[PATCH] evdev: add phys property (EVIOCGPHYS) as stable identifier

[Peter Korsgaard]

xinput ids are not guaranteed to be stable between reboots (or hotplugs),
so add a "Evdev physical" property containing the output of the
EVIOCGPHYS ioctl as a stable identifier. This is needed to be able to
apply device-specific parameters at runtime (E.G. touchscreen
transformation in multi-head setups).

EVIOCGPHYS is used rather than E.G. the device node or sysfs path,
as it is (supposed to be) unique, simple to access and the remaining
information can be retrieved through /proc/bus/input/devices, which
doesn't require any special privileges.

Signed-off-by: Peter Korsgaard <peter.korsgaard at barco.com>
---
 include/evdev-properties.h |    3 +++
 src/evdev.c                |   16 ++++++++++++++--
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/include/evdev-properties.h b/include/evdev-properties.h
index 7df2876..6ab42b3 100644
--- a/include/evdev-properties.h
+++ b/include/evdev-properties.h
@@ -66,4 +66,7 @@
 /* BOOL */
 #define EVDEV_PROP_SWAP_AXES "Evdev Axes Swap"
 
+/* Physical location of input device as defined by the kernel */
+#define EVDEV_PROP_PHYSICAL "Evdev Physical"
+
 #endif
diff --git a/src/evdev.c b/src/evdev.c
index ccea90d..accc1d4 100644
--- a/src/evdev.c
+++ b/src/evdev.c
@@ -118,6 +118,7 @@ static Atom prop_calibration = 0;
 static Atom prop_swap = 0;
 static Atom prop_axis_label = 0;
 static Atom prop_btn_label = 0;
+static Atom prop_phys = 0;
 #endif
 
 /* All devices the evdev driver has allocated and knows about.
@@ -2453,6 +2454,17 @@ EvdevInitProperty(DeviceIntPtr dev)
     EvdevPtr     pEvdev = pInfo->private;
     int          rc;
     BOOL         invert[2];
+    char         phys[256];
+
+    if (ioctl(pInfo->fd, EVIOCGPHYS(sizeof(phys) - 1), phys) >= 0)
+    {
+        prop_phys = MakeAtom(EVDEV_PROP_PHYSICAL,
+                             strlen(EVDEV_PROP_PHYSICAL), TRUE);
+        rc = XIChangeDeviceProperty(dev, prop_phys, XA_STRING, 8,
+                                    PropModeReplace, strlen(phys), phys, FALSE);
+        if (rc != Success)
+            return;
+    }
 
     if (pEvdev->flags & (EVDEV_RELATIVE_EVENTS | EVDEV_ABSOLUTE_EVENTS))
     {
@@ -2561,8 +2573,8 @@ EvdevSetProperty(DeviceIntPtr dev, Atom atom, XIPropertyValuePtr val,
 
         if (!checkonly)
             pEvdev->swap_axes = *((BOOL*)val->data);
-    } else if (atom == prop_axis_label || atom == prop_btn_label)
-        return BadAccess; /* Axis/Button labels can't be changed */
+    } else if (atom == prop_axis_label || atom == prop_btn_label || atom == prop_phys)
+        return BadAccess; /* Axis/Button labels + phys can't be changed */
 
     return Success;
 }
-- 
1.7.0