[[PageOutline]]

= 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
 * http://www.linux-mtd.infradead.org/faq/ubifs.html


= FLASH chip geometry =
[=#flashgeometry]
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 the {{{SPL}}}, {{{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}}} (the {{{image}}} env var) and if found will be sourced
 * a flattened device tree blob (dtb) may exist in {{{boot/}}} (named by the automatic env vars {{{fdt_file}}}, {{{fdt_file1}}}, or {{{fdt_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 ==
[=#creatingubi]
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:
1. create a temporary directory for our rootfs and untar your filesystem to it
{{{#!bash
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
2. copy your kernel files (and u-boot bootscript if you have one):
{{{#!bash
mkdir tmp/boot
cp uImage imx6*-gw*.dtb 6x_bootscript-ventana tmp/boot/
}}}
3. create a ubifs image for the 256MB device geometry:
{{{#!bash
mkfs.ubifs -F -m 2048 -e 124KiB -c 1912 -x zlib -o root.ubifs -d tmp
}}}
4. use {{{ubinize}}} to create ubi images for the 256MB device geometry which can be written to a suitable raw NAND devices in U-Boot using {{{nand write}}}:
{{{#!bash
# 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):
1. create a temporary directory for our rootfs and untar your filesystem to it
{{{#!bash
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
2. copy your kernel files (and u-boot bootscript if you have one):
{{{#!bash
mkdir tmp/boot
cp uImage imx6*-gw*.dtb 6x_bootscript-ventana tmp/boot/
}}}
3. create ubifs images for the 'large' device geometry:
{{{#!bash
mkfs.ubifs -F -m 4096 -e 248KiB -c 8124 -x zlib -o root.ubifs -d tmp
}}}
4. 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:
{{{#!bash
# for the small layout device
cat <<EOF > ubinize.cfg
[ubifs]
mode=ubi
image=root.ubifs #generate this image with mkfs.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) ==
[=#ubiinlinux]
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:
 * [#ubiondevhost use the nandsim kernel module to simulate a NAND device]
 * [#ubiontarget 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 [#creatingubi 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 ===
[=#ubiondevhost]
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:
1. load {{{nandsim}}} module with parameters for specific flash device simulating:
 * 256MB FLASH (what we refer to as the 'normal' flash device):
{{{#!bash
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):
{{{#!bash
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 to {{{nandsim}}} to tell it to use a file-backed storage instead. You can remove the file once you {{{rmmod nandsim}}}.
1. populate NAND with an existing ubi:
{{{#!bash
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.
1. attach the UBI
{{{#!bash
sudo modprobe ubi
sudo ubiattach /dev/ubi_ctrl -m0 -O2048
sudo ubiinfo -a # optionally show info about the UBI
}}}
1. mount the ubifs to host
{{{#!bash
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:
{{{#!bash
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:
{{{#!bash
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:
{{{#!bash
sudo rmmod nandsim
}}}

References:
 * http://www.linux-mtd.infradead.org/faq/nand.html#L_nand_nandsim


=== On a target board with NAND FLASH ===
[=#ubiontarget]
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 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}}}):
{{{#!bash
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:
{{{#!bash
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 image
{{{#!bash
ubidetach /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 tarball
{{{#!bash
ubidetach /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
}}}
Troubleshooting:

The output beneath indicates that /dev/mtd2 is not attached and you may proceed with manipulating the NAND flash.
{{{#!bash
root@OpenWrt:/# ubidetach /dev/ubi_ctrl -m 2
ubidetach: error!: cannot detach mtd2
           error 16 (Resource busy)
}}}

== Working with UBI in U-boot Bootloader ==
[=#ubiinuboot]
The U-boot bootloader used by Ventana has support for ubi:
 * mounting a ubi
 * removing ubi volumes
 * creating ubi volumes
 * writing ubi volumes

[=#BasicMethod]
=== Updating NAND FLASH with a UBI image ===
If your ubi image is on a [wiki:tftpserver 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):
{{{#!bash
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 the {{{image_rootfs}}} env variable such that you could do a {{{setenv 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:
{{{#!bash
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:
{{{#!bash
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:
{{{#!bash
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'''


[=#uboot-ubifs]
=== Updating NAND FLASH with a ubifs image ===
To update the contents of a ubi with a ubifs in U-Boot:
{{{#!bash
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.

=== Creating your own .ubifs file
{{{#!bash
sudo mkfs.ubifs -d /your/rootfs/ -F -m 4096 -e 248KiB -c 8124 -x zlib -o A_large.ubifs
}}}

Essentials:

 * **-r** Build file system from directory DIR
 * **-F**  The -F option causes mkfs.ubifs to set a special flag in the superblock, which triggers a "free space fixup" procedure in the kernel the very first time the filesystem is mounted. This fixup procedure involves finding all empty pages in the UBIFS file system and re-erasing them. This ensures that NAND pages which contain all 0xFF data get fully erased, which removes any problematic non-0xFF data from their OOB areas.
 * **-m**  Minimum I/O unit size
 * **-e**  Logical erase block size
 * **-c** Maximum logical erase block count
 * **-x** Compression type - "lzo", "favor_lzo", "zlib" or "none" (default: "lzo")
 * **-o** Output to FILENAME
 * **-h** Help, provides full list of options