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How to switch to btrfs

Partition layout

The following table shows the partition layout before and after the switch.

Partition Name Before Before [MiB] Name After After [MiB]
GPT   1   1
mmcblk0p1 u-boot0 2 u-boot0 2
mmcblk0p2 u-boot-env0 1 u-boot-env0 1
mmcblk0p3 u-boot1 2 u-boot1 2
mmcblk0p4 u-boot-env1 1 u-boot-env1 1
mmcblk0p5 factory 1 factory 1
mmcblk0p6 panic 24 panic 24
mmcblk0p7 boot 32 boot 64
mmcblk0p8 rootfs 1536 home 3632
mmcblk0p9 update 768    
mmcblk0p10 home 1360    


Automatic conversion

If you don’t mind loosing the contents of the update and home partition you can do this right now. Otherwise backup whatever is there you want to keep, or proceed to Manual conversion and make sure you understand the process.

Otherwise, building as always with make image or bitbake -k edison-image will now produce edison-image-edison.btrfs as well.

This needs some pre-processing before it can be used. If you use make image that will be done automatically.

If you build your image using bitbake -k edison-image, you can use make postbuild or alternatively:


will rearrange so that the image contains @, @modules and @home subvolumes.

It can then be flashed using:

./flashall --btrfs

This will resize the boot partition and discard the update and home partition. /home will be mounted with a subvolume called @home. The root’s home directory will be on /root to prevent boot problems when there is a problem mounting @home.

Flashing will take quite a bit longer than you are used to, due to the (Yocto’s default) size of the image. Even though all that space is not used.

The good news is, this is probably the last time you will be using flashall.sh (unless you horribly break something and want to start over).

After you have the btrfs based image running you can use btrfsFlashOta.sh. This sends a btrfs snapshot (subvolume) to Edison that you can boot separately.

Further btrfsFlashOta can send/update/delete a kernel, update U-Boot and U-Boot Env. Basically this implements the functionality of flashall.sh without relying on a USB connection.

Manual conversion

This is what we want to accomplish:

  1. Increase the size of boot
  2. Install rescue image into boot
  3. Add the rescue image to U-Boot boot variables
  4. Boot into rescue image
  5. Delete the update partition
  6. Resize rootfs to use available space
  7. Install btrfs image into rootfs
  8. Convert home ext4 partition to btrfs and take snapshot @home
  9. Btrfs send @home snapshot to rootfs pool
  10. Delete the home partition
  11. Resize rootfs to use all available space
  12. Rename rootfs to home
  13. Boot into home

The following is intended more to document what’s going on in the process then to really do the conversion this way. But if you really want to, you can.

1 - 3. Starting point: ext4 Kirkstone image with btrfs patches

If you already had this flashed you can skip directory to step 4.

Build and flashall (but see Warning below) as you would normally a version with the btrfs patches. This will:

  1. Update U-Boot to a btrfs enabled version
  2. Install in the boot partition: bzImage and initrd. The kernel has btrfs enabled and the initrd has ext4 and btrfs tools for repair and maintenance. Even though the partition is called boot (fat formatted) we will use it as a rescue image only. Currently the size does not exceed 20MiB and should easily fit, but we will take the opportunity to increase the size to 64 MiB to allow it to function as a usb disk when in gadget mode.
    Expanding boot will move the start of update partition and make it unreadable.
  3. Update the U-Boot environment to enable booting the rescue image.
    This is how your partitions will be redefined:

    Also there will be some new variables in U-Boot:

    boot_rescue=zboot ${loadaddr} 0x1800000 0x6000000 0x1800000
    bootargs_rescue=debugshell=0 tty1 console=ttyS2,115200n8 root=/dev/mmcblk0p7 rootfstype=vfat systemd.unit=multi-user.target hardware_id=00
    do_rescue=setenv bootargs ${bootargs_common} ${bootargs_rescue}; run load_rescue; run boot_rescue
    load_rescue=load mmc 0:7 ${loadaddr} bzImage;load mmc 0:7 0x6000000 initrd

If anything goes wrong the Rescue image will have the tools to fix it (in the worst case you can of course always do flashall --recovery and start over, but that is a bit tedious isn’t it).

To get to Rescue:

press <ESC> during boot to enter U-Boot

run do_rescue

4. Boot into ext4 Kirkstone image

Rebooting Edison should take you into Kirkstone on mmcblk0p8 (rootfs).

The first time it will run the /sbin/post-install.sh script, let it complete. It may be that the update partition has been fat32 formatted earlier, or maybe it’s corrupt. If it’s fat formatted and you are connected over usb this partition maybe mounted on your host (as a gadget), you might want to unmount it now.

Anyhow we are going to delete it in the next step.

