Create a FLASH partition to store user's HOME

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


APF9328 APF27 APF51 APF28
* 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 partitioning:
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 partitioning 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:
U-Boot 201x.xx U-Boot 1.3.4
BIOS> nand erase.part user                              
(which now starts at (rootfs_offset + rootfs_len) = 0x0ce80000
BIOS> nand erase 0x0ce80000
* Check your NAND FLASH size:
BIOS> reset
U-Boot 2013.04 (...

NAND:  512 MiB
...
  • So here we have 512 MBytes. Then check current partitioning:
BIOS> printenv mtdparts
mtdparts=mtdparts=mxc_nand:1M(u-boot)ro,512K(env),512K(env2),1M(firmware),512K(dtb),512K(splash),8M(kernel),-(rootfs)
  • Here we have the default APF51 partitioning scheme (rootfs of 500 MBytes). Now I will reduce rootfs size to 450 MBytes (0x1c200000 in hexa) and so have the remaining (50 MBytes) for my "user" partition:
BIOS> setenv mtdparts 'mtdparts=mxc_nand:1M(u-boot)ro,512K(env),512K(env2),1M(firmware)
,512K(dtb),512K(splash),8M(kernel),450M(rootfs),-(user)'
BIOS> setenv addubifsargs 'setenv bootargs ${bootargs} ubi.mtd=rootfs ubi.mtd=user root=ubi0:rootfs rootfstype=ubifs'
BIOS> nand erase.part user

NAND erase.part: device 0 offset 0x1ce00000, size 0x3200000
OK
  • Save your changes, update the rootfs partition (U-Boot 201x.xx) and boot Linux:
BIOS> saveenv
BIOS> run update_rootfs
BIOS> boot

Linux

  • In Linux boot message you should see your newly created partition is detected:
Boards with U-Boot 1.3.4 (offset may vary) Boards with U-Boot >= 2013.xx (offset may vary)
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"
9 cmdlinepart partitions found on MTD device mxc_nand
Creating 9 MTD partitions on "mxc_nand":
0x000000000000-0x000000100000 : "u-boot"
0x000000100000-0x000000180000 : "env"
0x000000180000-0x000000200000 : "env2"
0x000000200000-0x000000300000 : "firmware"
0x000000300000-0x000000380000 : "dtb"
0x000000380000-0x000000400000 : "splash"
0x000000400000-0x000000c00000 : "kernel"
0x000000c00000-0x00001ce00000 : "rootfs"
0x00001ce00000-0x000020000000 : "user"
  • you can also see it in /proc/mtd:
Example for APF28 with U-Boot 2012.02 Example for APF51 with U-Boot 2013.04
# cat /proc/mtd 
dev:    size   erasesize  name
mtd0: 00300000 00020000 "u-boot"
mtd1: 00080000 00020000 "env"
mtd2: 00080000 00020000 "env2"
mtd3: 00080000 00020000 "dtb"
mtd4: 00080000 00020000 "splash"
mtd5: 00800000 00020000 "kernel"
mtd6: 1c200000 00020000 "rootfs"
mtd7: 03200000 00020000 "user"
# cat /proc/mtd 
dev:    size   erasesize  name
mtd0: 00100000 00020000 "u-boot"
mtd1: 00080000 00020000 "env"
mtd2: 00080000 00020000 "env2"
mtd3: 00100000 00020000 "firmware"
mtd4: 00080000 00020000 "dtb"
mtd5: 00080000 00020000 "splash"
mtd6: 00800000 00020000 "kernel"
mtd7: 1c200000 00020000 "rootfs"
mtd8: 03200000 00020000 "user"
  • From now on, please note the MTD number of your user partition. In previous table it was 7 on APF28 and 8 on APF51. Then define it in shell:
# export MTD_ID=8        (for example on APF51 with U-Boot >= 2013.04)
  • Check a device node was created for your new partition:
# ls -al /dev/mtdblock$MTD_ID
brw-rw----    1 root     disk       31,   8 Jan  1 00:00 /dev/mtdblock8
  • Now it's time to format your new user partition (preferably with UBIFS on new boards/BSP versions):
UBIFS JFFS2
* For UBIFS, create a temporary mount point, format and mount the partition:
# mkdir /tmp/nand
# ubidetach -m $MTD_ID
# ubiformat /dev/mtd$MTD_ID
# ubiattach /dev/ubi_ctrl -m $MTD_ID
# ubimkvol /dev/ubi1 -m -N user
# mount -t ubifs ubi1:user /tmp/nand
# ls /tmp/nand
* For JFFS2, create a temporary mount point and mount the partition. It will be automatically formatted:
# mkdir /tmp/nand
# mount -t jffs2 /dev/mtdblock$MTD_ID /tmp/nand
# ls /tmp/nand/
  • Move your user data to the partition:
# cp -r /root/* /tmp/nand/
# cp -r /root/.[ab]* /tmp/nand/
  • Make it automatically mounted at every boot by adding it to /etc/fstab:
UBIFS JFFS2
# vi /etc/fstab
...
sysfs           /sys           sysfs    defaults               0      0        
usbfs           /proc/bus/usb  usbfs    defaults               0      0
ubi1:user       /root          ubifs    defaults,noatime,rw    0      0      <<------
# vi /etc/fstab
...
sysfs           /sys           sysfs    defaults          0      0        
usbfs           /proc/bus/usb  usbfs    defaults          0      0
/dev/mtdblock7  /root          jffs2    defaults          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 !