gen_initramfs: embed btrfs-progs utils in initramfs

This patch comes from Dennis 'dlan' Lan through bug #481116.

gen_determineargs.sh

@@ -125,6 +125,7 @@ determine_real_args() {
 	set_config_with_override STRING MDADM_CONFIG         CMD_MDADM_CONFIG
 	set_config_with_override BOOL   E2FSPROGS            CMD_E2FSPROGS            "no"
 	set_config_with_override BOOL   ZFS                  CMD_ZFS
+	set_config_with_override BOOL   BTRFS                CMD_BTRFS
 	set_config_with_override BOOL   VIRTIO               CMD_VIRTIO				  "no"
 	set_config_with_override BOOL   MULTIPATH            CMD_MULTIPATH
 	set_config_with_override BOOL   FIRMWARE             CMD_FIRMWARE

gen_initramfs.sh

@@ -367,6 +367,23 @@ append_zfs(){
 	rm -rf "${TEMP}/initramfs-zfs-temp" > /dev/null
 }
 
+append_btrfs() {
+	if [ -d "${TEMP}/initramfs-btrfs-temp" ]
+	then
+		rm -r "${TEMP}/initramfs-btrfs-temp"
+	fi
+
+	# Copy binaries
+	copy_binaries "${TEMP}/initramfs-btrfs-temp" /sbin/{btrfs,btrfsck,mkfs.btrfs}
+
+	cd "${TEMP}/initramfs-btrfs-temp/"
+	log_future_cpio_content
+	find . -print | cpio ${CPIO_ARGS} --append -F "${CPIO}" \
+			|| gen_die "compressing btrfs cpio"
+	cd "${TEMP}"
+	rm -rf "${TEMP}/initramfs-btrfs-temp" > /dev/null
+}
+
 append_splash(){
 	splash_geninitramfs=`which splash_geninitramfs 2>/dev/null`
 	if [ -x "${splash_geninitramfs}" ]
@@ -922,6 +939,8 @@ create_initramfs() {
 
 	append_data 'zfs' "${ZFS}"
 
+	append_data 'btrfs' "${BTRFS}"
+
 	append_data 'blkid' "${DISKLABEL}"
 
 	append_data 'splash' "${SPLASH}"