Function get_hid_report_descriptor

lib/hidapi/linux/hid.c:356–382

* Retrieves the hidraw report descriptor from a file. * When using this form, /device/report_descriptor, elevated priviledges are not required. */

 * When using this form, <sysfs_path>/device/report_descriptor, elevated priviledges are not required.
 */
static int get_hid_report_descriptor(const char *rpt_path, struct hidraw_report_descriptor *rpt_desc)
{
	int rpt_handle;
	ssize_t res;

	rpt_handle = open(rpt_path, O_RDONLY | O_CLOEXEC);
	if (rpt_handle < 0) {
		register_global_error_format("open failed (%s): %s", rpt_path, strerror(errno));
		return -1;
	}

	/*
	 * Read in the Report Descriptor
	 * The sysfs file has a maximum size of 4096 (which is the same as HID_MAX_DESCRIPTOR_SIZE) so we should always
	 * be ok when reading the descriptor.
	 * In practice if the HID descriptor is any larger I suspect many other things will break.
	 */
	memset(rpt_desc, 0x0, sizeof(*rpt_desc));
	res = read(rpt_handle, rpt_desc->value, HID_MAX_DESCRIPTOR_SIZE);
	if (res < 0) {
		register_global_error_format("read failed (%s): %s", rpt_path, strerror(errno));
	}
	rpt_desc->size = (__u32) res;

	close(rpt_handle);
	return (int) res;
}

/* return size of the descriptor, or -1 on failure */
static int get_hid_report_descriptor_from_sysfs(const char *sysfs_path, struct hidraw_report_descriptor *rpt_desc)