Show the difference between two btrfs subvolumes/snapshots

btrfs-subvolume-diff.sh

#!/bin/bash
#
# Author: http://serverfault.com/users/96883/artfulrobot
#
# This script will show most files that got modified or added.
# Renames and deletions will not be shown.
# Read limitations on:
# http://serverfault.com/questions/399894/does-btrfs-have-an-efficient-way-to-compare-snapshots
#
# btrfs send is the best way to do this long term, but as of kernel
# 3.14, btrfs send cannot just send a list of changed files without
# scanning and sending all the changed data blocks along.

usage() { echo $@ >&2; echo "Usage: $0 <older-snapshot> <newer-snapshot>" >&2; exit 1; }

[ $# -eq 2 ] || usage "Incorrect invocation";
SNAPSHOT_OLD=$1;
SNAPSHOT_NEW=$2;

[ -d $SNAPSHOT_OLD ] || usage "$SNAPSHOT_OLD does not exist";
[ -d $SNAPSHOT_NEW ] || usage "$SNAPSHOT_NEW does not exist";

OLD_TRANSID=`btrfs subvolume find-new "$SNAPSHOT_OLD" 9999999`
OLD_TRANSID=${OLD_TRANSID#transid marker was }
[ -n "$OLD_TRANSID" -a "$OLD_TRANSID" -gt 0 ] || usage "Failed to find generation for $SNAPSHOT_NEW"

btrfs subvolume find-new "$SNAPSHOT_NEW" $OLD_TRANSID | sed '$d' | cut -f17- -d' ' | sort | uniq

This is another solution:

btrfs send --no-data  -p SHAPSHOT_OLD  SHAPSHOT_NEW  |  btrfs receive --dump  |  grep ^update_extent