Added waits for UDEV rules (copy of @philfifi's pull)

CONTRIBUTING.rst

@@ -17,3 +17,4 @@ Contributors
 * Simon Rowe (@srowe)
 * Steven P. Goldsmith (@sgjava)
 * Adrian Cuzman (@adriancuzman)
+* Mathieu Pasquet (@winterscar)

OPi/sysfs.py

@@ -6,29 +6,46 @@
 from OPi.constants import HIGH, LOW, IN, OUT, \
     NONE, RISING, FALLING, BOTH
 
+import os
+import time
+
+# Allow to wait up to 1 second for the file have the correct permissions
+WAIT_PERMISSION_TIMEOUT = 1.
+
+
+def await_permissions(path):
+    start_time = time.time()
+    while (not os.access(path, os.W_OK) and
+            time.time() - start_time < WAIT_PERMISSION_TIMEOUT):
+        time.sleep(0.1)
+
 
 @contextmanager
 def value_descriptor(pin, mode="r"):
     path = "/sys/class/gpio/gpio{0}/value".format(pin)
+    await_permissions(path)
     with open(path, mode) as fp:
         yield fp
 
 
 def export(pin):
     path = "/sys/class/gpio/export"
+    await_permissions(path)
     with open(path, "w") as fp:
         fp.write(str(pin))
 
 
 def unexport(pin):
     path = "/sys/class/gpio/unexport"
+    await_permissions(path)
     with open(path, "w") as fp:
         fp.write(str(pin))
 
 
 def direction(pin, dir):
     assert dir in [IN, OUT]
     path = "/sys/class/gpio/gpio{0}/direction".format(pin)
+    await_permissions(path)
     with open(path, "w") as fp:
         if dir == IN:
             fp.write("in")
@@ -54,6 +71,7 @@ def output(pin, value):
 def edge(pin, trigger):
     assert trigger in [NONE, RISING, FALLING, BOTH]
     path = "/sys/class/gpio/gpio{0}/edge".format(pin)
+    await_permissions(path)
     opts = {
         NONE: "none",
         RISING: "rising",

doc/install.rst

@@ -9,3 +9,26 @@ Install the latest version of the library directly from
 `PyPI <https://pypi.python.org/pypi?:action=display&name=OPi.GPIO>`_::
 
   $ sudo pip install --upgrade OPi.GPIO
+
+Non Root Access
+---------------
+If you want to be able to use the library as a non root user, you will need to setup a `UDEV` rule to grant you permissions first. 
+This can be accomplished as follows: 
+
+``$ sudo usermod -aG gpio <current_user>``
+
+``$ sudo nano /etc/udev/rules.d/99-gpio.rules``
+
+That should add your user to the GPIO group, create a new ``UDEV`` rule, and open it in the Nano text editor. 
+
+Enter the following into Nano
+
+
+   SUBSYSTEM=="gpio", KERNEL=="gpiochip*", ACTION=="add", PROGRAM="/bin/sh -c 'chown root:gpio /sys/class/gpio/export /sys/class/gpio/unexport ; chmod 220 /sys/class/gpio/export /sys/class/gpio/unexport'" 
+   SUBSYSTEM=="gpio", KERNEL=="gpio*", ACTION=="add", PROGRAM="/bin/sh -c 'chown root:gpio /sys%p/active_low /sys%p/direction /sys%p/edge /sys%p/value ; chmod 660 /sys%p/active_low /sys%p/direction /sys%p/edge /sys%p/value'"
+
+
+
+press ``ctrl-x``, ``Y``, and ``ENTER`` to save and close the file. 
+
+Finally, reboot and you should be ready to use ``OPi.GPIO`` as a non root user. 

tests/test_sysfs.py

@@ -7,11 +7,29 @@
 Tests for the :py:mod:`OPi.sysfs` module.
 """
 import pytest
+import time
+import threading
+import os
 
-from OPi.sysfs import export, unexport, direction, input, output, edge
+from OPi.sysfs import export, unexport, direction, input, output,\
+    edge, await_permissions, WAIT_PERMISSION_TIMEOUT
 from OPi.constants import IN, OUT, LOW, HIGH, NONE, RISING, FALLING, BOTH
 
 
+@pytest.mark.parametrize("test_input,expected", [
+    (0.1, True),
+    (1.5, False),
+])
+def test_await_permissions(fs, test_input, expected):
+    path = "/sys/class/gpio/test"
+    fs.CreateFile(path)
+    os.chmod(path, 0o444)  # revoke write permissions to the file
+    start_time = time.time()
+    threading.Timer(test_input, lambda: os.chmod(path, 0o666)).start()
+    await_permissions(path)
+    assert (time.time() - start_time < WAIT_PERMISSION_TIMEOUT) == expected
+
+
 def test_export(fs):
     fs.CreateFile("/sys/class/gpio/export")
     export(19)