List all btrfs filesystems and subvolumes in shell

Question

Is there a convenient way to get information on all btrfs filesystems subvolumes without resorting to C, i.e. in POSIX shell ?

/sys/fs/btrfs contains info only on filesystems, nothing on subvolumes, so currently i end up mounting all filesystems in a temp folder, scanning them with btrfs subvol list, then parsing the resulting output. Needless to say, that is fairly ugly.

This is with a 3.16.x kernel and btrfs-progs v3.14.1 (from stock Ubuntu 14.10).

Below is the (ugly) script I'm currently using. I know I could get the info I need using pure C, and that's probably what I'll end up doing, but I was wondering if there was a simpler, more elegant way.

#!/bin/bash

for i in /sys/fs/btrfs/*[!features]; do 

  device="/dev/$(basename $i/devices/*)"
  mountpoint=/var/lib/btrfs/tmp/mnt/$(basename "$i")

  [ -d "$mountpoint" ] || mkdir "$mountpoint"

  grep -qs $mountpoint /proc/mounts
  [ $? -ne 0 ] && mount -v "$device" "$mountpoint"

  while read -r subvol; do
    # whatever you want
  done < <(btrfs subvolume list "$mountpoint")

  umount $mountpoint
  rmdir $mountpoint
done

Answer 1

/sys/fs/btrfs does't list all btrfs filesystem (e.g not mounted one), tested on Debian / Ubuntu (4.14.0-1 / 4.10.0-42).
I would use btrfs progs to search them:

btrfs filesystem show | awk '/ path /{print $NF}'

And since btrfs progs can list subvolumes only of mounted fs, your script is not far from what I would use:

#!/bin/bash

readarray -t btdev < <(sudo btrfs filesystem show | awk '/ path /{print $NF}' )

for i in "${btdev[@]}"; do 

  device="${i}"
  mountpoint=/var/lib/btrfs/tmp/mnt/$(basename "$i")

  [ -d "$mountpoint" ] || mkdir "$mountpoint"

  grep -qs $mountpoint /proc/mounts
  [ $? -ne 0 ] && mount -v "$device" "$mountpoint"

  while read -r subvol; do
    # whatever you want
  done < <(btrfs subvolume list "$mountpoint")

  umount $mountpoint
  rmdir $mountpoint
done

Not tested against multi-device filesystem (raid-0/1/10/5/6)