*: introduce and use xfork() and xvfork()

function                                             old     new   delta
launch_helper                                        170     169      -1
setup_heredoc                                        312     302     -10
handle_dir_common                                    367     354     -13
expand_vars_to_list                                 2456    2443     -13
open_transformer                                      89      74     -15
data_extract_to_command                              439     423     -16
do_ipaddr                                           1406    1389     -17
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/7 up/down: 0/-85)             Total: -85 bytes

Signed-off-by: Pascal Bellard <pascal.bellard@ads-lu.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/networking/ftpd.c b/networking/ftpd.c
index c63b931..e8cae0a 100644
--- a/networking/ftpd.c
+++ b/networking/ftpd.c
@@ -632,10 +632,7 @@
 	xpiped_pair(outfd);
 
 	/*fflush_all(); - so far we dont use stdio on output */
-	pid = BB_MMU ? fork() : vfork();
-	if (pid < 0)
-		bb_perror_msg_and_die(BB_MMU ? "fork" : "vfork");
-
+	pid = BB_MMU ? xfork() : xvfork();
 	if (pid == 0) {
 		/* child */
 #if !BB_MMU
diff --git a/networking/ifupdown.c b/networking/ifupdown.c
index 1bab2c5..69c56e8 100644
--- a/networking/ifupdown.c
+++ b/networking/ifupdown.c
@@ -1041,12 +1041,10 @@
 	xpiped_pair(outfd);
 
 	fflush_all();
-	pid = vfork();
+	pid = xvfork();
 
-	switch (pid) {
-	case -1:  /* failure */
-		bb_perror_msg_and_die("vfork");
-	case 0:  /* child */
+	if (pid == 0) {
+		/* Child */
 		/* NB: close _first_, then move fds! */
 		close(infd.wr);
 		close(outfd.rd);
diff --git a/networking/inetd.c b/networking/inetd.c
index 2b0e006..7030062 100644
--- a/networking/inetd.c
+++ b/networking/inetd.c
@@ -1271,7 +1271,7 @@
 					pid = vfork();
 
 				if (pid < 0) { /* fork error */
-					bb_perror_msg("fork");
+					bb_perror_msg("vfork"+1);
 					sleep(1);
 					restore_sigmask(&omask);
 					maybe_close(accepted_fd);
diff --git a/networking/nc.c b/networking/nc.c
index 5fd8bd7..0dacaf1 100644
--- a/networking/nc.c
+++ b/networking/nc.c
@@ -216,10 +216,8 @@
 	if (execparam) {
 		pid_t pid;
 		/* With more than one -l, repeatedly act as server */
-		if (do_listen > 1 && (pid = vfork()) != 0) {
-			/* parent or error */
-			if (pid < 0)
-				bb_perror_msg_and_die("vfork");
+		if (do_listen > 1 && (pid = xvfork()) != 0) {
+			/* parent */
 			/* prevent zombies */
 			signal(SIGCHLD, SIG_IGN);
 			close(cfd);