agents: sysfsgpio: Fix remote GPIO export

Fixes the exception ValueError("can't have unbuffered text I/O") when
opening the export sysfs file to export a GPIO using the remote agent.
The file should be open in binary mode and the export string encoded to
match.

Signed-off-by: Joshua Watt <[email protected]>

Author: JPEWdev

labgrid/util/agents/sysfsgpio.py

@@ -9,17 +9,15 @@
 
 class GpioDigitalOutput:
     _gpio_sysfs_path_prefix = '/sys/class/gpio'
-    _buffered_file_access = False
 
     @staticmethod
     def _assert_gpio_line_is_exported(index):
         gpio_sysfs_path = os.path.join(GpioDigitalOutput._gpio_sysfs_path_prefix,
                                        'gpio{0}'.format(index))
         if not os.path.exists(gpio_sysfs_path):
             export_sysfs_path = os.path.join(GpioDigitalOutput._gpio_sysfs_path_prefix, 'export')
-            with open(export_sysfs_path, mode='r+',
-                      buffering=GpioDigitalOutput._buffered_file_access) as export:
-                export.write(str(index))
+            with open(export_sysfs_path, mode='wb') as export:
+                export.write(str(index).encode('utf-8'))
         if not os.path.exists(gpio_sysfs_path):
             raise ValueError("Device not found")