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>

2 files changed, 64 insertions, 0 deletions

diff --git a/drivers/char/hvc_console.c b/drivers/char/hvc_console.c
index 3650c904401e..2d256dc80529 100644
--- a/drivers/char/hvc_console.c
+++ b/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);
 
diff --git a/drivers/char/hvc_console.h b/drivers/char/hvc_console.h
index ec0e9bb0e5e6..e3359f3c9b2a 100644
--- a/drivers/char/hvc_console.h
+++ b/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);