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Unsorted Block Images (UBI)
Unsorted block images (UBI) is an erase block management layer for flash memory devices such as raw NAND devices. UBI serves two purposes:
- tracking NAND flash bad blocks
- providing wear leveling
UBI was written specifically for UBIFS so that the filesystem does not have to deal with these issues. UBIFS is a successor to JFFS2 and a competitor to LogFS.
References:
- http://en.wikipedia.org/wiki/UBIFS#Unsorted_Block_Images
- http://www.linux-mtd.infradead.org/faq/ubi.html
FLASH chip geometry
Because UBI takes care of bad block tracking and wear leveling, it needs to know some details about the geometry of the raw FLASH device when creating an image.
The geometry data can be found in the datasheet for the specific flash device used. Gateworks uses two different sized devices which do not share geometries.
UBI use on Gateworks Ventana
UBI is used on the Gateworks Ventana for raw NAND storage. Prior Gateworks product families typically JFFS2.
The Gateworks Ventana default U-Boot environment scripts make a few assumptions about booting from NAND flash:
- the
mtdparts
env var partitions the NAND device into sections for uboot (16MB as this accounts for theSPL
,u-boot.img
and redundancy for bad blocks), u-boot env (1MB), rootfs (the remainder of the device) - the 'rootfs' partition (defined by the
mtdparts
env var) contains a UBI device/image - the UBI device/image in the rootfs partition contains a volume also called 'rootfs'
- an optional bootscript may exist in
boot/6x_bootscript-ventana
(theimage
env var) and if found will be sourced - a flattened device tree blob (dtb) may exist in
boot/
(named by the automatic env varsfdt_file
,fdt_file1
, orfdt_file2
) - a kernel may exist in
boot/uImage
The above assumptions are not requirements - the U-Boot env scripts can be changed to suit your needs.
Creating a UBI using existing rootfs, kernel, and device-tree blobs
To create a UBI image suitable for booting on a standard Gateworks Ventana bootloader (taking into account the assumptions above) you can do the following on a Linux system provided you have a root filesystem (myrootfs.tar.gz
), kernel (uImage
), and device-tree dtb files (imx6*-gw*.dtb
).
256MB FLASH devices
To create a UBI image suitable for the 256MB FLASH devices:
- create a temporary directory for our rootfs and untar your filesystem to it
mkdir tmp fakeroot tar --numeric-owner -xvf myrootfs.tar.gz -C tmp
- Note that
fakeroot
is used because this allows you preserve the ownership of files that you have in your rootfs such as root owned /dev files
- Note that
- copy your kernel files (and u-boot bootscript if you have one):
mkdir tmp/boot cp uImage imx6*-gw*.dtb 6x_bootscript-ventana tmp/boot/
- create a ubifs image for the 256MB device geometry:
mkfs.ubifs -F -m 2048 -e 124KiB -c 1912 -x zlib -o root.ubifs -d tmp
- use
ubinize
to create ubi images for the 256MB device geometry which can be written to a suitable raw NAND devices in U-Boot usingnand write
:# for the small layout device cat <<EOF > ubinize.cfg [ubifs] mode=ubi image=root.ubifs vol_id=0 vol_type=dynamic vol_name=rootfs vol_flags=autoresize EOF ubinize -m 2048 -p 128KiB -s 2048 -o image.ubi ubinize.cfg
1GB or 2GB FLASH devices
To create a UBI image suitable for the 1GB or larger FLASH devices (Note that the parameters to mkfs.ubifs
and ubinize
change):
- create a temporary directory for our rootfs and untar your filesystem to it
mkdir tmp fakeroot tar --numeric-owner -xvf myrootfs.tar.gz -C tmp
- Note that
fakeroot
is used because this allows you preserve the ownership of files that you have in your rootfs such as root owned /dev files
- Note that
- copy your kernel files (and u-boot bootscript if you have one):
mkdir tmp/boot cp uImage imx6*-gw*.dtb 6x_bootscript-ventana tmp/boot/
- create ubifs images for the 'large' device geometry:
mkfs.ubifs -F -m 4096 -e 248KiB -c 8124 -x zlib -o root.ubifs -d tmp
- use
ubinize
to create ubi image for the 'large' device geometry which can be written to a suitable raw NAND devices in U-Boot using nand write:# for the small layout device cat <<EOF > ubinize.cfg [ubifs] mode=ubi image=root.ubifs vol_id=0 vol_type=dynamic vol_name=rootfs vol_flags=autoresize EOF ubinize -m 4096 -p 256KiB -s 4096 -o image.ubi ubinize.cfg
Working with a UBI in Linux OS (extracting or manipulating contents)
Linux has support for ubi:
- mounting a ubi
- creating/renaming/removing ubi volumes
- reading/writing ubi volumes
Working with UBI and UBIFS volumes on Linux require use of the following:
- tools (from
mtd-utils
package):ubiattach
ubidetach
ubiformat
ubirename
ubiupdatevol
ubiinfo
ubimkvol
ubirmvol
- kernel support:
- mtd (the MTD layer)
- mtdblock (the block layer over MTD)
- ubi (ubi support)
- ubifs (ubi filesystem support)
- nandsim (if you want to simulate a NAND device on a development host)
When using the above tools the MTD partition must not be mounted by your Linux OS meaning you either have to:
- use the nandsim kernel module to simulate a NAND device
- boot Linux target with NAND storage using another boot media (ramdisk, usb, mmc, sata, etc)
Note that the creation of ubifs and ubi images is covered in the section above. This section is all about extracting and / or manipulating the contents of a ubi volume.
