mkinitramfs: Support -h and --help options

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

mkinitramfs

@@ -13,7 +13,7 @@ export BUSYBOXDIR
 
 usage()
 {
-	cat >&2 << EOF
+	cat << EOF
 
 Usage: ${0} [OPTION]... -o outfile [version]
 
@@ -26,10 +26,15 @@ Options:
 
 See mkinitramfs(8) for further details.
 EOF
+}
+
+usage_error()
+{
+	usage >&2
 	exit 2
 }
 
-OPTIONS=$(getopt -o c:d:ko:r:v -n "$0" -- "$@")
+OPTIONS=$(getopt -o c:d:hko:r:v --long help -n "$0" -- "$@")
 
 # Check for non-GNU getopt
 # shellcheck disable=SC2181
@@ -51,6 +56,10 @@ while true; do
 			exit 1
 		fi
 		;;
+	-h|--help)
+		usage
+		exit 0
+		;;
 	-o)
 		outfile="$2"
 		shift 2
@@ -128,7 +137,7 @@ if [ -n "${UMASK:-}" ]; then
 fi
 
 if [ -z "${outfile}" ]; then
-	usage
+	usage_error
 fi
 
 touch "$outfile"

mkinitramfs.8

@@ -16,6 +16,8 @@ mkinitramfs \- low-level tool for generating an initramfs image
 .IR root ]
 .RB [ \-v ]
 .RI [ version ]
+.br
+.BR mkinitramfs " " -h
 
 .SH DESCRIPTION
 The
@@ -49,7 +51,6 @@ setting in
 \fB\-d \fI confdir
 Set an alternate configuration directory.
 
-.TP
 .TP
 \fB\-k
 Keep the temporary directory used to make the image.
@@ -75,6 +76,10 @@ Set the verbose mode output.
 Set the kernel version of the initramfs image
 (defaults to the running kernel).
 
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+Display usage information and exit.
+
 .SH ENVIRONMENT
 .B mkinitramfs
 honours the