pidof: size optimizations (-50 bytes)

include/usage.h

@@ -2544,7 +2544,7 @@
 	USE_FEATURE_PIDOF_SINGLE( \
        "\n	-s	Display only a single PID") \
 	USE_FEATURE_PIDOF_OMIT( \
-       "\n	-o	Omit given pid") \
+       "\n	-o PID	Omit given pid") \
 	USE_FEATURE_PIDOF_OMIT( \
        "\n		Use %PPID to omit the parent pid of pidof itself")
 #define pidof_example_usage \

libbb/find_pid_by_name.c

@@ -9,6 +9,35 @@
 
 #include "libbb.h"
 
+/*
+In Linux we have three ways to determine "process name":
+1. /proc/PID/stat has "...(name)...", among other things. It's so-called "comm" field.
+2. /proc/PID/cmdline's first NUL-terminated string. It's argv[0] from exec syscall.
+3. /proc/PID/exe symlink. Points to the running executable file.
+
+kernel threads:
+ comm: thread name
+ cmdline: empty
+ exe: <readlink fails>
+
+executable
+ comm: first 15 chars of base name
+ (if executable is a symlink, then first 15 chars of symlink name are used)
+ cmdline: argv[0] from exec syscall
+ exe: points to executable (resolves symlink, unlike comm)
+
+script (an executable with #!/path/to/interpreter):
+ comm: first 15 chars of script's base name (symlinks are not resolved)
+ cmdline: /path/to/interpreter (symlinks are not resolved)
+ (script name is in argv[1], args are pushed into argv[2] etc)
+ exe: points to interpreter's executable (symlinks are resolved)
+
+If FEATURE_PREFER_APPLETS=y (and more so if FEATURE_SH_STANDALONE=y),
+some commands started from busybox shell, xargs or find are started by
+execXXX("/proc/self/exe", applet_name, params....)
+and therefore comm field contains "exe".
+*/
+
 /* find_pid_by_name()
  *
  *  Modified by Vladimir Oleynik for use with libbb/procps.c

procps/pidof.c

@@ -20,9 +20,9 @@ int pidof_main(int argc, char **argv);
 int pidof_main(int argc, char **argv)
 {
 	unsigned first = 1;
-	unsigned fail = 1;
 	unsigned opt;
 #if ENABLE_FEATURE_PIDOF_OMIT
+	char ppid_str[sizeof(int)*3 + 1];
 	llist_t *omits = NULL; /* list of pids to omit */
 	opt_complementary = "o::";
 #endif
@@ -35,14 +35,12 @@ int pidof_main(int argc, char **argv)
 #if ENABLE_FEATURE_PIDOF_OMIT
 	/* fill omit list.  */
 	{
-		char getppid_str[sizeof(int)*3 + 1];
+		llist_t *omits_p = omits;
-		llist_t * omits_p = omits;
 		while (omits_p) {
 			/* are we asked to exclude the parent's process ID?  */
-			if (!strncmp(omits_p->data, "%PPID", 5)) {
+			if (strcmp(omits_p->data, "%PPID") == 0) {
-				llist_pop(&omits_p);
+				sprintf(ppid_str, "%u", (unsigned)getppid());
-				snprintf(getppid_str, sizeof(getppid_str), "%u", (unsigned)getppid());
+				omits_p->data = ppid_str;
-				llist_add_to(&omits_p, getppid_str);
 			}
 			omits_p = omits_p->link;
 		}
@@ -56,27 +54,24 @@ int pidof_main(int argc, char **argv)
 		/* reverse the pidlist like GNU pidof does.  */
 		pidList = pidlist_reverse(find_pid_by_name(argv[optind]));
 		for (pl = pidList; *pl; pl++) {
-			SKIP_FEATURE_PIDOF_OMIT(const) unsigned omitted = 0;
 #if ENABLE_FEATURE_PIDOF_OMIT
 			if (opt & OPT_OMIT) {
 				llist_t *omits_p = omits;
 				while (omits_p) {
 					if (xatoul(omits_p->data) == *pl) {
-						omitted = 1;
+						goto omitting;
-						break;
+					}
-					} else
+					omits_p = omits_p->link;
-						omits_p = omits_p->link;
 				}
 			}
 #endif
-			if (!omitted) {
+			printf(" %u" + first, (unsigned)*pl);
-				printf(" %u" + first, (unsigned)*pl);
+			first = 0;
-				first = 0;
-			}
-			fail = (!ENABLE_FEATURE_PIDOF_OMIT && omitted);
-
 			if (ENABLE_FEATURE_PIDOF_SINGLE && (opt & OPT_SINGLE))
 				break;
+#if ENABLE_FEATURE_PIDOF_OMIT
+ omitting: ;
+#endif
 		}
 		free(pidList);
 		optind++;
@@ -87,5 +82,5 @@ int pidof_main(int argc, char **argv)
 	if (ENABLE_FEATURE_CLEAN_UP)
 		llist_free(omits, NULL);
 #endif
-	return fail ? EXIT_FAILURE : EXIT_SUCCESS;
+	return first; /* 1 (failure) - no processes found */
 }