5 - 6. Rearrange partitions

parted /dev/mmcblk0

unit s # show size in sectors
print  # check if all partitions are as in table above

    Model: MMC H4G1d (sd/mmc)
    Disk /dev/mmcblk0: 7634944s
    Sector size (logical/physical): 512B/512B
    Partition Table: gpt
    Disk Flags: 
    Number  Start     End       Size      File system  Name         Flags
     1      2048s     6143s     4096s                  u-boot0      msftdata
     2      6144s     8191s     2048s                  u-boot-env0  msftdata
     3      8192s     12287s    4096s                  u-boot1      msftdata
     4      12288s    14335s    2048s                  u-boot-env1  msftdata
     5      14336s    16383s    2048s     ext2         factory      msftdata
     6      16384s    65535s    49152s                 panic        msftdata
     7      65536s    196607s   131072s   fat16        boot         msftdata
     8      196608s   3342335s  3145728s  ext4         rootfs       msftdata
     9      3342336s  4849663s  1507328s  fat32        update       msftdata
    10      4849664s  7634910s  2785247s  ext4         home         msftdata

rm 9   # delete update partition !! can not be recovered

resizepart 8 # until 1 sector before start of home (partition 10)
    Warning: Partition /dev/mmcblk0p8 is being used. Are you sure you want to continue?
    Yes/No? yes                                                               
    End?  [3342335s]? 4849663s                                               


Now resize the filesystem rootfs to make use of the larger partition:

/lib/systemd/systemd-growfs /

Now you have 1 large rootfs and 1 home partition.

root@edison:~# df
Filesystem      1K-blocks   Used Available Use% Mounted on
none               465160      4    465156   1% /dev
/dev/mmcblk0p8    2146112 863324   1162868  43% /
tmpfs              479208      0    479208   0% /dev/shm
tmpfs              479208    748    478460   1% /run
tmpfs              479208      0    479208   0% /sys/fs/cgroup
tmpfs              479208      4    479204   1% /tmp
/dev/mmcblk0p5       1003     21       911   3% /factory
tmpfs               95840      0     95840   0% /run/user/0
/dev/mmcblk0p10   1337936   5048   1316504   1% /home

7. Install btrfs image

It is possible to convert the existing ext4 partition to btrfs. But it is much less work to just flash the already built btrfs image. Building with make image or bitbake -k edison-image produced a edison-image-edison.btrfs in addition to edison-image-edison.ext4. This needs some pre-processing before it can be used:

make postbuild

will rearrange so that the image contains @, @modules and @home subvolumes.

The following steps require accessing the Edison using DFU. If you have not followed the instructions in Avoiding Permissions Issues, you will need to invoke dfu-util as root with sudo each time.

To flash the Edison Arduino board you need 2 USB connections.

  1. Connect the first USB cable to the USB port marked as 3 in the photograph below.
    This cable will be your serial connection to the Edison. To connect to the edison you might use a terminal emulator like gtkterm. The serial port is probably /dev/ttyUSB0 and the baud rate is 115200 with parity none. If you prefer the command line you can use screen /dev/ttyUSB0 115200.

  2. The second cable to attach goes to the USB port marked as 2 in the photograph below.
    This port is a special port that can act as USB host or USB slave of which only one is active at a time. As you will be connecting to a host port of your PC, it needs to be configured as slave on the Edison. Push the switch down in the direction of the micro USB ports so that the port is enabled. Alt tekst

  3. On Ubuntu you might need to install the package dfu-util.

  4. Press the reset button (under the text RESET in the picture above).

  5. In your terminal press the ESC key to interrupt the boot process.

  6. You will probably see:

    U-Boot 2020.04
  7. In your terminal type at the boot> prompt:

    run do_force_flash_os
  8. In a second terminal window:

    dfu-util -v -d 8087:0a99 --alt rootfs -D edison-image-edison.btrfs

    This will flash the image to the rootfs partition. In the first terminal window you may watch the flashing to complete.

    DFU complete CRC32: 0xf340088e  
    DOWNLOAD ... OK  

    Now flash the btrfs enabled U-Boot environment and it’s backup and reboot

    dfu-util -v -d 8087:0a99 --alt u-boot-env0 -D edison-btrfs.bin
    dfu-util -v -d 8087:0a99 --alt u-boot-env1 -D edison-btrfs.bin -R

8 - 12. Move home to rootfs/@home

First we convert home to btrfs, then take a snapshot and send it to rootfs:

mkdir /media/home
btrfs-convert /dev/mmncblk0p10
btrfs scan
mount btrfs -t btrfs /dev/mmncblk0p10 /media/home
btrfs subvolume snapshot -r /media/home /media/home/@home
btrfs send /media/home/@home | btrfs receive /media/rootfs
btrfs property set -ts /media/rootfs/@home ro false
btrfs balance start /media/rootfs # you could skip this, but if you run it let it complete
umount /media/home
umount /media/rootfs

Get rid of the home partition:

parted /dev/mmcblk0

unit s # show size in sectors
rm 10  # delete home partition !! can not be recovered
resizepart 8 7634910

Rename the rootfs partition to home

name 8 home

Mount and resize home:

mount btrfs -t btrfs /dev/mmncblk0p8 /media/rootfs
btrfs filesystem resize max /media/rootfs

13. Boot into home

umount /media/rootfs

Resetting the Edison should boot you right into the kernel and initrd located in the @boot subvolume on the home partition. The root subvolume @, will be mounted on / and @boot on /boot after the switchroot.