lockf: add a -T option to terminate the child upon early abort

This is useful to avoid having the command running twice in the face of
the admin terminating the process.  Notably, if the -p option is not in
use (or can't be used, e.g., because we can't open the file for writing)
then this provides a nice alternative where one simply needs to send a
SIGTERM to the lockf(1) process associated with the lock file to clean
it all up.

Reviewed by:	des
Differential Revision:	https://reviews.freebsd.org/D51025

usr.bin/lockf/lockf.1

@@ -30,7 +30,7 @@
 .Nd execute a command while holding a file lock
 .Sh SYNOPSIS
 .Nm
-.Op Fl knpsw
+.Op Fl knpsTw
 .Op Fl t Ar seconds
 .Ar file
 .Ar command
@@ -136,6 +136,22 @@ This option will cause
 to open
 .Ar file
 for writing rather than reading.
+.It Fl T
+Upon receipt of a
+.Dv SIGTERM ,
+forward a
+.Dv SIGTERM
+along to the
+.Ar command
+before cleaning up the
+.Ar file
+and exiting.
+By default,
+.Nm
+effectively orphans the
+.Ar command
+after cleaning up the
+.Ar file .
 .It Fl t Ar seconds
 Specifies a timeout for waiting for the lock.
 By default,

usr.bin/lockf/lockf.c

@@ -35,6 +35,7 @@
 #include <limits.h>
 #include <signal.h>
 #include <stdatomic.h>
+#include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -64,6 +65,7 @@ static int lockfd = -1;
 static int keep;
 static int fdlock;
 static int status;
+static bool termchild;
 static volatile sig_atomic_t timed_out;
 
 /*
@@ -109,7 +111,7 @@ main(int argc, char **argv)
 	silent = keep = writepid = 0;
 	flags = O_CREAT | O_RDONLY;
 	waitsec = -1;	/* Infinite. */
-	while ((ch = getopt(argc, argv, "knpst:w")) != -1) {
+	while ((ch = getopt(argc, argv, "knpsTt:w")) != -1) {
 		switch (ch) {
 		case 'k':
 			keep = 1;
@@ -120,6 +122,9 @@ main(int argc, char **argv)
 		case 's':
 			silent = 1;
 			break;
+		case 'T':
+			termchild = true;
+			break;
 		case 't':
 		{
 			const char *errstr;
@@ -356,6 +361,8 @@ static void
 killed(int sig)
 {
 
+	if (termchild && child >= 0)
+		kill(child, sig);
 	cleanup();
 	signal(sig, SIG_DFL);
 	if (kill(getpid(), sig) == -1)