command on your device to check the LEB size and count.
Example: # ubinfo /dev/ubi0
Create UBI Images
To create a UBI image you have to have already a UBIFS image. Use the following command:
# ubinize -vv -o <output image> -m <min io size> -p <PEB size>KiB -s <subpage-size> -O <VID-hdr-offset> <configuration file>
<min io size>Equals the page-size of the used NAND-Flash<PEB size>Physical Erase Block size (in KiB) - Equals the block size of the NAND-Flash<Erase Blocks count>Count of the available Erase Blocks<subpage-size>Subpage size in bytes. Default value is the minimum input/output size (page-size)<VID-hdr-offset>offset if the VID header from start of the PEB (default is the next min I/O unit or sub-page after the EC header)<configuration file>Path to a configuration file.
Example of a configuration file content (config.ini):
[rootfs_volume]
mode=ubi
image=imx25.ubifs
vol_id=0
vol_type=dynamic
vol_name=nand_rootfs
vol_flags=autoresize
Examples
for am3517
# sudo ubinize -vv -o am3517_rtfs.ubi -m 2048 -p 128KiB config.ini
for i.MX25
# sudo ubinize -vv -o imx25_rtfs.ubi -m 2048 -p 128KiB -s 512 -O 512 config.ini
User-space tools
The UBI/UBIFS user-space tools are included within the mtd-utils.
some commands are:
ubinfo- provides information about UBI devices and volumes found in the system;ubiattach- attaches MTD devices (which describe raw flash) to UBI and creates corresponding UBI devices;ubidetach- detaches MTD devices from UBI devices (the opposite to what ubiattach does);ubimkvol- creates UBI volumes on UBI devices;ubirmvol- removes UBI volumes from UBI devices;ubiupdatevol- updates UBI volumes;ubiformat- formats empty flash, erases flash and preserves erase counters, flashes UBI images to MTD devices;mtdinfo- reports information about MTD devices found in the system.
Use the "-h" option to get more information about the commands.
Flashing UBI/UBIFS Images
The following commands can be used to flash UBI/UBIFS Images on a running linux device (you can not flash your active root filesystem). When you want to run a linux root-filesystem update please use the subfunction Root Filesystem Update of the DHCOM Update Mechnism. In special cases you can use the following commands:
Flash a UBIFS Image
ubiformat /dev/mtdX
ubiattach -m X -d Y /dev/ubi_ctrl
ubimkvol /dev/ubiY -N volume_name -s -m
ubiupdatevol /dev/ubiY_0 /path/to/Image.ubifs
Flash a UBI Image
ubiformat /dev/mtdX –f Image.ubi
Check the health of the NAND-flash
If an UBI Device is used on top of NAND-flash, you can use ubinfo /dev/ubiY to check the health of the NAND-flash.
Here an example:
root@dhcom1bimx6ull:~# ubinfo /dev/ubi0 ubi0 Volumes count: 2 Logical eraseblock size: 126976 bytes, 124.0 KiB Total amount of logical eraseblocks: 1019 (129388544 bytes, 123.3 MiB) Amount of available logical eraseblocks: 0 (0 bytes) Maximum count of volumes 128 Count of bad physical eraseblocks: 5 Count of reserved physical eraseblocks: 15 Current maximum erase counter value: 40 Minimum input/output unit size: 2048 bytes Character device major/minor: 242:0 Present volumes: 0, 1
Important are the following fields:
- "Count of bad physical eraseblocks": This value indicates how many eraseblocks are bad. Note that there may be some eraseblocks that are bad when the NAND-flash memory was manufactured.
- "Count of reserved physical eraseblocks": This number indicates how many eraseblocks are available as a reserve if other eraseblock gets bad. If this reserve is depleted then it is a sign that the NAND-flash is at the end of its life.
- "Current maximum erase counter value": This value indicates how often the eraseblock with the highest number of erases was erased. Note that UBI devices use wear leveling to distribute the erases of heavely used eraseblocks to different eraseblocks. The number of erases an eraseblock can usually last until it gets bad depends on the NAND flash itself. Important: The erase counter is saved inside the data structure of the UBI device, so if you erase the NAND flash without using
ubiformatthe current erase counter will get lost and reset to 1!
You can also check the health of the NAND flash at the bootloader (for example when the linux isn't booting anymore). The following commands are needed for doing this:
mtdpartsto get the name of the UBI device (in this example: "main-nand").ubi part main-nandto set the current partition to the UBI device.ubi infoto print the information about the UBI device.
