Input: Add EVIOC mechanism for MT slots

This patch adds the ability to extract MT slot data via a new ioctl,
EVIOCGMTSLOTS. The function returns an array of slot values for the
specified ABS_MT event type.

Example of user space usage:

struct { unsigned code; int values[64]; } req;
req.code = ABS_MT_POSITION_X;
if (ioctl(fd, EVIOCGMTSLOTS(sizeof(req)), &req) < 0)
	return -1;
for (i = 0; i < 64; i++)
	printf("slot %d: %d\n", i, req.values[i]);
Reviewed-by: Chase Douglas <chase.douglas@canonical.com>
Signed-off-by: Henrik Rydberg <rydberg@euromail.se>

drivers/input/evdev.c

@@ -20,7 +20,7 @@
 #include <linux/slab.h>
 #include <linux/module.h>
 #include <linux/init.h>
-#include <linux/input.h>
+#include <linux/input/mt.h>
 #include <linux/major.h>
 #include <linux/device.h>
 #include "input-compat.h"
@@ -623,6 +623,28 @@ static int evdev_handle_set_keycode_v2(struct input_dev *dev, void __user *p)
 	return input_set_keycode(dev, &ke);
 }
 
+static int evdev_handle_mt_request(struct input_dev *dev,
+				   unsigned int size,
+				   int __user *ip)
+{
+	const struct input_mt_slot *mt = dev->mt;
+	unsigned int code;
+	int max_slots;
+	int i;
+
+	if (get_user(code, &ip[0]))
+		return -EFAULT;
+	if (!input_is_mt_value(code))
+		return -EINVAL;
+
+	max_slots = (size - sizeof(__u32)) / sizeof(__s32);
+	for (i = 0; i < dev->mtsize && i < max_slots; i++)
+		if (put_user(input_mt_get_value(&mt[i], code), &ip[1 + i]))
+			return -EFAULT;
+
+	return 0;
+}
+
 static long evdev_do_ioctl(struct file *file, unsigned int cmd,
 			   void __user *p, int compat_mode)
 {
@@ -708,6 +730,9 @@ static long evdev_do_ioctl(struct file *file, unsigned int cmd,
 		return bits_to_user(dev->propbit, INPUT_PROP_MAX,
 				    size, p, compat_mode);
 
+	case EVIOCGMTSLOTS(0):
+		return evdev_handle_mt_request(dev, size, ip);
+
 	case EVIOCGKEY(0):
 		return bits_to_user(dev->key, KEY_MAX, size, p, compat_mode);
 

include/linux/input.h

@@ -114,6 +114,31 @@ struct input_keymap_entry {
 #define EVIOCGUNIQ(len)		_IOC(_IOC_READ, 'E', 0x08, len)		/* get unique identifier */
 #define EVIOCGPROP(len)		_IOC(_IOC_READ, 'E', 0x09, len)		/* get device properties */
 
+/**
+ * EVIOCGMTSLOTS(len) - get MT slot values
+ *
+ * The ioctl buffer argument should be binary equivalent to
+ *
+ * struct input_mt_request_layout {
+ *	__u32 code;
+ *	__s32 values[num_slots];
+ * };
+ *
+ * where num_slots is the (arbitrary) number of MT slots to extract.
+ *
+ * The ioctl size argument (len) is the size of the buffer, which
+ * should satisfy len = (num_slots + 1) * sizeof(__s32).  If len is
+ * too small to fit all available slots, the first num_slots are
+ * returned.
+ *
+ * Before the call, code is set to the wanted ABS_MT event type. On
+ * return, values[] is filled with the slot values for the specified
+ * ABS_MT code.
+ *
+ * If the request code is not an ABS_MT value, -EINVAL is returned.
+ */
+#define EVIOCGMTSLOTS(len)	_IOC(_IOC_READ, 'E', 0x0a, len)
+
 #define EVIOCGKEY(len)		_IOC(_IOC_READ, 'E', 0x18, len)		/* get global key state */
 #define EVIOCGLED(len)		_IOC(_IOC_READ, 'E', 0x19, len)		/* get all LEDs */
 #define EVIOCGSND(len)		_IOC(_IOC_READ, 'E', 0x1a, len)		/* get all sounds status */