secvarctl: display enabled backends in --help, allow empty -m to quer…

…y enabled backends

Currently, there is no way to know which backends are enabled in a given
binary. Therefore, add the enabled backends to the --help output, as
well as display the enabled backends if -m is called without any
following argument.

This also fixes a bug where argv was checked for NULL instead of *argv,
which could have led to a segmentation fault.

Signed-off-by: Eric Richter <[email protected]>

secvarctl.c

@@ -61,6 +61,14 @@ void version()
 	printf("secvarctl v%s\n", secvarctl_version);
 }
 
+void enabled_backends()
+{
+	printf("Enabled backends:\n");
+	for (enum backends back = 0; back < BACKEND_UNKNOWN; back++) {
+		printf(" - %s\n", backends[back].format);
+	}
+}
+
 void usage()
 {
 	version();
@@ -86,7 +94,8 @@ void usage()
 	       "management,\n\t\t\t"
 	       "use 'secvarctl [MODE] generate --usage/help' for more information\n"
 #endif
-	);
+	       "\n");
+	enabled_backends();
 }
 
 void help()
@@ -195,9 +204,9 @@ int main(int argc, char *argv[])
 		} else if (!strcmp("-m", *argv) || !strcmp("--mode", *argv)) {
 			argv++;
 			argc--;
-			if (argv == NULL) {
-				prlog(PR_WARNING, "No mode name supplied\n");
-				return UNKNOWN_COMMAND;
+			if (*argv == NULL) {
+				enabled_backends();
+				return SUCCESS;
 			}
 			for (i = 0; i < sizeof(backend_names) / sizeof(backend_names[0]); i++) {
 				if (!strcmp(*argv, backend_names[i].name)) {