On Fri, Jan 13, 2012 at 09:34:12AM +0100, Chase Douglas wrote:

On 01/12/2012 08:24 PM, Henrik Rydberg wrote:

quoted

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 { struct input_mt_request req; int values[64]; } data;
data.req.code = ABS_MT_POSITION_X;
if (ioctl(fd, EVIOCGMTSLOTS(sizeof(data)), &data) < 0)
	return -1;
for (i = 0; i < data.req.num_values; i++)
	printf("slot %d: %d\n", i, data.values[i]);

If input_mt_request is:

struct input_mt_request {
	__u32 code;
	__u32 num_values;
	__s32 values[];
};

then how passing in the data struct above work? The passed in data would be:

__u32 code;
__u32 num_values; /* BTW, this isn't set in the example above */
__s32 *values; /* This is left uninitialized in the example above */
int values[0]
int values[1]
int values[2]
...
int values[63]

I'm not too familiar with ioctl interfaces, but I don't see how this
example could work.

There isn't a separate __s32 *values pointer, the actual memory layout
from kernel's POV would be:

__u32 code;
__u32 num_values;
__s32 values[0];
__s32 values[1];
...
__s32 values[63];

quoted

Cc: Chase Douglas <redacted>
Signed-off-by: Henrik Rydberg <redacted>
---
Hi Dmitry,

This is a new take on the MT slot ioctl patch. A new ioctl is added,
which takes a request structure and returns a (variable) array of slot
values. The patch seems to work, but testing has not been extensive (yet).

Cheers,
Henrik

 drivers/input/evdev.c |   30 +++++++++++++++++++++++++++++-
 include/linux/input.h |   25 +++++++++++++++++++++++++
 2 files changed, 54 insertions(+), 1 deletions(-)

diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
index 4cf2534..8bf45d4 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"

@@ -621,6 +621,31 @@ 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 i;
+
+	if (get_user(code, &ip[0]))
+		return -EFAULT;
+	if (!input_is_mt_value(code))
+		return -EINVAL;
+
+	if (size < sizeof(struct input_mt_request) + dev->mtsize * sizeof(int))
+		return -EINVAL;

Why not fill in up to the size of the array provided?

Yes, I think we do the same with other ioctls as well.

quoted

+	if (put_user(dev->mtsize, &ip[1]))
+		return -EFAULT;
+	for (i = 0; i < dev->mtsize; i++)
+		if (put_user(input_mt_get_value(&mt[i], code), &ip[2 + i]))
+			return -EFAULT;

This would be easier to understand if you did:

struct input_mt_request *req = (struct input_mt_request *)ip;

Then modify the stuff in a straightforward way.

This is a user pointer, you can't really do it in straightforward way...

quoted

+	return 0;
+}
+
 static long evdev_do_ioctl(struct file *file, unsigned int cmd,
 			   void __user *p, int compat_mode)
 {

@@ -706,6 +731,9 @@ 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);
 

diff --git a/include/linux/input.h b/include/linux/input.h
index a637e78..9a73f18 100644
--- a/include/linux/input.h
+++ b/include/linux/input.h

@@ -99,6 +99,30 @@ struct input_keymap_entry {
 	__u8  scancode[32];
 };
 
+/**
+ * struct input_mt_request - used by EVIOCGMTSLOTS ioctl
+ * @code: ABS_MT code to read
+ * @num_values: number of values written to the value array
+ * @values: value array, one value per slot
+ *
+ * The structure is used to retrieve MT slot data. Before the call,
+ * code is set to the wanted ABS_MT event type. On return, the value
+ * array is filled with the slot values for the specified ABS_MT code,
+ * and num_values is set to the actual number of slots.
+ *
+ * The call argument (len) is the size of the return buffer, satisfying
+ *
+ * len >= sizeof(input_mt_request) + sizeof(__s32) * number_of_slots
+ *
+ * If the request code is not an ABS_MT value, or if len is too small,
+ * -EINVAL is returned.
+ */
+struct input_mt_request {
+	__u32 code;
+	__u32 num_values;

Hmm, might avoid this one... Userspace can do EVIOCGABS to get number of
slots and then it will know how much data EVIOCGMTSLOTS will return...

quoted

+	__s32 values[];
+};
+
 #define EVIOCGVERSION		_IOR('E', 0x01, int)			/* get driver version */
 #define EVIOCGID		_IOR('E', 0x02, struct input_id)	/* get device ID */
 #define EVIOCGREP		_IOR('E', 0x03, unsigned int[2])	/* get repeat settings */

@@ -113,6 +137,7 @@ struct input_keymap_entry {
 #define EVIOCGPHYS(len)		_IOC(_IOC_READ, 'E', 0x07, len)		/* get physical location */
 #define EVIOCGUNIQ(len)		_IOC(_IOC_READ, 'E', 0x08, len)		/* get unique identifier */
 #define EVIOCGPROP(len)		_IOC(_IOC_READ, 'E', 0x09, len)		/* get device properties */
+#define EVIOCGMTSLOTS(len)	_IOC(_IOC_READ, 'E', 0x0a, len)		/* get MT slot values */
 
 #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 */

Thanks.

-- 
Dmitry