diff: prefer posix_spawn over pdfork/execl

MFC After:		1 week
Reviewed by:		kib
Differential Revision:	https://reviews.freebsd.org/D56076

usr.bin/diff/pr.c

@@ -29,8 +29,10 @@
 
 #include <err.h>
 #include <errno.h>
+#include <fcntl.h>
 #include <paths.h>
 #include <signal.h>
+#include <spawn.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
@@ -41,6 +43,8 @@
 
 #define _PATH_PR "/usr/bin/pr"
 
+extern char **environ;
+
 struct pr *
 start_pr(char *file1, char *file2)
 {
@@ -48,6 +52,9 @@ start_pr(char *file1, char *file2)
 	pid_t pid;
 	char *header;
 	struct pr *pr;
+	posix_spawn_file_actions_t fa;
+	posix_spawnattr_t sa;
+	int error;
 
 	pr = xcalloc(1, sizeof(*pr));
 
@@ -56,19 +63,29 @@ start_pr(char *file1, char *file2)
 	fflush(stdout);
 	if (pipe(pfd) == -1)
 		err(2, "pipe");
-	switch ((pid = pdfork(&pr->procd, PD_CLOEXEC))) {
-	case -1:
-		err(2, "No more processes");
-	case 0:
-		/* child */
+
+	if ((error = posix_spawnattr_init(&sa)) != 0)
+		errc(2, error, "posix_spawnattr_init");
+	if ((error = posix_spawn_file_actions_init(&fa)) != 0)
+		errc(2, error, "posix_spawn_file_actions_init");
+
+	posix_spawnattr_setprocdescp_np(&sa, &pr->procd, 0);
+
 	if (pfd[0] != STDIN_FILENO) {
-			dup2(pfd[0], STDIN_FILENO);
-			close(pfd[0]);
+		posix_spawn_file_actions_adddup2(&fa, pfd[0], STDIN_FILENO);
+		posix_spawn_file_actions_addclose(&fa, pfd[0]);
 	}
-		close(pfd[1]);
-		execl(_PATH_PR, _PATH_PR, "-h", header, (char *)0);
-		_exit(127);
-	default:
+	posix_spawn_file_actions_addclose(&fa, pfd[1]);
+
+	char *argv[] = { __DECONST(char *, _PATH_PR),
+	    __DECONST(char *, "-h"), header, NULL };
+	error = posix_spawn(&pid, _PATH_PR, &fa, &sa, argv, environ);
+	if (error != 0)
+		errc(2, error, "could not spawn pr");
+
+	posix_spawn_file_actions_destroy(&fa);
+	posix_spawnattr_destroy(&sa);
+
 	/* parent */
 	if (pfd[1] == STDOUT_FILENO) {
 		pr->ostdout = STDOUT_FILENO;
@@ -81,7 +98,6 @@ start_pr(char *file1, char *file2)
 	}
 	close(pfd[0]);
 	free(header);
-	}
 	return (pr);
 }