BTRFS on an encrypted resizable loop device

Goal: have an encrypted loop device containing a btrfs filesystem. Be able to extend this filesystem.

Setup

Create a file to be used as the encrypted container 

dd if=/dev/zero of=/data/dsk1 bs=1M count=500

Assign a loop device 

losetup /dev/loop1 /data/dsk1

Crypt the device : 

cryptsetup -c aes --verify-passphrase create dsk1 /dev/loop1

Format filesystem encrypted in the loop device 

mkfs.btrfs /dev/mapper/dsk1

Now we can mount it 

mount -t btrfs /dev/mapper/dsk1 /mnt/tmp

Unmount and detach

umount /mnt/tmp
cryptsetup remove dsk1
losetup -d /dev/loop1

Reattach and mount

losetup /dev/loop1 /data/dsk1
cryptsetup create dsk1 /dev/loop1
mount /dev/mapper/dsk1 /mnt/tmp

Resize the container

Get size : 

df -h|grep dsk1
/dev/mapper/dsk1      500M   56K  408M   1% /mnt/tmp

Make the file bigger 

dd if=/dev/zero of=/data/dsk1 bs=1M count=300 conv=notrunc oflag=append

Resize the btrfs file system 

btrfs filesystem resize max /mnt/tmp

Here we are : 

df -h|grep dsk1
/dev/mapper/dsk1      800M   56K  708M   1% /mnt/tmp

Encrypted filesystem resized mounted.