Add option to lockf to avoid creating a file if it does not exist.

PR:	bin/170775
Submitted by:	Matthew Story <matthewstory@gmail.com>
Reviewed by:	scottl
MFC after:	1 week

2 files changed, 28 insertions, 8 deletions

diff --git a/usr.bin/lockf/lockf.1 b/usr.bin/lockf/lockf.1
index f3ad6df..be9d9cc 100644
--- a/usr.bin/lockf/lockf.1
+++ b/usr.bin/lockf/lockf.1
@@ -32,7 +32,7 @@
 .Nd execute a command while holding a file lock
 .Sh SYNOPSIS
 .Nm
-.Op Fl ks
+.Op Fl kns
 .Op Fl t Ar seconds
 .Ar file
 .Ar command
@@ -90,6 +90,18 @@ Causes
 .Nm
 to operate silently.
 Failure to acquire the lock is indicated only in the exit status.
+.It Fl n
+Causes
+.Nm
+to fail if the specified lock
+.Ar file
+does not exist. If
+.Fl n
+is not specified,
+.Nm
+will create
+.Ar file
+if necessary.
 .It Fl t Ar seconds
 Specifies a timeout for waiting for the lock.
 By default,
@@ -130,6 +142,10 @@ The
 utility
 was unable to create the lock file, e.g., because of insufficient access
 privileges.
+.It Dv EX_UNAVAILABLE
+The
+.Fl n
+option is specified and the specified lock file does not exist.
 .It Dv EX_USAGE
 There was an error on the
 .Nm
diff --git a/usr.bin/lockf/lockf.c b/usr.bin/lockf/lockf.c
index 368eed0..9a6141f 100644
--- a/usr.bin/lockf/lockf.c
+++ b/usr.bin/lockf/lockf.c
@@ -56,16 +56,20 @@ static volatile sig_atomic_t timed_out;
 int
 main(int argc, char **argv)
 {
-	int ch, silent, status, waitsec;
+	int ch, flags, silent, status, waitsec;
 	pid_t child;
 
 	silent = keep = 0;
+	flags = O_CREAT;
 	waitsec = -1;	/* Infinite. */
-	while ((ch = getopt(argc, argv, "skt:")) != -1) {
+	while ((ch = getopt(argc, argv, "sknt:")) != -1) {
 		switch (ch) {
 		case 'k':
 			keep = 1;
 			break;
+		case 'n':
+			flags &= ~O_CREAT;
+			break;
 		case 's':
 			silent = 1;
 			break;
@@ -118,13 +122,13 @@ main(int argc, char **argv)
 	 * avoiding the separate step of waiting for the lock.  This
 	 * yields fairness and improved performance.
 	 */
-	lockfd = acquire_lock(lockname, O_NONBLOCK);
+	lockfd = acquire_lock(lockname, flags | O_NONBLOCK);
 	while (lockfd == -1 && !timed_out && waitsec != 0) {
 		if (keep)
-			lockfd = acquire_lock(lockname, 0);
+			lockfd = acquire_lock(lockname, flags);
 		else {
 			wait_for_lock(lockname);
-			lockfd = acquire_lock(lockname, O_NONBLOCK);
+			lockfd = acquire_lock(lockname, flags | O_NONBLOCK);
 		}
 	}
 	if (waitsec > 0)
@@ -165,7 +169,7 @@ acquire_lock(const char *name, int flags)
 {
 	int fd;
 
-	if ((fd = open(name, O_RDONLY|O_CREAT|O_EXLOCK|flags, 0666)) == -1) {
+	if ((fd = open(name, flags|O_RDONLY|O_EXLOCK|flags, 0666)) == -1) {
 		if (errno == EAGAIN || errno == EINTR)
 			return (-1);
 		err(EX_CANTCREAT, "cannot open %s", name);
@@ -215,7 +219,7 @@ usage(void)
 {
 
 	fprintf(stderr,
-	    "usage: lockf [-ks] [-t seconds] file command [arguments]\n");
+	    "usage: lockf [-kns] [-t seconds] file command [arguments]\n");
 	exit(EX_USAGE);
 }