BUG=chrome-os-partner:28870
TEST=Manually on Beaglebone
  1. Check help string
     $ python polld.py -h
     $ python poll_client.py -h

  2. Start polld
     $ python polld.py -d

  3. Check gpio7 and gpio8 are not exported yet
     $ ls -d /sys/class/gpio/gpio[78] # should fail

  4. Run multiple clients to watch gpio7 and gpio8
     $ python poll_client.py -r 100 gpio_falling:7
     $ python poll_client.py -r 100 gpio_falling:7
     $ python poll_client.py -r 100 gpio_rising:8
     They should all blocks

  5. Check /sys/class/gpio/gpio7/edge == falling
     and gpio8/edge == rising

  6. Connect voltage 3.3V to GPIO7, then change to GND.
     The two clients waiting for GPIO7 should be notified.

  8. Stop polld.py by Ctrl+C or SIGTERM.
     Check gpio7 and gpio8 under sysfs are unexported again.

Change-Id: Icf5532060a8212c15738f4881ecc1ba2be9dbea6
Reviewed-on: https://chromium-review.googlesource.com/204823


Reviewed-by: Dean Liao <deanliao@chromium.org>
Commit-Queue: Justin Chuang <jchuang@chromium.org>
Tested-by: Justin Chuang <jchuang@chromium.org>