References:
- http://free-electrons.com/blog/creating-flashing-ubi-ubifs-images/
- http://elinux.org/UBIFS
- http://www.linux-mtd.infradead.org/faq/ubifs.html
On a (NAND-less) Linux Development Host
Often you want to work with UBI and UBIFS images on a Linux Development Host which has no NAND itself. While it is not currently possible to mount a UBI or UBIFS as a loopback device (commonly used for other types of block devices) you can use the nandsim kernel module to simulate a NAND device on a NAND-less Linux development host.
To create a simulated NAND device you need to know the first four bytes returned by the READ_ID flash command, which identifies the characteristics of the device. These values can be found in the datasheet of the FLASH devices. As Gateworks boards support two flash sizes, we will show both examples.
To create a virtual NAND device on a NAND-less Linux development system:
- load
nandsim
module with parameters for specific flash device simulating:- 256MB FLASH (what we refer to as the 'normal' flash device):
sudo rmmod nandsim sudo modprobe nandsim first_id_byte=0x2c \ second_id_byte=0xda \ third_id_byte=0x90 \ fourth_id_byte=0x95
- 1GB or 2GB FLASH (what we refer to as the 'large' flash device):
sudo rmmod nandsim sudo modprobe nandsim \ first_id_byte=0x2c \ second_id_byte=0xd5 \ third_id_byte=0xd1 \ fourth_id_byte=0xa6
- the above create a
/dev/mtd0
device on your development host - by default nandsim will use RAM backed storage which makes for much faster read/write access, however if you are cramped for RAM space and simulating a large device (ie 2GB) you can add a
cache_file=/tmp/nandimage
param tonandsim
to tell it to use a file-backed storage instead. You can remove the file once yourmmod nandsim
.
- 256MB FLASH (what we refer to as the 'normal' flash device):
- populate NAND with an existing ubi:
sudo modprobe mtdblock sudo dd if=image.ubi of=/dev/mtdblock0 bs=2048
- the mtdblock module creates a
/dev/mtdblock0
device on your development host - Note that instead of the dd command above you could also have used
ubiformat /dev/mtd0
to wipe and format a new ubi but this section is documenting how to extract and alter contents of an existing ubi.
- the mtdblock module creates a
- attach the UBI
sudo modprobe ubi sudo ubiattach /dev/ubi_ctrl -m0 -O2048 sudo ubiinfo -a # optionally show info about the UBI
- mount the ubifs to host
sudo modprobe ubifs sudo mkdir /mnt/ubi # create a mountpoint sudo mount -t ubifs ubi0 /mnt/ubi ls /mnt/ubi # optionally list contents of mounted filesystem
Once you are done working with the files in /mnt/ubi
simply unmount the device:
sudo umount /mnt/ubi
If you have altered the filesystem and wish to extract the altered UBI you can detach and use dd to copy it to a file:
sudo ubidetach /dev/ubi_ctrl -m0 sudo dd if=/dev/mtdblock0 of=image-updated.ubi bs=2048
And when you are done working with the simulated NAND device completely, remove the nandsim
module to free up your system memory:
sudo rmmod nandsim
References:
On a target board with NAND FLASH
To extract or manipulate the contents of a UBI within the NAND Flash of a Linux system, Linux must be booted from a secondary medium on a device with NAND FLASH and without the NAND FLASH partition being mounted.
The following examples assume that UBI has been configured to use the 3rd (zero based) MTD FLASH partition (ubi.mtd=2
kernel command line) as we typically use the mtdparts=nand:16m(uboot),1m(env),-(rootfs)
env variable in U-Boot to dynamically modify the Linux Device-Tree to partition the NAND flash device into 3 partitions: bootloader, bootloader-env, and rootfs. Thus the bootloader is /dev/mtd0
, the bootloader env is /dev/mtd1
, and the rootfs is /dev/mtd2
.
