[PATCH v2 2/2] input/uinput: add UI_GET_SYSPATH ioctl to retrieve the sysfs path

[Benjamin Tissoires <benjamin.tissoires@redhat.com>]

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.

[1] http://www.freedesktop.org/wiki/Evemu/

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
---
 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@redhat.com>)
  *		- update uinput_user_dev struct to allow abs resolution
+ *		- add UI_GET_SYSPATH ioctl
  *	0.3	09/04/2006 (Anssi Hannula <anssi.hannula@gmail.com>)
  *		- 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)
+{
+	int len;
+
+	if (!str)
+		return -ENOENT;
+
+	len = strlen(str) + 1;
+	if (len > maxlen)
+		len = maxlen;
+
+	return copy_to_user(p, str, len) ? -EFAULT : len;
+}
+
 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);
+				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@redhat.com>)
  *		- 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@redhat.com>)
  *		- 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