Add some hacky PoC XLib/XInput C code to fetch slave device nodes

xdg/get-x-slave-devnodes/Makefile

@@ -0,0 +1,5 @@
+get-x-slave-devnodes: get-x-slave-devnodes.c
+	$(CC) -O2 --std=c99 -pedantic -Wall get-x-slave-devnodes.c -o get-x-slave-devnodes -lX11 -lXi
+clean:
+	rm -f get-x-slave-devnodes
+

xdg/get-x-slave-devnodes/get-x-slave-devnodes.c

@@ -0,0 +1,160 @@
+/*
+ * Loosely based on a mix of:
+ *   - xorg-xinput
+ *     https://github.com/freedesktop/xorg-xinput/blob/master/src/property.c::print_property_xi2
+ *   - xkbcat
+ *     https://github.com/anko/xkbcat
+*/
+
+#include <string.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <stdbool.h>
+
+#include <X11/extensions/XInput2.h>
+#include <X11/Xatom.h>
+
+
+char* get_property_xi2(Display* dpy, int deviceid, Atom property, const char* property_name)
+{
+    Atom act_type;
+    char* name;
+    int act_format;
+    unsigned long nitems, bytes_after;
+    unsigned char* data;
+    unsigned char* ptr;
+    int j, done = False;
+    char* ret = NULL;
+
+    name = XGetAtomName(dpy, property);
+    int interested_in_property = (strcmp(name, property_name) == 0);
+    XFree(name);
+    if (!interested_in_property)
+        return ret;
+
+    if (XIGetProperty(dpy, deviceid, property, 0, 1000, False,
+                           AnyPropertyType, &act_type, &act_format,
+                           &nitems, &bytes_after, &data) == Success)
+    {
+        ptr = data;
+        for (j = 0; j < nitems; j++)
+        {
+            switch(act_type)
+            {
+                case XA_STRING:
+                    if (act_format != 8)
+                    {
+                        //Unknown string format
+                        done = True;
+                        break;
+                    }
+
+                    int len = strlen((char*)ptr);
+                    ret = (char*)malloc(len+1);
+                    strcpy(ret, (const char*)ptr);
+
+                    j += len; /* The loop's j++ jumps over the
+                                                terminating 0 */
+                    ptr += len; /* ptr += size below jumps over
+                                            the terminating 0 */
+                    break;
+                default:
+                    // Unknown type
+                    done = True;
+                    break;
+            }
+
+            ptr += act_format/8;
+
+            if (done == True)
+                break;
+        }
+        XFree(data);
+    }
+    return ret;
+}
+
+
+void assert_xinput2(Display* disp)
+{
+    int xiOpcode;
+    { // Test for XInput 2 extension
+        int queryEvent, queryError;
+        if (! XQueryExtension(disp, "XInputExtension", &xiOpcode, &queryEvent, &queryError))
+        {
+            fprintf(stderr, "X Input extension not available\n");
+            exit(2);
+        }
+    }
+    { // Request XInput 2.0, to guard against changes in future versions
+        int major = 2, minor = 0;
+        int queryResult = XIQueryVersion(disp, &major, &minor);
+        if (queryResult == BadRequest)
+        {
+            fprintf(stderr, "Need XI 2.0 support (got %d.%d)\n", major, minor);
+            exit(3);
+        }
+        else if (queryResult != Success)
+        {
+            fprintf(stderr, "XIQueryVersion failed!\n");
+            exit(4);
+        }
+    }
+}
+
+
+void print_device_nodes(Display* disp)
+{
+	XIDeviceInfo* all_slaves;
+	XIDeviceInfo* current_slave;
+	int num_slaves;
+
+	all_slaves = XIQueryDevice(disp, XIAllDevices, &num_slaves);
+	for (int i = 0; i < num_slaves; i++)
+	{
+		current_slave = &all_slaves[i];
+
+        int nprops;
+        Atom* props;
+        props = XIListProperties(disp, current_slave->deviceid, &nprops);
+        if (!nprops)
+            printf("Device '%s' does not report any properties.\n", current_slave->name);
+
+        while(nprops--)
+        {
+            char* property = get_property_xi2(disp, current_slave->deviceid, props[nprops], "Device Node");
+            if (property != NULL)
+            {
+                printf("%s=%s\n", current_slave->name, property);
+                free(property);
+            }
+        }
+        XFree(props);
+	}
+
+	XIFreeDeviceInfo(all_slaves);
+}
+
+
+int main(int argc, char * argv[])
+{
+    char* xDisplayName = getenv("DISPLAY");
+    if (xDisplayName == NULL)
+    {
+        printf("DISPLAY environment variable not found\n");
+        exit(1);
+    }
+
+    // Connect to X display
+    Display* disp = XOpenDisplay(xDisplayName);
+    if (NULL == disp)
+    {
+        fprintf(stderr, "Cannot open X display '%s'\n", xDisplayName);
+        exit(1);
+    }
+    assert_xinput2(disp);
+
+    print_device_nodes(disp);
+    exit(0);
+}