Examples:
- Mounting UBI NAND FLASH volume (from
/dev/mtd2
):ubidetach /dev/ubi_ctrl -m 2 # Make sure /dev/mtd2 is not currently attached ubiattach /dev/ubi_ctrl -m 2 # attach /dev/mtd2 as /dev/ubi0 mount -t ubifs ubi0:rootfs /mnt/ubi #mount 'rootfs' volume from /dev/ubi0 to /mnt/ubi
- Updating NAND FLASH using linux target with NAND(
/dev/mtd2
) with a UBI image:ubidetach /dev/ubi_ctrl -m 2 # Make sure /dev/mtd2 is not currently attached sync ubiformat /dev/mtd2 -y -f image.ubi
- Updating NAND FLASH partition (
/dev/mtd2
) with a UBIFS imageubidetach /dev/ubi_ctrl -m 2 # Make sure /dev/mtd2 is not currently attached ubiformat /dev/mtd2 -y # format (will wipe contents!) ubiattach /dev/ubi_ctrl -m 2 # attach /dev/mtd2 as /dev/ubi0 ubimkvol /dev/ubi0 -N rootfs -m # create a volume on /dev/ubi0 named 'rootfs' ubiupdatevol /dev/ubi0_0 image.ubifs
- Updating NAND FLASH partition (
/dev/mtd2
) with a tarballubidetach /dev/ubi_ctrl -m 2 # Make sure /dev/mtd2 is not currently attached ubiformat /dev/mtd2 -y # format (will wipe contents!) ubiattach /dev/ubi_ctrl -m 2 # attach /dev/mtd2 as /dev/ubi0 ubimkvol /dev/ubi0 -N rootfs -m # create a volume on /dev/ubi0 named 'rootfs' mkdir /mnt/ubi # create a mount-point mount -t ubifs ubi0:rootfs /mnt/ubi # mount 'rootfs' volume from /dev/ubi0 to /mnt/ubi tar xvf rootfs.tar.gz -C /mnt/ubi # extract tarball umount /mnt/ubi # unmount filesystem
Working with UBI in U-boot Bootloader
The U-boot bootloader used by Ventana has support for ubi:
- mounting a ubi
- removing ubi volumes
- creating ubi volumes
- writing ubi volumes
Updating NAND FLASH with a UBI image
If your ubi image is on a tftp server as image.ubi
you can use the following to update the 'rootfs' NAND FLASH partition in U-Boot (update the ip addresses as appropriate for your network environment):
setenv ipaddr 192.168.1.1 setenv serverip 192.168.1.254 tftp ${loadaddr} image.ubi && \ nand erase.part rootfs && \ nand write ${loadaddr} rootfs ${filesize}
- Note the
nand_update
script will perform the last step for you using the image name specified in theimage_rootfs
env variable such that you could do asetenv image_rootfs image.ubi; run nand_update
If your ubi image is on the first partition of a FAT formated MMC called image.ubi
you can do the following:
mmc rescan fatload mmc 0:1 ${loadaddr} image.ubi && \ nand erase.part rootfs && \ nand write ${loadaddr} rootfs ${filesize}
If your ubi image is on the first partition of a ext2/3/4 formated MMC called image.ubi
you can do the following:
mmc rescan ext2load mmc 0:1 ${loadaddr} image.ubi && \ nand erase.part rootfs && \ nand write ${loadaddr} rootfs ${filesize}
If your ubi image is on the first partition of a FAT formatted USB stick called image.ubi
you can do the following:
usb start usb dev 0 fatload usb 0:1 ${loadaddr} image.ubi && \ nand erase.part rootfs && \ nand write ${loadaddr} rootfs ${filesize}
Note that operating on the ubi device as described here destroys the wear-leveling information contained in the UBI therefore it is recommended to work at the ubi volume layer to replace ubifs volumes as described below
Updating NAND FLASH with a ubifs image
To update the contents of a ubi with a ubifs in U-Boot:
ubi part rootfs # select the 'rootfs' partition (from mtdparts env var) for ubi ubi info layout # list volumes ubi remove rootfs # remove rootfs volume ubi create rootfs a00000 static # create a 10MB volume named rootfs tftp ${loadaddr} ventana/root.ubifs && ubi write ${loadaddr} rootfs ${filesize} ubifsmount ubi0:rootfs # mount rootfs volume from ubi ubifsls / ubifsumount
Operating on a NAND device at the ubi volume layer like this preserves the wear-leveling information for your flash device and is therefore recommended, especially if you are doing this often.
Use the information in the section above for examples on how to load data in uboot from various sources such as network, mmc, usb.
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nand_split_update.scr
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sourceable uboot script to add the nand_split_update command
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