fdtdump: make usage a bit more friendly

This starts a new usage framework and then cuts fdtdump over to it.
Now we can do `fdtdump -h` and get something useful back.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

fdtdump.c

@@ -117,21 +117,36 @@ static void dump_blob(void *blob)
 	}
 }
 
+/* Usage related data. */
+static const char usage_synopsis[] = "fdtdump [options] <file>";
+static const char usage_short_opts[] = USAGE_COMMON_SHORT_OPTS;
+static struct option const usage_long_opts[] = {
+	USAGE_COMMON_LONG_OPTS
+};
+static const char * const usage_opts_help[] = {
+	USAGE_COMMON_OPTS_HELP
+};
 
 int main(int argc, char *argv[])
 {
+	int opt;
+	const char *file;
 	char *buf;
 
-	if (argc < 2) {
-		fprintf(stderr, "supply input filename\n");
-		return 5;
+	while ((opt = util_getopt_long()) != EOF) {
+		switch (opt) {
+		case_USAGE_COMMON_FLAGS
+		}
 	}
+	if (optind != argc - 1)
+		long_usage("missing input filename");
+	file = argv[optind];
 
-	buf = utilfdt_read(argv[1]);
-	if (buf)
-		dump_blob(buf);
-	else
-		return 10;
+	buf = utilfdt_read(file);
+	if (!buf)
+		die("could not read: %s\n", file);
+
+	dump_blob(buf);
 
 	return 0;
 }

util.c

@@ -392,3 +392,57 @@ void util_version(void)
 	printf("Version: %s\n", DTC_VERSION);
 	exit(0);
 }
+
+void util_long_usage(const char *errmsg, const char *synopsis,
+		     const char *short_opts, struct option const long_opts[],
+		     const char * const opts_help[])
+{
+	FILE *fp = errmsg ? stderr : stdout;
+	const char a_arg[] = "<arg>";
+	size_t a_arg_len = strlen(a_arg) + 1;
+	size_t i;
+	int optlen;
+
+	fprintf(fp,
+		"Usage: %s\n"
+		"\n"
+		"Options: -[%s]\n", synopsis, short_opts);
+
+	/* prescan the --long opt length to auto-align */
+	optlen = 0;
+	for (i = 0; long_opts[i].name; ++i) {
+		/* +1 is for space between --opt and help text */
+		int l = strlen(long_opts[i].name) + 1;
+		if (long_opts[i].has_arg == a_argument)
+			l += a_arg_len;
+		if (optlen < l)
+			optlen = l;
+	}
+
+	for (i = 0; long_opts[i].name; ++i) {
+		/* helps when adding new applets or options */
+		assert(opts_help[i] != NULL);
+
+		/* first output the short flag if it has one */
+		if (long_opts[i].val > '~')
+			fprintf(fp, "      ");
+		else
+			fprintf(fp, "  -%c, ", long_opts[i].val);
+
+		/* then the long flag */
+		if (long_opts[i].has_arg == no_argument)
+			fprintf(fp, "--%-*s", optlen, long_opts[i].name);
+		else
+			fprintf(fp, "--%s %s%*s", long_opts[i].name, a_arg,
+				(int)(optlen - strlen(long_opts[i].name) - a_arg_len), "");
+
+		/* finally the help text */
+		fprintf(fp, "%s\n", opts_help[i]);
+	}
+
+	if (errmsg) {
+		fprintf(fp, "\nError: %s\n", errmsg);
+		exit(EXIT_FAILURE);
+	} else
+		exit(EXIT_SUCCESS);
+}

util.h

@@ -2,6 +2,7 @@
 #define _UTIL_H
 
 #include <stdarg.h>
+#include <getopt.h>
 
 /*
  * Copyright 2011 The Chromium Authors, All Rights Reserved.
@@ -184,4 +185,64 @@ void utilfdt_print_data(const char *data, int len);
  */
 void util_version(void) __attribute__((noreturn));
 
+/**
+ * Show usage and exit
+ *
+ * This helps standardize the output of various utils.  You most likely want
+ * to use the long_usage() helper below rather than call this.
+ *
+ * @param errmsg	If non-NULL, an error message to display
+ * @param synopsis	The initial example usage text (and possible examples)
+ * @param short_opts	The string of short options
+ * @param long_opts	The structure of long options
+ * @param opts_help	An array of help strings (should align with long_opts)
+ */
+void util_long_usage(const char *errmsg, const char *synopsis,
+		     const char *short_opts, struct option const long_opts[],
+		     const char * const opts_help[]) __attribute__((noreturn));
+
+/**
+ * Show usage and exit
+ *
+ * If you name all your usage variables with usage_xxx, then you can call this
+ * help macro rather than expanding all arguments yourself.
+ *
+ * @param errmsg	If non-NULL, an error message to display
+ */
+#define long_usage(errmsg) \
+	util_long_usage(errmsg, usage_synopsis, usage_short_opts, \
+			usage_long_opts, usage_opts_help)
+
+/**
+ * Call getopt_long() with standard options
+ *
+ * Since all util code runs getopt in the same way, provide a helper.
+ */
+#define util_getopt_long() getopt_long(argc, argv, usage_short_opts, \
+				       usage_long_opts, NULL)
+
+/* Helper for aligning long_opts array */
+#define a_argument required_argument
+
+/* Helper for usage_short_opts string constant */
+#define USAGE_COMMON_SHORT_OPTS "hV"
+
+/* Helper for usage_long_opts option array */
+#define USAGE_COMMON_LONG_OPTS \
+	{"help",      no_argument, NULL, 'h'}, \
+	{"version",   no_argument, NULL, 'V'}, \
+	{NULL,        no_argument, NULL, 0x0}
+
+/* Helper for usage_opts_help array */
+#define USAGE_COMMON_OPTS_HELP \
+	"Print this help and exit", \
+	"Print version and exit", \
+	NULL
+
+/* Helper for getopt case statements */
+#define case_USAGE_COMMON_FLAGS \
+	case 'h': long_usage(NULL); \
+	case 'V': util_version(); \
+	case '?': long_usage("unknown option");
+
 #endif /* _UTIL_H */