FreeBSD lockf made to work on Linux

lockf_linux.diff

--- /usr/src/usr.bin/lockf/lockf.c	2019-05-04 13:19:22.297590000 -0400
+++ lockf_linux.c	2020-12-04 14:49:25.770507000 -0500
@@ -25,9 +25,6 @@
  * SUCH DAMAGE.
  */
 
-#include <sys/cdefs.h>
-__FBSDID("$FreeBSD: releng/12.0/usr.bin/lockf/lockf.c 326276 2017-11-27 15:37:16Z pfg $");
-
 #include <sys/types.h>
 #include <sys/wait.h>
 
@@ -171,11 +168,16 @@
 {
 	int fd;
 
-	if ((fd = open(name, O_RDONLY|O_EXLOCK|flags, 0666)) == -1) {
+	if ((fd = open(name, O_RDONLY|flags, 0666)) == -1) {
 		if (errno == EAGAIN || errno == EINTR)
 			return (-1);
 		err(EX_CANTCREAT, "cannot open %s", name);
 	}
+	if ((flock(fd, LOCK_EX | (flags & O_NONBLOCK ? LOCK_NB : 0))) == -1) {
+		if (errno == EAGAIN || errno == EINTR)
+			return (-1);
+		err(EX_CANTCREAT, "failed to acquire lock %s", name);
+	}
 	return (fd);
 }
 
@@ -210,7 +212,7 @@
  * Signal handler for SIGALRM.
  */
 static void
-timeout(int sig __unused)
+timeout(int sig)
 {
 
 	timed_out = 1;
@@ -234,10 +236,15 @@
 {
 	int fd;
 
-	if ((fd = open(name, O_RDONLY|O_EXLOCK, 0666)) == -1) {
+	if ((fd = open(name, O_RDONLY, 0666)) == -1) {
 		if (errno == ENOENT || errno == EINTR)
 			return;
 		err(EX_CANTCREAT, "cannot open %s", name);
+	}
+	if ((flock(fd, LOCK_EX)) == -1) {
+		if (errno == ENOENT || errno == EINTR)
+			return;
+		err(EX_CANTCREAT, "cannot lock %s", name);
 	}
 	close(fd);
 }