hvc_console: Add support for tty window resizing

The patch provides the hvc_resize() function to update the terminal
window dimensions (struct winsize) for a specified hvc console.
The function stores the new window size and schedules a function
that finally updates the tty winsize and signals the change to
user space (SIGWINCH).
Because the winsize update must acquire a mutex and might sleep,
the function is scheduled instead of being called from hvc_poll()
or khvcd.

This patch uses the tty_do_resize() routine from the tty layer.
A pending resize work is canceled in hvc_close() and hvc_hangup().

Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

drivers/char/hvc_console.c

@@ -374,6 +374,9 @@ static void hvc_close(struct tty_struct *tty, struct file * filp)
 		if (hp->ops->notifier_del)
 			hp->ops->notifier_del(hp, hp->data);
 
+		/* cancel pending tty resize work */
+		cancel_work_sync(&hp->tty_resize);
+
 		/*
 		 * Chain calls chars_in_buffer() and returns immediately if
 		 * there is no buffered data otherwise sleeps on a wait queue
@@ -399,6 +402,9 @@ static void hvc_hangup(struct tty_struct *tty)
 	if (!hp)
 		return;
 
+	/* cancel pending tty resize work */
+	cancel_work_sync(&hp->tty_resize);
+
 	spin_lock_irqsave(&hp->lock, flags);
 
 	/*
@@ -494,6 +500,39 @@ static int hvc_write(struct tty_struct *tty, const unsigned char *buf, int count
 	return written;
 }
 
+/**
+ * hvc_set_winsz() - Resize the hvc tty terminal window.
+ * @work:	work structure.
+ *
+ * The routine shall not be called within an atomic context because it
+ * might sleep.
+ *
+ * Locking:	hp->lock
+ */
+static void hvc_set_winsz(struct work_struct *work)
+{
+	struct hvc_struct *hp;
+	unsigned long hvc_flags;
+	struct tty_struct *tty;
+	struct winsize ws;
+
+	hp = container_of(work, struct hvc_struct, tty_resize);
+	if (!hp)
+		return;
+
+	spin_lock_irqsave(&hp->lock, hvc_flags);
+	if (!hp->tty) {
+		spin_unlock_irqrestore(&hp->lock, hvc_flags);
+		return;
+	}
+	ws  = hp->ws;
+	tty = tty_kref_get(hp->tty);
+	spin_unlock_irqrestore(&hp->lock, hvc_flags);
+
+	tty_do_resize(tty, tty, &ws);
+	tty_kref_put(tty);
+}
+
 /*
  * This is actually a contract between the driver and the tty layer outlining
  * how much write room the driver can guarantee will be sent OR BUFFERED.  This
@@ -638,6 +677,24 @@ int hvc_poll(struct hvc_struct *hp)
 }
 EXPORT_SYMBOL_GPL(hvc_poll);
 
+/**
+ * hvc_resize() - Update terminal window size information.
+ * @hp:		HVC console pointer
+ * @ws:		Terminal window size structure
+ *
+ * Stores the specified window size information in the hvc structure of @hp.
+ * The function schedule the tty resize update.
+ *
+ * Locking:	Locking free; the function MUST be called holding hp->lock
+ */
+void hvc_resize(struct hvc_struct *hp, struct winsize ws)
+{
+	if ((hp->ws.ws_row != ws.ws_row) || (hp->ws.ws_col != ws.ws_col)) {
+		hp->ws = ws;
+		schedule_work(&hp->tty_resize);
+	}
+}
+
 /*
  * This kthread is either polling or interrupt driven.  This is determined by
  * calling hvc_poll() who determines whether a console adapter support
@@ -720,6 +777,7 @@ struct hvc_struct __devinit *hvc_alloc(uint32_t vtermno, int data,
 
 	kref_init(&hp->kref);
 
+	INIT_WORK(&hp->tty_resize, hvc_set_winsz);
 	spin_lock_init(&hp->lock);
 	spin_lock(&hvc_structs_lock);
 

drivers/char/hvc_console.h

@@ -27,6 +27,7 @@
 #ifndef HVC_CONSOLE_H
 #define HVC_CONSOLE_H
 #include <linux/kref.h>
+#include <linux/tty.h>
 
 /*
  * This is the max number of console adapters that can/will be found as
@@ -56,6 +57,8 @@ struct hvc_struct {
 	struct hv_ops *ops;
 	int irq_requested;
 	int data;
+	struct winsize ws;
+	struct work_struct tty_resize;
 	struct list_head next;
 	struct kref kref; /* ref count & hvc_struct lifetime */
 };
@@ -84,6 +87,9 @@ extern int __devexit hvc_remove(struct hvc_struct *hp);
 int hvc_poll(struct hvc_struct *hp);
 void hvc_kick(void);
 
+/* Resize hvc tty terminal window */
+extern void hvc_resize(struct hvc_struct *hp, struct winsize ws);
+
 /* default notifier for irq based notification */
 extern int notifier_add_irq(struct hvc_struct *hp, int data);
 extern void notifier_del_irq(struct hvc_struct *hp, int data);