exporting capability code/name pairs (try 2nd)

index dc13c06..1b9ed45 100644
@@ -4,6 +4,7 @@
  * This sets the capabilities of a given file.
  */
 
+#include <dirent.h>
 #include <errno.h>
 #include <stdio.h>
 #include <string.h>

@@ -13,10 +14,34 @@
 
 static void usage(void)
 {
+    DIR *dirp;
+
     fprintf(stderr,
 	    "usage: setcap [-q] (-r|-|<caps>) <filename> "
 	    "[ ... (-r|-|<capsN>) <filenameN> ]\n"
 	);
+
+    dirp = opendir("/sys/kernel/capability");
+    if (dirp) {
+	struct dirent *dent;
+	int len, width = 99999;
+
+	fprintf(stderr,
+		"\nsupported capabilities:");
+	while ((dent = readdir(dirp)) != NULL) {
+	    if (!!strncmp("cap_", dent->d_name, 4))
+		continue;
+	    len = strlen(dent->d_name);
+	    if (width + len > 72) {
+		fprintf(stderr, "\n\t");
+		width = 8;
+	    }
+	    fprintf(stderr, "%s ", dent->d_name);
+	    width += len;
+	}
+	fputc('\n', stderr);
+	closedir(dirp);
+    }
     exit(1);
 }