process-util: add new FORK_NEW_MOUNTNS flag to safe_fork()

That way we can move one more code location to use safe_fork()

src/basic/process-util.c

@@ -1199,7 +1199,10 @@ int safe_fork_full(
                 if (sigprocmask(SIG_SETMASK, &ss, &saved_ss) < 0)
                         return log_full_errno(prio, errno, "Failed to set signal mask: %m");
 
-        pid = fork();
+        if (flags & FORK_NEW_MOUNTNS)
+                pid = raw_clone(SIGCHLD|CLONE_NEWNS);
+        else
+                pid = fork();
         if (pid < 0) {
                 r = -errno;
 

src/basic/process-util.h

@@ -168,6 +168,7 @@ typedef enum ForkFlags {
         FORK_REOPEN_LOG    = 1U << 4,
         FORK_LOG           = 1U << 5,
         FORK_WAIT          = 1U << 6,
+        FORK_NEW_MOUNTNS   = 1U << 7,
 } ForkFlags;
 
 int safe_fork_full(const char *name, const int except_fds[], size_t n_except_fds, ForkFlags flags, pid_t *ret_pid);