Add primitive pidof(8)

Makefile

@@ -11,6 +11,7 @@ LIB = \
 	util/estrtol.o      \
 	util/grabmntinfo.o  \
 	util/proc.o         \
+	util/putword.o      \
 	util/recurse.o      \
 	util/tty.o
 
@@ -27,6 +28,7 @@ SRC = \
 	mkswap.c            \
 	mount.c             \
 	mountpoint.c        \
+	pidof.c             \
 	pivot_root.c        \
 	ps.c                \
 	reboot.c            \

pidof.c

@@ -0,0 +1,64 @@
+/* See LICENSE file for copyright and license details. */
+#include <sys/types.h>
+#include <dirent.h>
+#include <libgen.h>
+#include <stdio.h>
+#include <string.h>
+#include "proc.h"
+#include "util.h"
+
+static void
+usage(void)
+{
+	eprintf("usage: %s [program...]\n", argv0);
+}
+
+int
+main(int argc, char *argv[])
+{
+	DIR *dp;
+	struct dirent *entry;
+	pid_t pid;
+	struct procstat ps;
+	char cmdline[PATH_MAX], *cmd, *p;
+	int i, found = 0;
+
+	ARGBEGIN {
+	default:
+		usage();
+	} ARGEND;
+
+	if (!argc)
+		return 1;
+
+	if (!(dp = opendir("/proc")))
+		eprintf("opendir /proc:");
+
+	while ((entry = readdir(dp))) {
+		if (!pidfile(entry->d_name))
+			continue;
+		for (i = 0; i < argc; i++) {
+			pid = estrtol(entry->d_name, 10);
+			parsestat(pid, &ps);
+			if (parsecmdline(ps.pid, cmdline,
+					 sizeof(cmdline)) < 0) {
+				cmd = ps.comm;
+			} else {
+				if ((p = strchr(cmdline, ' ')))
+					*p = '\0';
+				cmd = basename(cmdline);
+			}
+			if (strcmp(cmd, argv[i]) == 0) {
+				putword(entry->d_name);
+				found++;
+			}
+		}
+	}
+
+	if (found)
+		putchar('\n');
+
+	closedir(dp);
+
+	return 0;
+}

util.h

@@ -12,5 +12,6 @@ void devtotty(int dev, int *tty_maj, int *tty_min);
 void enprintf(int, const char *, ...);
 void eprintf(const char *, ...);
 long estrtol(const char *, int);
+void putword(const char *);
 void recurse(const char *, void (*)(const char *));
 char *ttytostr(int tty_maj, int tty_min);

util/putword.c

@@ -0,0 +1,18 @@
+/* See LICENSE file for copyright and license details. */
+#include <stdbool.h>
+#include <stdio.h>
+
+#include "../util.h"
+
+void
+putword(const char *s)
+{
+	static bool first = true;
+
+	if(!first)
+		putchar(' ');
+
+	fputs(s, stdout);
+	first = false;
+}
+