1 files changed, 236 insertions, 0 deletions
diff --git a/sysutils/lockf/files/lockf.c b/sysutils/lockf/files/lockf.c
new file mode 100644
index 00000000000..7b14014e3e5
--- /dev/null
+++ b/sysutils/lockf/files/lockf.c
@@ -0,0 +1,236 @@
+/*
+ * Copyright (C) 1997 John D. Polstra.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY JOHN D. POLSTRA AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL JOHN D. POLSTRA OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+
+#include <sys/types.h>
+#include <sys/wait.h>
+
+#include <err.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sysexits.h>
+#include <unistd.h>
+
+static int acquire_lock(const char *name, int flags);
+static void cleanup(void);
+static void killed(int sig);
+static void timeout(int sig);
+static void usage(void);
+static void wait_for_lock(const char *name);
+
+static const char *lockname;
+static int lockfd = -1;
+static int keep;
+static volatile sig_atomic_t timed_out;
+
+/*
+ * Execute an arbitrary command while holding a file lock.
+ */
+int
+main(int argc, char **argv)
+{
+	int ch, silent, status, waitsec;
+	pid_t child;
+
+	silent = keep = 0;
+	waitsec = -1;	/* Infinite. */
+	while ((ch = getopt(argc, argv, "skt:")) != -1) {
+		switch (ch) {
+		case 'k':
+			keep = 1;
+			break;
+		case 's':
+			silent = 1;
+			break;
+		case 't':
+		{
+			char *endptr;
+			waitsec = strtol(optarg, &endptr, 0);
+			if (*optarg == '\0' || *endptr != '\0' || waitsec < 0)
+				errx(EX_USAGE,
+				    "invalid timeout \"%s\"", optarg);
+		}
+			break;
+		default:
+			usage();
+		}
+	}
+	if (argc - optind < 2)
+		usage();
+	lockname = argv[optind++];
+	argc -= optind;
+	argv += optind;
+	if (waitsec > 0) {		/* Set up a timeout. */
+		struct sigaction act;
+
+		act.sa_handler = timeout;
+		sigemptyset(&act.sa_mask);
+		act.sa_flags = 0;	/* Note that we do not set SA_RESTART. */
+		sigaction(SIGALRM, &act, NULL);
+		alarm(waitsec);
+	}
+	/*
+	 * If the "-k" option is not given, then we must not block when
+	 * acquiring the lock.  If we did, then the lock holder would
+	 * unlink the file upon releasing the lock, and we would acquire
+	 * a lock on a file with no directory entry.  Then another
+	 * process could come along and acquire the same lock.  To avoid
+	 * this problem, we separate out the actions of waiting for the
+	 * lock to be available and of actually acquiring the lock.
+	 *
+	 * That approach produces behavior that is technically correct;
+	 * however, it causes some performance & ordering problems for
+	 * locks that have a lot of contention.  First, it is unfair in
+	 * the sense that a released lock isn't necessarily granted to
+	 * the process that has been waiting the longest.  A waiter may
+	 * be starved out indefinitely.  Second, it creates a thundering
+	 * herd situation each time the lock is released.
+	 *
+	 * When the "-k" option is used, the unlink race no longer
+	 * exists.  In that case we can block while acquiring the lock,
+	 * avoiding the separate step of waiting for the lock.  This
+	 * yields fairness and improved performance.
+	 */
+	lockfd = acquire_lock(lockname, O_NONBLOCK);
+	while (lockfd == -1 && !timed_out && waitsec != 0) {
+		if (keep)
+			lockfd = acquire_lock(lockname, 0);
+		else {
+			wait_for_lock(lockname);
+			lockfd = acquire_lock(lockname, O_NONBLOCK);
+		}
+	}
+	if (waitsec > 0)
+		alarm(0);
+	if (lockfd == -1) {		/* We failed to acquire the lock. */
+		if (silent)
+			exit(EX_TEMPFAIL);
+		errx(EX_TEMPFAIL, "%s: already locked", lockname);
+	}
+	/* At this point, we own the lock. */
+	if (atexit(cleanup) == -1)
+		err(EX_OSERR, "atexit failed");
+	if ((child = fork()) == -1)
+		err(EX_OSERR, "cannot fork");
+	if (child == 0) {	/* The child process. */
+		close(lockfd);
+		execvp(argv[0], argv);
+		warn("%s", argv[0]);
+		_exit(1);
+	}
+	/* This is the parent process. */
+	signal(SIGINT, SIG_IGN);
+	signal(SIGQUIT, SIG_IGN);
+	signal(SIGTERM, killed);
+	if (waitpid(child, &status, 0) == -1)
+		err(EX_OSERR, "waitpid failed");
+	return (WIFEXITED(status) ? WEXITSTATUS(status) : EX_SOFTWARE);
+}
+
+/*
+ * Try to acquire a lock on the given file, creating the file if
+ * necessary.  The flags argument is O_NONBLOCK or 0, depending on
+ * whether we should wait for the lock.  Returns an open file descriptor
+ * on success, or -1 on failure.
+ */
+static int
+acquire_lock(const char *name, int flags)
+{
+	int fd;
+
+	if ((fd = open(name, O_RDONLY|O_CREAT|O_EXLOCK|flags, 0666)) == -1) {
+		if (errno == EAGAIN || errno == EINTR)
+			return (-1);
+		err(EX_CANTCREAT, "cannot open %s", name);
+	}
+	return (fd);
+}
+
+/*
+ * Remove the lock file.
+ */
+static void
+cleanup(void)
+{
+
+	if (keep)
+		flock(lockfd, LOCK_UN);
+	else
+		unlink(lockname);
+}
+
+/*
+ * Signal handler for SIGTERM.  Cleans up the lock file, then re-raises
+ * the signal.
+ */
+static void
+killed(int sig)
+{
+
+	cleanup();
+	signal(sig, SIG_DFL);
+	if (kill(getpid(), sig) == -1)
+		err(EX_OSERR, "kill failed");
+}
+
+/*
+ * Signal handler for SIGALRM.
+ */
+static void
+timeout(int sig __unused)
+{
+
+	timed_out = 1;
+}
+
+static void
+usage(void)
+{
+
+	fprintf(stderr,
+	    "usage: lockf [-ks] [-t seconds] file command [arguments]\n");
+	exit(EX_USAGE);
+}
+
+/*
+ * Wait until it might be possible to acquire a lock on the given file.
+ * If the file does not exist, return immediately without creating it.
+ */
+static void
+wait_for_lock(const char *name)
+{
+	int fd;
+
+	if ((fd = open(name, O_RDONLY|O_EXLOCK, 0666)) == -1) {
+		if (errno == ENOENT || errno == EINTR)
+			return;
+		err(EX_CANTCREAT, "cannot open %s", name);
+	}
+	close(fd);
+}