linux-kernel - [PATCH v2] Input: evdev - Add EVIOC mechanism to extract the MT slot state

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Date:	Fri,  6 Jan 2012 16:16:59 +0100
From:	"Henrik Rydberg" <rydberg@...omail.se>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	Henrik Rydberg <rydberg@...omail.se>,
	Chase Douglas <chase.douglas@...onical.com>
Subject: [PATCH v2] Input: evdev - Add EVIOC mechanism to extract the MT slot state

This patch adds the ability to extract the MT slot state sequentially
via EVIOCGABS. The slot parameter is first selected by calling
EVIOCSABS with ABS_MT_SLOT as argument, followed by a set of EVIOCGABS
calls. The slot selection is local to the evdev client handler, and
does not affect the actual input state.

Cc: Chase Douglas <chase.douglas@...onical.com>
Signed-off-by: Henrik Rydberg <rydberg@...omail.se>
---
Hi Dmitry,

the first version of this patch was sent a long time ago (May 2010),
but was put on hold due to a lack of usecases. Now, it seems such a
case has arrived, in the X server (evdev). Some MT events may be much
less frequent than others (ABS_MT_ORIENTATION, for example), resulting
in wrong touch values being assumed after, say, an X restart.

I am not 100% in favor of this patch myself. Perhaps there should be a
more explicit mechanism for selecting slots, for instance.

The patch has been tested against both 3.2 and 3.1 stable.

Cheers,
Henrik

 drivers/input/evdev.c |   23 +++++++++++++++++++----
 1 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
index 4cf2534..4878e63 100644
--- a/drivers/input/evdev.c
+++ b/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"
@@ -46,6 +46,7 @@ struct evdev_client {
 	struct fasync_struct *fasync;
 	struct evdev *evdev;
 	struct list_head node;
+	int mt_slot;		/* used to extract MT events via EVIOC */
 	unsigned int bufsize;
 	struct input_event buffer[];
 };
@@ -621,6 +622,16 @@ static int evdev_handle_set_keycode_v2(struct input_dev *dev, void __user *p)
 	return input_set_keycode(dev, &ke);
 }
 
+static int evdev_get_abs_value(const struct evdev_client *client,
+			       const struct input_dev *dev, unsigned int code)
+{
+	if (code == ABS_MT_SLOT)
+		return client->mt_slot;
+	if (dev->mt && input_is_mt_axis(code))
+		return input_mt_get_value(&dev->mt[client->mt_slot], code);
+	return dev->absinfo[code].value;
+}
+
 static long evdev_do_ioctl(struct file *file, unsigned int cmd,
 			   void __user *p, int compat_mode)
 {
@@ -757,6 +768,7 @@ static long evdev_do_ioctl(struct file *file, unsigned int cmd,
 
 			t = _IOC_NR(cmd) & ABS_MAX;
 			abs = dev->absinfo[t];
+			abs.value = evdev_get_abs_value(client, dev, t);
 
 			if (copy_to_user(p, &abs, min_t(size_t,
 					size, sizeof(struct input_absinfo))))
@@ -782,9 +794,12 @@ static long evdev_do_ioctl(struct file *file, unsigned int cmd,
 			if (size < sizeof(struct input_absinfo))
 				abs.resolution = 0;
 
-			/* We can't change number of reserved MT slots */
-			if (t == ABS_MT_SLOT)
-				return -EINVAL;
+			/* Set the MT slot to return through EVIOCGABS */
+			if (t == ABS_MT_SLOT) {
+				if (abs.value >= 0 && abs.value < dev->mtsize)
+					client->mt_slot = abs.value;
+				return 0;
+			}
 
 			/*
 			 * Take event lock to ensure that we are not
-- 
1.7.8.1

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