Implement -o for flock(1) to close fd before exec

flock.1

@@ -6,7 +6,7 @@
 .Nd tool to manage locks on files
 .Sh SYNOPSIS
 .Nm
-.Op Fl nsux
+.Op Fl nosux
 .Ar file
 .Ar cmd Op arg ...
 .Sh DESCRIPTION
@@ -20,6 +20,9 @@ does not exist, it will be created.
 .It Fl n
 Set non-blocking mode on the lock.  Fail immediately if the lock
 cannot be acquired.
+.It Fl o
+Close the file descriptor before exec to avoid having the exec'ed
+program holding on to the lock.
 .It Fl s
 Acquire a shared lock.
 .It Fl u

flock.c

@@ -12,19 +12,22 @@
 static void
 usage(void)
 {
-	eprintf("usage: %s [-nsux] file cmd [arg ...]\n", argv0);
+	eprintf("usage: %s [-nosux] file cmd [arg ...]\n", argv0);
 }
 
 int
 main(int argc, char *argv[])
 {
-	int fd, status, savederrno, flags = LOCK_EX, nonblk = 0;
+	int fd, status, savederrno, flags = LOCK_EX, nonblk = 0, oflag = 0;
 	pid_t pid;
 
 	ARGBEGIN {
 	case 'n':
 		nonblk = LOCK_NB;
 		break;
+	case 'o':
+		oflag = 1;
+		break;
 	case 's':
 		flags = LOCK_SH;
 		break;
@@ -54,6 +57,8 @@ main(int argc, char *argv[])
 	case -1:
 		eprintf("fork:");
 	case 0:
+		if (oflag && close(fd) < 0)
+			eprintf("close:");
 		argv++;
 		execvp(*argv, argv);
 		savederrno = errno;