1.17. UBI/UBIFS support¶
barebox has both UBI and UBIFS support. For handling UBI barebox has commands similar to the Linux commands ubiformat - format an ubi volume, ubiattach - attach mtd device to UBI, ubidetach - detach an UBI device, ubimkvol - create an UBI volume and ubirmvol - delete an UBI volume.
The first step for preparing a pristine Flash for UBI is to ubiformat - format an ubi volume the device:
If you intend to use a device with UBI you should always use
ubiformat instead of plain
erase - erase flash memory.
ubiformat will make sure the erasecounters are preserved and also
UBI Fastmap won’t work when a flash is erased with
NOTE: when using the UBI Fastmap feature make sure that the UBI is attached and detached
once after using
ubiformat. This makes sure the Fastmap is written.
After a device has been formatted it can be attached with ubiattach - attach mtd device to UBI.
This will create the controlling node
/dev/nand0.root.ubi and also register all volumes
present on the device as
/dev/nand0.root.ubi.<volname>. When freshly formatted there won’t
be any volumes present. A volume can be created with:
ubimkvol /dev/nand0.root.ubi root 0
The first parameter is the controlling node. The second parameter is the name of the volume.
In this case the volume can be found under
/dev/dev/nand0.root.ubi.root. The third
parameter contains the size. A size of zero means that all available space shall be used.
The next step is to write a UBIFS image to the volume. The image must be created on a host using
mkfs.ubifs requires several arguments for describing the
flash layout. Values for these arguments can be retrieved from a
devinfo ubi under barebox:
barebox@Phytec pcm970:/ devinfo nand0.root.ubi Parameters: peb_size: 16384 leb_size: 15360 vid_header_offset: 512 min_io_size: 512 sub_page_size: 512 good_peb_count: 3796 bad_peb_count: 4 max_erase_counter: 0 mean_erase_counter: 0 available_pebs: 3713 reserved_pebs: 83
To build a UBIFS image for this device the following command is suitable:
mkfs.ubifs --min-io-size=512 --leb-size=15360 --max-leb-cnt=4096 -r rootdir \ /tftpboot/root.ubifs
--max-leb-cnt parameter specifies the maximum number of logical erase blocks
the UBIFS image can ever have. For this particular device a number of 3713 would be
enough. If the image shall be used for multiple boards the maximim peb count of all
boards must be used.
The UBIFS image can be transferred to the board for example with TFTP:
cp /mnt/tftp/root.ubifs /dev/nand0.root.ubi.root
Finally it can be mounted using the mount - mount a filesystem or list mounted filesystems command:
The default mount path when the mount point is skipped is
so in this example it will be
The second time the UBIFS is mounted the above can be simplified to:
ubiattach /dev/nand0.root mount /dev/nand0.root.ubi.root
Mounting the UBIFS can also be made transparent with the automount command.
automount -d /mnt/nand0.root.ubi.root 'mount nand0.root.ubi.root'
will automatically attach the UBI device and mount the UBIFS image to
is first accessed. The automount command can be added to
execute it during startup.
1.17.1. UBI Fastmap¶
When attaching UBI to a flash device the UBI code has to scan all eraseblocks on the
flash. Since this can take some time the Fastmap feature has been introduced. It has
been merged in Linux 3.7. barebox has support for the Fastmap feature, but to use
it some care must be taken. The Fastmap feature reduces scanning time by adding
informations to one of the first blocks of a flash. For technical details see
http://www.linux-mtd.infradead.org/doc/ubi.html#L_fastmap. Since the Fastmap can
only live near the beginning of a flash the Fastmap code relies on finding a free
eraseblock there. The above example command make that sure, but Fastmap is incompatible
with creating a UBI image on a host and directly flashing the UBI image to the
raw NAND/NOR device. In this case the Fastmap code will not find a free eraseblock
and the following message will occur during
UBI error: ubi_update_fastmap: could not find any anchor PEB UBI warning: ubi_update_fastmap: Unable to write new fastmap, err=-28
The Fastmap is first written after a
ubidetach, so it’s important to attach/detach
a UBI volume after using