terminal-util: move lock_dev_console() here

It doesn't really make sense to have that in dev-setup.c, which is
mostly about setting up /dev/, creating device nodes and stuff.

let's move it to the other stuff that deals with /dev/console's
peculiarities.

src/basic/terminal-util.c

@@ -618,6 +618,23 @@ void reset_dev_console_fd(int fd, bool switch_to_text) {
                 log_warning_errno(r, "Failed to reset /dev/console using ANSI sequences, ignoring: %m");
 }
 
+int lock_dev_console(void) {
+        _cleanup_close_ int fd = -EBADF;
+        int r;
+
+        /* NB: We do not use O_NOFOLLOW here, because some container managers might place a symlink to some
+         * pty in /dev/console, in which case it should be fine to lock the target TTY. */
+        fd = open_terminal("/dev/console", O_RDONLY|O_CLOEXEC|O_NOCTTY);
+        if (fd < 0)
+                return fd;
+
+        r = lock_generic(fd, LOCK_BSD, LOCK_EX);
+        if (r < 0)
+                return r;
+
+        return TAKE_FD(fd);
+}
+
 int make_console_stdio(void) {
         int fd, r;
 

src/basic/terminal-util.h

@@ -88,6 +88,7 @@ int vtnr_from_tty(const char *tty);
 const char* default_term_for_tty(const char *tty);
 
 void reset_dev_console_fd(int fd, bool switch_to_text);
+int lock_dev_console(void);
 int make_console_stdio(void);
 
 int fd_columns(int fd);