cdev: handle fast close/re-open that failed with EAGAIN

This happens with supervision tree restarts and only affects GPIOs that
are listening on interrupts.

Author: fhunleth

c_src/hal_cdev_gpio.c

@@ -231,10 +231,22 @@ int hal_open_gpio(struct gpio_pin *pin,
     int value = pin->config.is_output ? pin->config.initial_value : -1;
 
     pin->fd = request_line_v2(gpiochip_fd, pin->offset, flags, value);
+    if (pin->fd < 0) {
+        if (pin->fd == -EBUSY) {
+            // Handle supervision tree restart or any quick close/open restart
+            // where the closed file descriptor hasn't been fully released by
+            // the call to poll(3) in the interrupt thread.
+            usleep(1000);
+            pin->fd = request_line_v2(gpiochip_fd, pin->offset, flags, value);
+        }
+        if (pin->fd < 0) {
+            error("request_line_v2 failed for %s:%d, errno=%d", pin->gpiochip, pin->offset, -pin->fd);
+            close(gpiochip_fd);
+            return pin->fd;
+        }
+    }
     close(gpiochip_fd);
     debug("requesting pin %s:%d -> %d", pin->gpiochip, pin->offset, pin->fd);
-    if (pin->fd < 0)
-        return pin->fd;
 
     // Only call hal_apply_interrupts if there's a trigger
     if (pin->config.trigger != TRIGGER_NONE) {