[fork-tester.c] Get PPID from env MANAGERPID when systemd run with --…

…user

Fix [cilium#3148](cilium#3148)
On certain distributions, `systemd` run with the flag `--user`. This
means that the manager PID is not 1 but one of it's child process.
To fix this, we call the environment variable `MANAGERPID` set by systemd
that expose this PID

Signed-off-by: Tristan d'Audibert <[email protected]>

contrib/tester-progs/fork-tester.c

@@ -29,10 +29,20 @@ void child1()
 		perror("fork");
 		exit(1);
 	} else if (pid == 0) {
+		int manager_pid = 1; // systemd init PID
 		for (int i = 0;; i++) {
 			int ppid = getppid();
-			if (ppid == 1) {
+			if (ppid == manager_pid) {
 				break;
+			} else {
+				// If systemd run with --user
+				const char *manager_pid_str = getenv("MANAGERPID");
+				if (manager_pid_str) {
+					manager_pid = atoi(manager_pid_str);
+					if (ppid == manager_pid)
+						break;
+					manager_pid = 1;
+				}
 			}
 			if (i == 30) {
 				fprintf(stderr, "giving up on waiting our parent to die\n");