Re: [PATCH v2 2/2] input/uinput: add UI_GET_SYSPATH ioctl to retrievethe sysfs path

[David Herrmann]

Hi

On Mon, Jul 15, 2013 at 3:37 PM, Benjamin Tissoires
<benjamin.tissoires@xxxxxxxxxx> wrote:
> Evemu [1] uses uinput to replay devices traces it has recorded. However,
> the way evemu uses uinput is slightly different from how uinput is
> supposed to be used.
> Evemu creates the device node through uinput, bu inject events through
> the input device node directly (and skipping the uinput node).
>
> Currently, evemu relies on an heuristic to guess which input node was
> created. The problem is that is heuristic is subjected to races between
> different uinput devices or even with physical devices. Having a way
> to retrieve the sysfs path allows us to find the event node without
> having to rely on this heuristic.

It would actually be enough to return the "input_no" from
input_register_device() (which is currently local but we could save it
in "dev"). Or only the device-name. I don't know why you want the full
syspath. It's just overhead in the kernel that we could easily let
user-space do. And the path /sys/class/input/<devname> can be put
together by user-space.

Anyway, Dmitry has to decide on that. Apart from some style-issues I
mentioned below:
  Reviewed-by: David Herrmann <dh.herrmann@xxxxxxxxx>

Cheers
David

> [1] http://www.freedesktop.org/wiki/Evemu/
>
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@xxxxxxxxxx>
> ---
>  drivers/input/misc/uinput.c | 37 ++++++++++++++++++++++++++++++++++++-
>  include/linux/uinput.h      |  1 +
>  include/uapi/linux/uinput.h |  3 +++
>  3 files changed, 40 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/input/misc/uinput.c b/drivers/input/misc/uinput.c
> index 7d518b4..49a9f7d 100644
> --- a/drivers/input/misc/uinput.c
> +++ b/drivers/input/misc/uinput.c
> @@ -22,6 +22,7 @@
>   * Changes/Revisions:
>   *     0.4     12/07/2013 (Peter Hutterer <peter.hutterer@xxxxxxxxxx>)
>   *             - update uinput_user_dev struct to allow abs resolution
> + *             - add UI_GET_SYSPATH ioctl

What tree is that patch against? I cannot see an "0.4" entry in:
http://git.kernel.org/cgit/linux/kernel/git/dtor/input.git/tree/drivers/input/misc/uinput.c?h=next

>   *     0.3     09/04/2006 (Anssi Hannula <anssi.hannula@xxxxxxxxx>)
>   *             - updated ff support for the changes in kernel interface
>   *             - added MODULE_VERSION
> @@ -667,6 +668,21 @@ static int uinput_ff_upload_from_user(const char __user *buffer,
>         __ret;                                          \
>  })
>
> +static int uinput_str_to_user(const char *str, unsigned int maxlen,
> +                             void __user *p)

As Peter mentioned, I'd move "maxlen" to the end.

> +{
> +       int len;
> +
> +       if (!str)
> +               return -ENOENT;
> +
> +       len = strlen(str) + 1;
> +       if (len > maxlen)
> +               len = maxlen;
> +
> +       return copy_to_user(p, str, len) ? -EFAULT : len;

I'd prefer a "strlcpy()" so we guarantee a terminating 0 for
user-space, but I guess that'd be rather complex to do here. I
couldn't find any strlcpy_to_user()...

> +}
> +
>  static long uinput_ioctl_handler(struct file *file, unsigned int cmd,
>                                  unsigned long arg, void __user *p)
>  {
> @@ -676,6 +692,8 @@ static long uinput_ioctl_handler(struct file *file, unsigned int cmd,
>         struct uinput_ff_erase  ff_erase;
>         struct uinput_request   *req;
>         char                    *phys;
> +       const char              *path;
> +       unsigned int            size;
>
>         retval = mutex_lock_interruptible(&udev->mutex);
>         if (retval)
> @@ -828,7 +846,24 @@ static long uinput_ioctl_handler(struct file *file, unsigned int cmd,
>                         break;
>
>                 default:
> -                       retval = -EINVAL;
> +                       retval = -EAGAIN;
> +       }
> +
> +       if (retval == -EAGAIN) {
> +               size = _IOC_SIZE(cmd);
> +
> +               /* Now check variable-length commands */
> +               switch (cmd & ~IOCSIZE_MASK) {
> +                       case UI_GET_SYSPATH(0):
> +                               path = kobject_get_path(&udev->dev->dev.kobj,
> +                                                       GFP_KERNEL);

I know, device registration is protected by udev->mutex but I'd still prefer:
  if (udev->state != UIST_CREATED)
    return -ENOENT;

But that's probably a matter of taste.

> +                               retval = uinput_str_to_user(path, size, p);
> +                               kfree(path);
> +                               break;
> +
> +                       default:
> +                               retval = -EINVAL;
> +               }
>         }
>
>   out:
> diff --git a/include/linux/uinput.h b/include/linux/uinput.h
> index 6291a22..64fab81 100644
> --- a/include/linux/uinput.h
> +++ b/include/linux/uinput.h
> @@ -22,6 +22,7 @@
>   * Changes/Revisions:
>   *     0.4     12/07/2013 (Peter Hutterer <peter.hutterer@xxxxxxxxxx>)
>   *             - update uinput_user_dev struct to allow abs resolution
> + *             - add UI_GET_SYSPATH ioctl
>   *     0.3     24/05/2006 (Anssi Hannula <anssi.hannulagmail.com>)
>   *             - update ff support for the changes in kernel interface
>   *             - add UINPUT_VERSION
> diff --git a/include/uapi/linux/uinput.h b/include/uapi/linux/uinput.h
> index f6a393b..d826409 100644
> --- a/include/uapi/linux/uinput.h
> +++ b/include/uapi/linux/uinput.h
> @@ -22,6 +22,7 @@
>   * Changes/Revisions:
>   *     0.4     12/07/2013 (Peter Hutterer <peter.hutterer@xxxxxxxxxx>)
>   *             - update uinput_user_dev struct to allow abs resolution
> + *             - add UI_GET_SYSPATH ioctl
>   *     0.3     24/05/2006 (Anssi Hannula <anssi.hannulagmail.com>)
>   *             - update ff support for the changes in kernel interface
>   *             - add UINPUT_VERSION
> @@ -75,6 +76,8 @@ struct uinput_ff_erase {
>  #define UI_BEGIN_FF_ERASE      _IOWR(UINPUT_IOCTL_BASE, 202, struct uinput_ff_erase)
>  #define UI_END_FF_ERASE                _IOW(UINPUT_IOCTL_BASE, 203, struct uinput_ff_erase)
>
> +#define UI_GET_SYSPATH(len)    _IOC(_IOC_READ, UINPUT_IOCTL_BASE, 300, len)
> +
>  /*
>   * To write a force-feedback-capable driver, the upload_effect
>   * and erase_effect callbacks in input_dev must be implemented.
> --
> 1.8.3.1
>
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