Create a FLASH partition to store user's HOME

If you ever did some hacking/devt on your APF board and used /root/ to download or install your experiments, I'm sure you got frustrated when it comes the time where you had to reflash the whole rootfs. Indeed, by default, /root/ is located in the same partition as the rootfs image and so everything you did will be overwritten. Well, you can always backup your data on a SD/microSD or through NFS before doing the rootfs flashing, but I think that, like me, you are little bit lazy ;-).

So in this small tutorial I will explain you how to modify the FLASH setup to store your personnal data on a separated partition and so avoid the backup process when updating your rootfs.

Declare partition in U-Boot

Warning: You may loose the content of your current rootfs partition if going further. So be sure to have backuped your data before.

APF27

• Check your NAND FLASH size:

BIOS> nand info

Device 0: NAND 256MiB 1,8V 16-bit, sector size 128 KiB

• So here I have 256MBytes. Then check current partitionning:

BIOS> printenv mtdparts
mtdparts=mtdparts=mxc_nand.0:640k(U-boot)ro,384k(U-boot_env),512k(firmware),5M(kernel),-(rootfs)

• I have the default APF27 partitionning scheme. Now I will reduce rootfs size to 200 MBytes (0x0C800000 in hexa) and so have the remaining (50 MBytes) for my "user" partition:

U-Boot 1.3.4:

BIOS> setenv mtdparts mtdparts=mxc_nand.0:640k(U-boot)ro,384k(U-boot_env),512k(firmware),5M(kernel),200M(rootfs),-(user)
BIOS> printenv mtdparts
mtdparts=mtdparts=mxc_nand.0:640k(U-boot)ro,384k(U-boot_env),512k(firmware),5M(kernel),200M(rootfs),-(user)
BIOS> setenv rootfs_len 0x0C800000

U-Boot 2011.12:

BIOS> setenv mtdparts mtdparts=mxc_nand.0:1M(u-boot)ro,512K(env),512K(env2),512k(firmware),512K(dtb),5M(kernel),200M(rootfs),-(user)
BIOS> setenv addubifsargs 'setenv bootargs ${bootargs} ubi.mtd=rootfs ubi.mtd=user root=ubi0:rootfs rootfstype=ubifs'
BIOS> printenv mtdparts
mtdparts=mtdparts=mxc_nand.0:1M(u-boot)ro,512K(env),512K(env2),512k(firmware),512K(dtb),5M(kernel),200M(rootfs),-(user)

• Erase the created partition (which now starts at (rootfs_offset + rootfs_len) = 0x0CE80000: (U-Boot 1.3.4)

U-Boot 1.3.4:

BIOS> nand erase 0x0CE80000

U-Boot 2011.12:

BIOS> nand erase.part user

• Save your changes, update the rootfs partition (U-Boot 2011.12) and boot Linux:

BIOS> saveenv
BIOS> run update_rootfs
BIOS> boot

APF9328/APF51/APF28

TODO

Linux

• In Linux boot message you should see you newly created partition detected (U-Boot 1.3.4):

6 cmdlinepart partitions found on MTD device mxc_nand.0                                                                                                                             
Creating 6 MTD partitions on "mxc_nand.0":                                                                                                                                          
0x000000000000-0x0000000a0000 : "U-boot"                                                                                                                                            
0x0000000a0000-0x000000100000 : "U-boot_env"                                                                                                                                        
0x000000100000-0x000000180000 : "firmware"                                                                                                                                          
0x000000180000-0x000000680000 : "kernel"                                                                                                                                            
0x000000680000-0x00000ce80000 : "rootfs"                                                                                                                                            
0x00000ce80000-0x000010000000 : "user"

• Check a device node was created for your new partition (U-Boot 1.3.4: /dev/mtdblock5 - U-Boot 2011.12: /dev/mtdblock7):

# ls /dev/mtdblock*
/dev/mtdblock0  /dev/mtdblock2  /dev/mtdblock4
/dev/mtdblock1  /dev/mtdblock3  /dev/mtdblock5

• For JFFS2: create a temporary mount point and mount the partition (U-Boot 1.3.4: /dev/mtdblock5 - U-Boot 2011.12: /dev/mtdblock7). It will be automatically formatted to JFSS2:

# mkdir /tmp/nand
# mount -t jffs2 /dev/mtdblock7 /tmp/nand
# ls /tmp/nand/

• For UBIFS: create a temporary mount point, format and mount the partition (U-Boot 1.3.4: replace mtd7 by mtd5 and '-m 7' by '-m 5'):

# mkdir /tmp/nand
# ubiformat /dev/mtd7
# ubiattach /dev/ubi_ctrl -m 7
# ubimkvol /dev/ubi1 -s 40MiB -N user
# mount -t ubifs ubi1:user /mnt/nand
# ls /tmp/nand/

• Move your user data to the partition:

# cp -r /root/* /tmp/nand/
# cp -r /root/.[ab]* /tmp/nand/

• Makes it automatically mounted at every boot by adding it to /etc/fstab:

JFFS2:

# vi /etc/fstab
...
sysfs           /sys           sysfs    defaults          0      0        
usbfs           /proc/bus/usb  usbfs    defaults          0      0
/dev/mtdblock7  /root          jffs2    defaults          0      0   <<-----------------

UBIFS:

# vi /etc/fstab
...
sysfs           /sys           sysfs    defaults          0      0        
usbfs           /proc/bus/usb  usbfs    defaults          0      0
ubi1:user       /mnt/nand      ubifs    defaults,noatime,rw    0      0   <<-----------------

• Now you're done. Reboot and enjoy ! ;-)

# reboot
...
# df -h
Filesystem                Size      Used Available Use% Mounted on
rootfs                  200.0M     17.8M    182.2M   9% /
/dev/root               200.0M     17.8M    182.2M   9% /
none                     64.0k         0     64.0k   0% /dev
tmpfs                    61.2M     44.0k     61.1M   0% /tmp
>>> /dev/mtdblock7           49.5M      4.0M     45.5M   8% /root <<<
# ls /root/

• Of course if you reflash your rootfs, even if you keep your personnal data, you will have to repeat the /etc/fstab modification step above !