--- /usr/share/initramfs-tools/hooks/cryptroot	2014-08-17 20:44:51.515290131 +0100
+++ ./debian/initramfs/cryptroot-hook	2014-08-17 21:36:14.359222493 +0100
@@ -16,8 +16,8 @@
 
 . /usr/share/initramfs-tools/hook-functions
 
-get_root_device() {
-	local device mount type options dump pass
+get_root_devices() {
+	local device devices mount type options dump pass canonical
 
 	if [ ! -r /etc/fstab ]; then
 		return 1
@@ -26,9 +26,21 @@
 	grep -s '^[^#]' /etc/fstab | \
 	while read device mount type options dump pass; do
 		if [ "$mount" = "/" ]; then
-			device=$(canonical_device "$device") || return 0
-			echo "$device"
-			return
+			if is_btrfs_filesystem "$device" ; then
+				devices=$(get_btrfs_siblings "$device")
+				if [ -z "$devices" ] ; then
+					echo "cryptsetup: BUG: internal failure to get btrfs siblings." >&2
+					devices="$device"
+				fi
+			else
+				devices="$device"
+			fi
+			for device in $devices ; do
+				if canonical=$(canonical_device "$device") ; then
+					echo $canonical
+				fi
+			done
+			return 0
 		fi
 	done
 }
@@ -168,6 +180,28 @@
 	return 0
 }
 
+is_btrfs_filesystem() {
+	blkid -t TYPE=btrfs $1 >/dev/null
+}
+
+is_btrfs_tool_available() {
+	which btrfs > /dev/null
+}
+
+get_btrfs_siblings() {
+	local node="$1"
+	if ! is_btrfs_tool_available ; then
+		echo "cryptsetup: WARNING: \"$node\" is btrfs, but btrfs tool is not available." >&2
+		echo "            If there are other devices in this filesystem they will not be" >&2
+		echo "            decrypted at boot time." >&2
+		echo "$node"
+		return 0
+	fi
+
+	btrfs filesystem show "$node" | grep /dev/ | \
+	   sed 's/[^\/]*\(\/dev\/[^ ]*\)/\1/g'
+}
+
 get_device_opts() {
 	local target source link extraopts rootopts opt
 	target="$1"
@@ -502,6 +536,9 @@
 setup="no"
 rootdev=""
 resumedevs=""
+# This set contains rootdev, but may contain more devices in case of filesystems
+# which are spanned accross several devices (e.g. btrfs).
+all_rootdevs=""
 
 # Include cryptsetup modules, regardless of _this_ machine
 # configuration
@@ -511,15 +548,17 @@
 
 # Find the root and resume device(s)
 if [ -r /etc/crypttab ]; then
-	rootdev=$(get_root_device)
-	if [ -z "$rootdev" ]; then
+	all_rootdevs=$(get_root_devices)
+	if [ -z "$all_rootdevs" ]; then
 		echo "cryptsetup: WARNING: could not determine root device from /etc/fstab" >&2
+	else
+		rootdev=$(echo $all_rootdevs | ( read first rest ; echo $first ))
 	fi
 	resumedevs=$(get_resume_devices)
 fi
 
 # Load the config opts and modules for each device
-for dev in $rootdev $resumedevs ; do
+for dev in $all_rootdevs $resumedevs; do
 	if ! modules=$(add_device "$dev"); then
 		echo "cryptsetup: FAILURE: could not determine configuration for $dev" >&2
 		continue