LibC: Implement tcflush(3)

Author: https://github.com/petelliott
Commit: https://github.com/SerenityOS/serenity/commit/7a27fa3df84
Pull-request: https://github.com/SerenityOS/serenity/pull/2758

Kernel/TTY/TTY.cpp

@@ -329,6 +329,14 @@ int TTY::ioctl(FileDescription&, unsigned request, FlatPtr arg)
         if (request == TCSETSF)
             flush_input();
         return 0;
+    case TCFLSH:
+        // Serenity's TTY implementation does not use an output buffer, so ignore TCOFLUSH.
+        if (arg == TCIFLUSH || arg == TCIOFLUSH) {
+            flush_input();
+        } else if (arg != TCOFLUSH) {
+            return -EINVAL;
+        }
+        return 0;
     case TIOCGWINSZ:
         ws = reinterpret_cast<winsize*>(arg);
         if (!current_process.validate_write(ws, sizeof(winsize)))

Libraries/LibC/sys/ioctl_numbers.h

@@ -52,6 +52,7 @@ enum IOCtlNumber {
     TCSETS,
     TCSETSW,
     TCSETSF,
+    TCFLSH,
     TIOCGWINSZ,
     TIOCSCTTY,
     TIOCNOTTY,
@@ -75,6 +76,7 @@ enum IOCtlNumber {
 #define TCSETS TCSETS
 #define TCSETSW TCSETSW
 #define TCSETSF TCSETSF
+#define TCFLSH TCFLSH
 #define TIOCGWINSZ TIOCGWINSZ
 #define TIOCSCTTY TIOCSCTTY
 #define TIOCNOTTY TIOCNOTTY

Libraries/LibC/termios.cpp

@@ -60,9 +60,7 @@ int tcflow(int fd, int action)
 
 int tcflush(int fd, int queue_selector)
 {
-    (void)fd;
-    (void)queue_selector;
-    ASSERT_NOT_REACHED();
+    return ioctl(fd, TCFLSH, queue_selector);
 }
 
 speed_t cfgetispeed(const struct termios* tp)