ttyprintk: Add TTY port shutdown callback

By adding the TTY port shutdown callback, the final buffer flush has
been moved from tpk_close() to tpk_port_shutdown(). This enables buffer
flush upon close and hangup as well. The change also removes the
specific 'buf == NULL' handling in tpk_printk(), which became useless.
Signed-off-by: Samo Pogačnik <samo_pogacnik@t-2.net>
Link: https://lore.kernel.org/r/f236ea26520fbef176fefec2e06a43548f63fa9c.camel@t-2.netSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/char/ttyprintk.c

@@ -54,11 +54,6 @@ static int tpk_printk(const unsigned char *buf, int count)
 {
 	int i = tpk_curr;
 
-	if (buf == NULL) {
-		tpk_flush();
-		return i;
-	}
-
 	for (i = 0; i < count; i++) {
 		if (tpk_curr >= TPK_STR_SIZE) {
 			/* end of tmp buffer reached: cut the message in two */
@@ -100,12 +95,6 @@ static int tpk_open(struct tty_struct *tty, struct file *filp)
 static void tpk_close(struct tty_struct *tty, struct file *filp)
 {
 	struct ttyprintk_port *tpkp = tty->driver_data;
-	unsigned long flags;
-
-	spin_lock_irqsave(&tpkp->spinlock, flags);
-	/* flush tpk_printk buffer */
-	tpk_printk(NULL, 0);
-	spin_unlock_irqrestore(&tpkp->spinlock, flags);
 
 	tty_port_close(&tpkp->port, tty, filp);
 }
@@ -168,6 +157,20 @@ static void tpk_hangup(struct tty_struct *tty)
 	tty_port_hangup(&tpkp->port);
 }
 
+/*
+ * TTY port operations shutdown function.
+ */
+static void tpk_port_shutdown(struct tty_port *tport)
+{
+	struct ttyprintk_port *tpkp =
+		container_of(tport, struct ttyprintk_port, port);
+	unsigned long flags;
+
+	spin_lock_irqsave(&tpkp->spinlock, flags);
+	tpk_flush();
+	spin_unlock_irqrestore(&tpkp->spinlock, flags);
+}
+
 static const struct tty_operations ttyprintk_ops = {
 	.open = tpk_open,
 	.close = tpk_close,
@@ -177,7 +180,9 @@ static const struct tty_operations ttyprintk_ops = {
 	.hangup = tpk_hangup,
 };
 
-static const struct tty_port_operations null_ops = { };
+static const struct tty_port_operations tpk_port_ops = {
+	.shutdown = tpk_port_shutdown,
+};
 
 static struct tty_driver *ttyprintk_driver;
 
@@ -195,7 +200,7 @@ static int __init ttyprintk_init(void)
 		return PTR_ERR(ttyprintk_driver);
 
 	tty_port_init(&tpk_port.port);
-	tpk_port.port.ops = &null_ops;
+	tpk_port.port.ops = &tpk_port_ops;
 
 	ttyprintk_driver->driver_name = "ttyprintk";
 	ttyprintk_driver->name = "ttyprintk";