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>Pardevices and parport_drivers</H1
><P
> When a parallel port device driver (such as
<TT
CLASS="LITERAL"
>lp</TT
>) initialises it tells the sharing layer
about itself using <TT
CLASS="FUNCTION"
>parport_register_driver</TT
>.
The information is put into a <SPAN
CLASS="STRUCTNAME"
>struct
parport_driver</SPAN
>, which is put into a linked list. The
information in a <SPAN
CLASS="STRUCTNAME"
>struct parport_driver</SPAN
>
really just amounts to some function pointers to callbacks in the
parallel port device driver.
</P
><P
> During its initialisation, a low-level port driver tells the
sharing layer about all the ports that it has found (using
<TT
CLASS="FUNCTION"
>parport_register_port</TT
>), and the sharing layer
creates a <SPAN
CLASS="STRUCTNAME"
>struct parport</SPAN
> for each of
them. Each <SPAN
CLASS="STRUCTNAME"
>struct parport</SPAN
> contains
(among other things) a pointer to a <SPAN
CLASS="STRUCTNAME"
>struct
parport_operations</SPAN
>, which is a list of function
pointers for the various operations that can be performed on a
port. You can think of a <SPAN
CLASS="STRUCTNAME"
>struct parport</SPAN
>
as a parallel port <SPAN
CLASS="QUOTE"
>"object"</SPAN
>, if
<SPAN
CLASS="QUOTE"
>"object-orientated"</SPAN
> programming is your thing. The
<SPAN
CLASS="STRUCTNAME"
>parport</SPAN
> structures are chained in a
linked list, whose head is <TT
CLASS="VARNAME"
>portlist</TT
> (in
<TT
CLASS="FILENAME"
>drivers/parport/share.c</TT
>).
</P
><P
> Once the port has been registered, the low-level port driver
announces it. The <TT
CLASS="FUNCTION"
>parport_announce_port</TT
>
function walks down the list of parallel port device drivers
(<SPAN
CLASS="STRUCTNAME"
>struct parport_driver</SPAN
>s) calling the
<TT
CLASS="FUNCTION"
>attach</TT
> function of each (which may block).
</P
><P
> Similarly, a low-level port driver can undo the effect of
registering a port with the
<TT
CLASS="FUNCTION"
>parport_unregister_port</TT
> function, and device
drivers are notified using the <TT
CLASS="FUNCTION"
>detach</TT
>
callback (which may not block).
</P
><P
> Device drivers can undo the effect of registering themselves with
the <TT
CLASS="FUNCTION"
>parport_unregister_driver</TT
>
function.
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