Re: [PATCH v3] input/uinput: add UI_GET_SYSNAME ioctl to retrieve thesysfs path

[David Herrmann]

Hi

On Fri, Jan 17, 2014 at 8:12 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 relies on libevdev, which creates the device node through uinput.
> It then injects events through the input device node directly (and it
> completely skips the uinput node).
>
> Currently, libevdev 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.
>
> [1] http://www.freedesktop.org/wiki/Evemu/
>
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@xxxxxxxxxx>
> ---
>
> Ok, I am resurrecting this. The original patch was sent last July here:
> https://patchwork.kernel.org/patch/2827524/
>
> changes since v2:
> - the ioctl returns only the device name, thus I renamed the ioctl to UI_GET_SYSNAME
> - reordered uinput_str_to_user() arguments
> - be sure to terminate the user string we send by \0
> - abort if udev->state is not UIST_CREATED
> - dropped the patch 1/2 (adding resolution to uinput) because I think David has
>   already it in one of his queues (ABS2 IIRC)
>
> I also posted the corresponding libevdev here:
> http://lists.freedesktop.org/archives/input-tools/2014-January/000757.html
>
> Cheers,
> Benjamin
>
>  drivers/input/misc/uinput.c | 46 ++++++++++++++++++++++++++++++++++++++++++++-
>  include/linux/uinput.h      |  2 ++
>  include/uapi/linux/uinput.h | 13 ++++++++++++-
>  3 files changed, 59 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/input/misc/uinput.c b/drivers/input/misc/uinput.c
> index 7728359..0203219 100644
> --- a/drivers/input/misc/uinput.c
> +++ b/drivers/input/misc/uinput.c
> @@ -20,6 +20,8 @@
>   * Author: Aristeu Sergio Rozanski Filho <aris@xxxxxxxxxxxxxxxxx>
>   *
>   * Changes/Revisions:
> + *     0.4     01/09/2014 (Benjamin Tissoires <benjamin.tissoires@xxxxxxxxxx>)
> + *             - add UI_GET_SYSNAME ioctl
>   *     0.3     09/04/2006 (Anssi Hannula <anssi.hannula@xxxxxxxxx>)
>   *             - updated ff support for the changes in kernel interface
>   *             - added MODULE_VERSION
> @@ -670,6 +672,27 @@ static int uinput_ff_upload_from_user(const char __user *buffer,
>         __ret;                                          \
>  })
>
> +static int uinput_str_to_user(void __user *dest, const char *str,
> +                             unsigned int maxlen)
> +{
> +       int len, ret;
> +
> +       if (!str)
> +               return -ENOENT;
> +
> +       len = strlen(str) + 1;
> +       if (len > maxlen)
> +               len = maxlen;
> +
> +       ret = copy_to_user(dest, str, len);
> +       if (ret)
> +               return -EFAULT;
> +
> +       /* force terminating '\0' */
> +       ret = copy_to_user(dest + len - 1, "\0", 1);

You must make sure "maxlen != 0", otherwise you write beyond buffer
boundaries here. I'd say return -EINVAL in case maxlen == 0.

btw., you can also use: put_user(0, (char*)dest + len - 1);

> +       return ret ? -EFAULT : len;
> +}
> +
>  static long uinput_ioctl_handler(struct file *file, unsigned int cmd,
>                                  unsigned long arg, void __user *p)
>  {
> @@ -679,6 +702,8 @@ 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              *name;
> +       unsigned int            size;
>
>         retval = mutex_lock_interruptible(&udev->mutex);
>         if (retval)
> @@ -831,7 +856,26 @@ static long uinput_ioctl_handler(struct file *file, unsigned int cmd,
>                         break;
>
>                 default:
> -                       retval = -EINVAL;
> +                       retval = -EAGAIN;
> +       }
> +
> +       if (retval == -EAGAIN) {

Ehh, in case another ioctl returns -EAGAIN, we overwrite the error
with -EINVAL below in the "default:" clause. Maybe we should first
convert all the "break;" commands to "goto out;".

Patch looks good to me.
Thanks
David

> +               size = _IOC_SIZE(cmd);
> +
> +               /* Now check variable-length commands */
> +               switch (cmd & ~IOCSIZE_MASK) {
> +                       case UI_GET_SYSNAME(0):
> +                               if (udev->state != UIST_CREATED) {
> +                                       retval = -ENOENT;
> +                                       goto out;
> +                               }
> +                               name = dev_name(&udev->dev->dev);
> +                               retval = uinput_str_to_user(p, name, size);
> +                               break;
> +
> +                       default:
> +                               retval = -EINVAL;
> +               }
>         }
>
>   out:
> diff --git a/include/linux/uinput.h b/include/linux/uinput.h
> index 0a4487d..0994c0d 100644
> --- a/include/linux/uinput.h
> +++ b/include/linux/uinput.h
> @@ -20,6 +20,8 @@
>   * Author: Aristeu Sergio Rozanski Filho <aris@xxxxxxxxxxxxxxxxx>
>   *
>   * Changes/Revisions:
> + *     0.4     01/09/2014 (Benjamin Tissoires <benjamin.tissoires@xxxxxxxxxx>)
> + *             - add UI_GET_SYSNAME 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 fe46431..0389b48 100644
> --- a/include/uapi/linux/uinput.h
> +++ b/include/uapi/linux/uinput.h
> @@ -20,6 +20,8 @@
>   * Author: Aristeu Sergio Rozanski Filho <aris@xxxxxxxxxxxxxxxxx>
>   *
>   * Changes/Revisions:
> + *     0.4     01/09/2014 (Benjamin Tissoires <benjamin.tissoires@xxxxxxxxxx>)
> + *             - add UI_GET_SYSNAME ioctl
>   *     0.3     24/05/2006 (Anssi Hannula <anssi.hannulagmail.com>)
>   *             - update ff support for the changes in kernel interface
>   *             - add UINPUT_VERSION
> @@ -35,7 +37,7 @@
>  #include <linux/types.h>
>  #include <linux/input.h>
>
> -#define UINPUT_VERSION         3
> +#define UINPUT_VERSION         4
>
>
>  struct uinput_ff_upload {
> @@ -73,6 +75,15 @@ 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)
>
> +/**
> + * UI_GET_SYSNAME - get the sysfs name of the created uinput device
> + *
> + * @return the sysfs name of the created virtual input device.
> + * The complete sysfs path is then /sys/devices/virtual/input/--NAME--
> + * Usually, it is in the form "inputN"
> + */
> +#define UI_GET_SYSNAME(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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