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SubjectRe: [PATCH 2/2] Input: Add EVIOC mechanism for MT slots
On 01/12/2012 08:24 PM, Henrik Rydberg wrote:
> 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.

>
> Cc: Chase Douglas <chase.douglas@canonical.com>
> Signed-off-by: Henrik Rydberg <rydberg@euromail.se>
> ---
> 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?

> + 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.

> + 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;
> + __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 */



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