Glib: Adding watch in the glib event poll

[Jacques Pelletier <jpelletier ieee org>]

Hi,

I want to do a customized input routine for specialized hardware plugged into 
a parallel port. I don't have any device driver yet for this hardware.

I have to poll bits; in my case, if the BUSY bit = 0, there's a character 
available on the data lines.

I made my own version of add watch routines by copying the giounix.c code in 
glib and modifiying to my needs.

Here are my questions:

In giounix.c there is this:

GSourceFuncs g_io_watch_funcs = {
  g_io_unix_prepare,
  g_io_unix_check,
  g_io_unix_dispatch,
  g_io_unix_finalize
};

Do I need to modify the g_io_unix_check routine for my needs also?
static gboolean 
g_io_unix_check (GSource  *source)
{
  GIOUnixWatch *watch = (GIOUnixWatch *)source;
  GIOCondition buffer_condition = g_io_channel_get_buffer_condition 
(watch->channel);
  GIOCondition poll_condition = watch->pollfd.revents;

  return ((poll_condition | buffer_condition) & watch->condition);
}

If I use it as is, it doesn't call my read_function.
What is it supposed to check? While it's self documented, I don't get the 
higher picture. 

--
JP