Input: uinput - add UI_GET_SYSNAME ioctl to retrieve the sysfs path

uinput is used in the xorg-integration-tests suite and in the wayland
test suite. These automated tests suites create many virtual input
devices and then hook something to read these newly created devices.

Currently, uinput does not provide the created input device, which means
that we rely 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 without any doubts the event node.

Signed-off-by: Benjamin Tissoires <[e-mail]>
Reviewed-by: David Herrmann <[e-mail]>
Signed-off-by: Dmitry Torokhov <[e-mail]>

drivers/input/misc/uinput.c

···
  * Author: Aristeu Sergio Rozanski Filho <[e-mail]>
  *
  * Changes/Revisions:
+ *	0.4	01/09/2014 (Benjamin Tissoires <[e-mail]>)
+ *		- add UI_GET_SYSNAME ioctl
  *	0.3	09/04/2006 (Anssi Hannula <[e-mail]>)
  *		- updated ff support for the changes in kernel interface
  *		- added MODULE_VERSION
···
 	__ret;						\
 })
 
+static int uinput_str_to_user(void __user *dest, const char *str,
+			      unsigned int maxlen)
+{
+	char __user *p = dest;
+	int len, ret;
+
+	if (!str)
+		return -ENOENT;
+
+	if (maxlen == 0)
+		return -EINVAL;
+
+	len = strlen(str) + 1;
+	if (len > maxlen)
+		len = maxlen;
+
+	ret = copy_to_user(p, str, len);
+	if (ret)
+		return -EFAULT;
+
+	/* force terminating '\0' */
+	ret = put_user(0, p + len - 1);
+	return ret ? -EFAULT : len;
+}
+
 static long uinput_ioctl_handler(struct file *file, unsigned int cmd,
 				 unsigned long arg, void __user *p)
 {
···
 	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)
···
 			req->retval = ff_erase.retval;
 			uinput_request_done(udev, req);
 			goto out;
+	}
+
+	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);
+		goto out;
 	}
 
 	retval = -EINVAL;

include/linux/uinput.h

···
  * Author: Aristeu Sergio Rozanski Filho <[e-mail]>
  *
  * Changes/Revisions:
+ *	0.4	01/09/2014 (Benjamin Tissoires <[e-mail]>)
+ *		- 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

include/uapi/linux/uinput.h

···
  * Author: Aristeu Sergio Rozanski Filho <[e-mail]>
  *
  * Changes/Revisions:
+ *	0.4	01/09/2014 (Benjamin Tissoires <[e-mail]>)
+ *		- 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
···
 #include <linux/types.h>
 #include <linux/input.h>
 
-#define UINPUT_VERSION		3
+#define UINPUT_VERSION		4
 
 
 struct uinput_ff_upload {
···
 #define UI_END_FF_UPLOAD	_IOW(UINPUT_IOCTL_BASE, 201, struct uinput_ff_upload)
 #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