Hi
On Fri, Jan 8, 2016 at 4:23 PM, Aniroop Mathur <a.mathur@xxxxxxxxxxx> wrote:
> Add ioctl cmd EVIOCGBUFSIZE to get kernel buffer size of device so that
> clients can accordingly set the size of userspace buffer and can know
> maximum number of events that they are required to read in worst case.
Why is that needed? What's wrong with resizing your buffers in
user-space? Exposing this information limits the kernel to never allow
dynamically sized buffers.
Furthermore, in user-space you don't have to pre-allocate your
buffers. It'd be enough to reserve the address space for it.
Could you elaborate on your use-case?
> Signed-off-by: Aniroop Mathur <a.mathur@xxxxxxxxxxx>
> ---
> drivers/input/evdev.c | 3 +++
> include/uapi/linux/input.h | 2 ++
> 2 files changed, 5 insertions(+)
>
> diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
> index e9ae3d5..8b16f08 100644
> --- a/drivers/input/evdev.c
> +++ b/drivers/input/evdev.c
> @@ -1103,6 +1103,9 @@ static long evdev_do_ioctl(struct file *file, unsigned int cmd,
>
> return 0;
>
> + case EVIOCGBUFSIZE:
> + return put_user(client->bufsize, (unsigned int __user *)p);
> +
> case EVIOCRMFF:
> return input_ff_erase(dev, (int)(unsigned long) p, file);
>
> diff --git a/include/uapi/linux/input.h b/include/uapi/linux/input.h
> index 2758687..51d66aa 100644
> --- a/include/uapi/linux/input.h
> +++ b/include/uapi/linux/input.h
> @@ -114,6 +114,8 @@ struct input_mask {
> #define EVIOCSKEYCODE _IOW('E', 0x04, unsigned int[2]) /* set keycode */
> #define EVIOCSKEYCODE_V2 _IOW('E', 0x04, struct input_keymap_entry)
>
> +#define EVIOCGBUFSIZE _IOR('E', 0x05, unsigned int) /* get device buffer size */
Please document all new ioctls. See EVIOCSMASK for an example.
Thanks
David
> +
> #define EVIOCGNAME(len) _IOC(_IOC_READ, 'E', 0x06, len) /* get device name */
> #define EVIOCGPHYS(len) _IOC(_IOC_READ, 'E', 0x07, len) /* get physical location */
> #define EVIOCGUNIQ(len) _IOC(_IOC_READ, 'E', 0x08, len) /* get unique identifier */
> --
> 1.7.9.5
>
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