GlFdHandler
GlFdHandler rd; /* The callback to call when fd is readable */
GlFdHandler wr; /* The callback to call when fd is writable */
GlFdHandler ur; /* The callback to call when fd has urgent data */
static int gl_call_fd_handler(GetLine *gl, GlFdHandler *gfh, int fd,
static int gl_call_fd_handler(GetLine *gl, GlFdHandler *gfh, int fd,