Be more helpful when requested compression is not available

gen_initramfs.sh

@@ -705,9 +705,15 @@ create_initramfs() {
 			cmd_bzip2=$(type -p bzip2)
 			cmd_gzip=$(type -p gzip)
 			cmd_lzop=$(type -p lzop)
+			pkg_xz='app-arch/xz-utils'
+			pkg_lzma='app-arch/xz-utils'
+			pkg_bzip2='app-arch/bzip2'
+			pkg_gzip='app-arch/gzip'
+			pkg_lzop='app-arch/lzop'
 			local compression
 			case ${COMPRESS_INITRD_TYPE} in
-				xz|lzma|bzip2|gzip|lzo) compression=${COMPRESS_INITRD_TYPE} ;;
+				xz|lzma|bzip2|gzip) compression=${COMPRESS_INITRD_TYPE} ;;
+				lzo) compression=lzop ;;
 				best)
 					if grep -sq '^CONFIG_RD_XZ=y' ${KERNEL_DIR}/.config && test -n "${cmd_xz}" ; then
 						compression=xz
@@ -718,18 +724,24 @@ create_initramfs() {
 					elif grep -sq '^CONFIG_RD_GZIP=y' ${KERNEL_DIR}/.config && test -n "${cmd_gzip}" ; then
 						compression=gzip
 					elif grep -sq '^CONFIG_RD_LZO=y' ${KERNEL_DIR}/.config && test -n "${cmd_lzop}" ; then
-						compression=lzo
+						compression=lzop
 					fi ;;
 				*)
 					gen_die "Compression '${COMPRESS_INITRD_TYPE}' unknown"
 					;;
 			esac
+
+			# Check for actual availability
+			cmd_variable_name=cmd_${compression}
+			pkg_variable_name=pkg_${compression}
+			[[ -z "${!cmd_variable_name}" ]] && gen_die "Compression '${compression}' is not available. Please install package '${!pkg_variable_name}'."
+
 			case $compression in
 				xz) compress_ext='.xz' compress_cmd="${cmd_xz} -e --check=none -z -f -9" ;;
 				lzma) compress_ext='.lzma' compress_cmd="${cmd_lzma} -z -f -9" ;;
 				bzip2) compress_ext='.bz2' compress_cmd="${cmd_bzip2} -z -f -9" ;;
 				gzip) compress_ext='.gz' compress_cmd="${cmd_gzip} -f -9" ;;
-				lzo) compress_ext='.lzo' compress_cmd="${cmd_lzop} -f -9" ;;
+				lzop) compress_ext='.lzo' compress_cmd="${cmd_lzop} -f -9" ;;
 			esac
 	
 			if [ -n "${compression}" ]; then