Create BTRFS subvolumes by default

[danboid]

Under Ubuntu when you install using BTRFS and Debian when you install to BTRFS using the Calamares live GUI installer, both installers create a subvolume called @home for the /home directory and another subvol called @ for the rest of the filesystem. This layout enables users to use timeshift to easily (and automatically with timeshift-autosnap-apt) create BTRFS snapshots and restore them using the command line or the timeshift GUI and restore their OS whilst optionally keeping users files stored under /home intact.

 

I would like to see the armbian installation script configure BTRFS in this same manner.

Edited April 26, 2023 by danboid

[c0rnelius]

This is a pretty easy add. Basically after creating the btrfs filesystem, mount the LOOP and create the subvolume, now unmount the LOOP and remount it with the correct flags.

 

Lets pretend these are the variables.

P_ROOTFS="/mnt/p1"

IMAGE_LOOP_DEV_ROOTFS="/dev/loop1p1"

 

mkfs.btrfs -f -L ROOTFS ${IMAGE_LOOP_DEV_ROOTFS}
mount "${IMAGE_LOOP_DEV_ROOTFS}" ${P_ROOTFS}
btrfs subvolume create ${P_ROOTFS}/@
umount ${P_ROOTFS}
mount -o compress=lzo,noatime,subvol=@ ${IMAGE_LOOP_DEV_ROOTFS} ${P_ROOTFS}

 

Where all this would reside in the Armbian framework, I'm not really sure? But in general it wouldn't take that much effort to introduce. One issue I can see popping up, is that U-Boot "last I checked?" doesn't support BTRFS subvolumes. So if subvolumes were an option, the image would require a VFAT or EXT4 BOOT partition.

 

[danboid]

Thanks for that c0rnelius!

 

I was unaware that u-boot (probably still) doesn't support BTRFS subvols. Hopefully they can add that so we'd be able to avoid the extra boot partition.

 

I will look into that today.

EDIT

It looks like it does have subvol support :

https://github.com/u-boot/u-boot/blob/master/fs/btrfs/subvolume.c

Edited April 26, 2023 by danboid

[c0rnelius]

I've seen that in there too, but I've never been able to get a subvolume to boot without using a boot partition. There is also CONFIG_CMD_BTRFS and I could be completely off here, but my thought was maybe a command needs to be executed with a boot script in order for the subvolume to be read/found? I normally use extlinux and with CONFIG_FS_BTRFS & CONFIG_CMD_BTRFS enabled it has always been a no go for me. Maybe someone else here has a thought on the subject?

 

EDIT

 

I tried 3 times getting this working using a Radxa Zero and it was a no-go for a single partition. Once I added a boot partition, it booted right up.

 

radxazero: ~  $ lsblk
NAME         MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
mmcblk0      179:0    0 29.7G  0 disk 
├─mmcblk0p1  179:1    0  253M  0 part /boot
└─mmcblk0p2  179:2    0 29.5G  0 part /
mmcblk1      179:32   0 14.6G  0 disk 
├─mmcblk1p1  179:33   0  253M  0 part 
└─mmcblk1p2  179:34   0 14.3G  0 part 
mmcblk1boot0 179:64   0    4M  1 disk 
mmcblk1boot1 179:96   0    4M  1 disk 
zram0        253:0    0    1G  0 disk [SWAP]
radxazero: ~  $ findmnt /boot; findmnt /
TARGET SOURCE         FSTYPE OPTIONS
/boot  /dev/mmcblk0p1 ext4   rw,relatime
TARGET SOURCE             FSTYPE OPTIONS
/      /dev/mmcblk0p2[/@] btrfs  rw,noatime,compress=lzo,ssd,space_cache=v2,subvol

 

Edited April 26, 2023 by c0rnelius