prober: Add ability to get string descriptors.

Right now we can only use libusb to get this info.

src/xrt/include/xrt/xrt_prober.h

@@ -94,6 +94,16 @@ enum xrt_bus_type
 	XRT_BUS_TYPE_BLUETOOTH,
 };
 
+/*!
+ * String descriptor types
+ */
+enum xrt_prober_string
+{
+	XRT_PROBER_STRING_MANUFACTURER,
+	XRT_PROBER_STRING_PRODUCT,
+	XRT_PROBER_STRING_SERIAL_NUMBER,
+};
+
 /*!
  * A probed device, may or may not be opened.
  *
@@ -137,6 +147,11 @@ struct xrt_prober
 	int (*list_video_devices)(struct xrt_prober *xp,
 	                          xrt_prober_list_video_cb cb,
 	                          void *ptr);
+	int (*get_string_descriptor)(struct xrt_prober *xp,
+	                             struct xrt_prober_device *xpdev,
+	                             enum xrt_prober_string which_string,
+	                             unsigned char *buffer,
+	                             int length);
 	void (*destroy)(struct xrt_prober **xp_ptr);
 };
 
@@ -189,6 +204,22 @@ xrt_prober_open_hid_interface(struct xrt_prober *xp,
 	return xp->open_hid_interface(xp, xpdev, interface, out_hid_dev);
 }
 
+/*!
+ * Helper function for @ref xrt_prober::get_string_descriptor.
+ *
+ * @ingroup xrt_iface
+ */
+XRT_MAYBE_UNUSED static inline int
+xrt_prober_get_string_descriptor(struct xrt_prober *xp,
+                                 struct xrt_prober_device *xpdev,
+                                 enum xrt_prober_string which_string,
+                                 unsigned char *buffer,
+                                 int length)
+{
+	return xp->get_string_descriptor(xp, xpdev, which_string, buffer,
+	                                 length);
+}
+
 /*!
  * Helper function for @ref xrt_prober::list_video_devices.
  *

src/xrt/state_trackers/prober/p_libusb.c

@@ -94,3 +94,50 @@ p_libusb_probe(struct prober *p)
 
 	return 0;
 }
+
+int
+p_libusb_get_string_descriptor(struct prober *p,
+                               struct prober_device *pdev,
+                               enum xrt_prober_string which_string,
+                               unsigned char *buffer,
+                               int length)
+{
+
+	struct libusb_device_descriptor desc;
+
+	libusb_device *usb_dev = pdev->usb.dev;
+	int result = libusb_get_device_descriptor(usb_dev, &desc);
+	if (result < 0) {
+		P_ERROR(p, "libusb_get_device_descriptor failed!");
+		return result;
+	}
+	uint8_t which = 0;
+	switch (which_string) {
+	case XRT_PROBER_STRING_MANUFACTURER: which = desc.iManufacturer; break;
+	case XRT_PROBER_STRING_PRODUCT: which = desc.iProduct; break;
+	case XRT_PROBER_STRING_SERIAL_NUMBER: which = desc.iSerialNumber; break;
+	default: break;
+	}
+	P_SPEW(p,
+	       "libusb\n"
+	       "\t\tptr:        %p\n"
+	       "\t\trequested string index:  %i",
+	       (void *)pdev, which);
+	if (which == 0) {
+		// Not available?
+		return 0;
+	}
+	libusb_device_handle *dev_handle = NULL;
+	result = libusb_open(usb_dev, &dev_handle);
+	if (result < 0) {
+		P_ERROR(p, "libusb_open failed!");
+		return result;
+	}
+	int string_length = libusb_get_string_descriptor_ascii(
+	    dev_handle, which, buffer, length);
+	if (string_length < 0) {
+		P_ERROR(p, "libusb_get_string_descriptor_ascii failed!");
+	}
+	libusb_close(dev_handle);
+	return string_length;
+}

src/xrt/state_trackers/prober/p_prober.c

@@ -57,6 +57,12 @@ static int
 list_video_devices(struct xrt_prober* xp,
                    xrt_prober_list_video_cb cb,
                    void* ptr);
+static int
+get_string_descriptor(struct xrt_prober* xp,
+                      struct xrt_prober_device* xpdev,
+                      enum xrt_prober_string which_string,
+                      unsigned char* buffer,
+                      int length);
 
 static void
 destroy(struct xrt_prober** xp);
@@ -229,6 +235,7 @@ initialize(struct prober* p, struct xrt_prober_entry_lists* lists)
 	p->base.select = select_device;
 	p->base.open_hid_interface = open_hid_interface;
 	p->base.list_video_devices = list_video_devices;
+	p->base.get_string_descriptor = get_string_descriptor;
 	p->base.destroy = destroy;
 	p->lists = lists;
 	p->print_spew = debug_get_bool_option_prober_spew();
@@ -582,6 +589,29 @@ list_video_devices(struct xrt_prober* xp,
 	return 0;
 }
 
+static int
+get_string_descriptor(struct xrt_prober* xp,
+                      struct xrt_prober_device* xpdev,
+                      enum xrt_prober_string which_string,
+                      unsigned char* buffer,
+                      int length)
+{
+	struct prober* p = (struct prober*)xp;
+	struct prober_device* pdev = (struct prober_device*)xpdev;
+	int ret;
+#ifdef XRT_HAVE_LIBUSB
+	if (pdev->usb.dev != NULL) {
+		ret = p_libusb_get_string_descriptor(p, pdev, which_string,
+		                                     buffer, length);
+		if (ret >= 0) {
+			return ret;
+		}
+	}
+#endif
+	//! @todo add more backends
+	//! @todo make this unicode (utf-16)? utf-8 would be better...
+	return 0;
+}
 static void
 destroy(struct xrt_prober** xp)
 {

src/xrt/state_trackers/prober/p_prober.h

@@ -201,6 +201,13 @@ p_libusb_teardown(struct prober* p);
 
 int
 p_libusb_probe(struct prober* p);
+
+int
+p_libusb_get_string_descriptor(struct prober* p,
+                               struct prober_device* pdev,
+                               enum xrt_prober_string which_string,
+                               unsigned char* buffer,
+                               int length);
 #endif
 
 #ifdef XRT_HAVE_LIBUVC