GUAC-1389: Document file descriptor passing functions.

src/guacd/move-fd.h

@@ -26,16 +26,35 @@
 #include "config.h"
 
 /**
- * Sends the given file descriptor along the given socket. The file descriptor
+ * Sends the given file descriptor along the given socket, allowing the
- * must have been sent via guacd_recv_fd. Returns non-zero on success, zero on
+ * receiving process to use that file descriptor normally. Returns non-zero on
- * error. If an error does occur, errno will be set appropriately.
+ * success, zero on error, just as a normal call to sendmsg() would. If an
+ * error does occur, errno will be set appropriately.
+ *
+ * @param sock
+ *     The file descriptor of an open UNIX domain socket along which the file
+ *     descriptor specified by fd should be sent.
+ *
+ * @param fd
+ *     The file descriptor to send along the given UNIX domain socket.
+ *
+ * @return
+ *     Non-zero if the send operation succeeded, zero on error.
  */
 int guacd_send_fd(int sock, int fd);
 
 /**
  * Waits for a file descriptor on the given socket, returning the received file
- * descriptor. If an error occurs, -1 is returned, and errno will be set
+ * descriptor. The file descriptor must have been sent via guacd_send_fd. If an
- * appropriately.
+ * error occurs, -1 is returned, and errno will be set appropriately.
+ *
+ * @param sock
+ *     The file descriptor of an open UNIX domain socket along which the file
+ *     descriptor will be sent (by guacd_send_fd()).
+ *
+ * @return
+ *     The received file descriptor, or -1 if an error occurs preventing
+ *     receipt of the file descriptor.
  */
 int guacd_recv_fd(int sock);