[PATCH] Add setsid option to save child process id

Add an option to save the child's pid into a file.

Marc.

diff -NRapruz -X /etc/diff.excludes util-linux-2.40.4/sys-utils/setsid.1.adoc devel-2.40.4/sys-utils/setsid.1.adoc
--- util-linux-2.40.4/sys-utils/setsid.1.adoc
+++ devel-2.40.4/sys-utils/setsid.1.adoc
@@ -31,6 +31,9 @@ Always create a new process.
 *-w*, *--wait*::
 Wait for the execution of the program to end, and return the exit status of this program as the exit status of *setsid*.

+*-p*, *--pidfile* _file_::
+If forked, write the process id of the program to _file_.
+
 *-V*, *--version*::
 Display version information and exit.

diff -NRapruz -X /etc/diff.excludes util-linux-2.40.4/sys-utils/setsid.c devel-2.40.4/sys-utils/setsid.c
--- util-linux-2.40.4/sys-utils/setsid.c
+++ devel-2.40.4/sys-utils/setsid.c
@@ -14,6 +14,9 @@
  *
  * 2008-08-20 Daniel Kahn Gillmor <[email protected]>
  * - if forked, wait on child process and emit its return code.
+ *
+ * 2025-01-25 Marc Aurèle La France <[email protected]>
+ * - If forked, save the child's process id in a file.
  */
 #include <getopt.h>
 #include <stdio.h>
@@ -39,11 +42,12 @@ static void __attribute__((__noreturn__)) usage(void)
 	fputs(_("Run a program in a new session.\n"), out);

 	fputs(USAGE_OPTIONS, out);
-	fputs(_(" -c, --ctty     set the controlling terminal to the current one\n"), out);
-	fputs(_(" -f, --fork     always fork\n"), out);
-	fputs(_(" -w, --wait     wait program to exit, and use the same return\n"), out);
+	fputs(_(" -c, --ctty               set the controlling terminal to the current one\n"), out);
+	fputs(_(" -f, --fork               always fork\n"), out);
+	fputs(_(" -w, --wait               wait program to exit, and use the same return\n"), out);
+	fputs(_(" -p, --pidfile <file>     write child pid to <file>\n"), out);

-	fprintf(out, USAGE_HELP_OPTIONS(16));
+	fprintf(out, USAGE_HELP_OPTIONS(26));

 	fprintf(out, USAGE_MAN_TAIL("setsid(1)"));
 	exit(EXIT_SUCCESS);
@@ -55,14 +59,17 @@ int main(int argc, char **argv)
 	int ctty = 0;
 	pid_t pid;
 	int status = 0;
+	const char *pidpath = NULL;
+	FILE *pidfile;

 	static const struct option longopts[] = {
-		{"ctty", no_argument, NULL, 'c'},
-		{"fork", no_argument, NULL, 'f'},
-		{"wait", no_argument, NULL, 'w'},
-		{"version", no_argument, NULL, 'V'},
-		{"help", no_argument, NULL, 'h'},
-		{NULL, 0, NULL, 0}
+		{"ctty",    no_argument,       NULL, 'c'},
+		{"fork",    no_argument,       NULL, 'f'},
+		{"wait",    no_argument,       NULL, 'w'},
+		{"pidfile", required_argument, NULL, 'p'},
+		{"version", no_argument,       NULL, 'V'},
+		{"help",    no_argument,       NULL, 'h'},
+		{NULL,      0,                 NULL, 0}
 	};

 	setlocale(LC_ALL, "");
@@ -70,7 +77,7 @@ int main(int argc, char **argv)
 	textdomain(PACKAGE);
 	close_stdout_atexit();

-	while ((ch = getopt_long(argc, argv, "+Vhcfw", longopts, NULL)) != -1)
+	while ((ch = getopt_long(argc, argv, "+Vhcfp:w", longopts, NULL)) != -1)
 		switch (ch) {
 		case 'c':
 			ctty=1;
@@ -81,6 +88,9 @@ int main(int argc, char **argv)
 		case 'w':
 			status = 1;
 			break;
+		case 'p':
+			pidpath = optarg;
+			break;

 		case 'h':
 			usage();
@@ -105,6 +115,16 @@ int main(int argc, char **argv)
 			break;
 		default:
 			/* parent */
+			if (pidpath) {
+				pidfile = fopen(pidpath, "w");
+				if (pidfile == NULL)
+					warn(_("cannot open pidfile %s"),
+						pidpath);
+				else {
+					fprintf(pidfile, "%d\n", pid);
+					fclose(pidfile);
+				}
+			}
 			if (!status)
 				return EXIT_SUCCESS;
 			if (wait(&status) != pid)