Input: evdev - convert to dynamic event buffer

Allocate the event buffer dynamically, and prepare to compute the
buffer size in a separate function. This patch defines the size
computation to be identical to the current code, and does not contain
any logical changes.
Signed-off-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

drivers/input/evdev.c

@@ -10,7 +10,7 @@
 
 #define EVDEV_MINOR_BASE	64
 #define EVDEV_MINORS		32
-#define EVDEV_BUFFER_SIZE	64
+#define EVDEV_MIN_BUFFER_SIZE	64
 
 #include <linux/poll.h>
 #include <linux/sched.h>
@@ -36,13 +36,14 @@ struct evdev {
 };
 
 struct evdev_client {
-	struct input_event buffer[EVDEV_BUFFER_SIZE];
 	int head;
 	int tail;
 	spinlock_t buffer_lock; /* protects access to buffer, head and tail */
 	struct fasync_struct *fasync;
 	struct evdev *evdev;
 	struct list_head node;
+	int bufsize;
+	struct input_event buffer[];
 };
 
 static struct evdev *evdev_table[EVDEV_MINORS];
@@ -56,7 +57,7 @@ static void evdev_pass_event(struct evdev_client *client,
 	 */
 	spin_lock(&client->buffer_lock);
 	client->buffer[client->head++] = *event;
-	client->head &= EVDEV_BUFFER_SIZE - 1;
+	client->head &= client->bufsize - 1;
 	spin_unlock(&client->buffer_lock);
 
 	if (event->type == EV_SYN)
@@ -242,11 +243,17 @@ static int evdev_release(struct inode *inode, struct file *file)
 	return 0;
 }
 
+static unsigned int evdev_compute_buffer_size(struct input_dev *dev)
+{
+	return EVDEV_MIN_BUFFER_SIZE;
+}
+
 static int evdev_open(struct inode *inode, struct file *file)
 {
 	struct evdev *evdev;
 	struct evdev_client *client;
 	int i = iminor(inode) - EVDEV_MINOR_BASE;
+	unsigned int bufsize;
 	int error;
 
 	if (i >= EVDEV_MINORS)
@@ -263,12 +270,17 @@ static int evdev_open(struct inode *inode, struct file *file)
 	if (!evdev)
 		return -ENODEV;
 
-	client = kzalloc(sizeof(struct evdev_client), GFP_KERNEL);
+	bufsize = evdev_compute_buffer_size(evdev->handle.dev);
+
+	client = kzalloc(sizeof(struct evdev_client) +
+				bufsize * sizeof(struct input_event),
+			 GFP_KERNEL);
 	if (!client) {
 		error = -ENOMEM;
 		goto err_put_evdev;
 	}
 
+	client->bufsize = bufsize;
 	spin_lock_init(&client->buffer_lock);
 	client->evdev = evdev;
 	evdev_attach_client(evdev, client);
@@ -334,7 +346,7 @@ static int evdev_fetch_next_event(struct evdev_client *client,
 	have_event = client->head != client->tail;
 	if (have_event) {
 		*event = client->buffer[client->tail++];
-		client->tail &= EVDEV_BUFFER_SIZE - 1;
+		client->tail &= client->bufsize - 1;
 	}
 
 	spin_unlock_irq(&client->buffer_lock);