regarding the structures of framebuffer driver

Hi all,

I am very new to video drivers and iam working on framebuffer drivers.
Pls help me clear my doubts.
This mail is regarding the structures of framebuffer driver

I have some doubt regarding the kernel structures I have found in the
skeletonfb.c file which model of framebuffer driver.

I am not able to understand the following parts of code :-
I am separating each section of code by " ******** ".

************************************************************************
****

/* ------------ Interfaces to hardware functions ------------ */


struct fbgen_hwswitch xxx_switch = {
    xxx_detect, xxx_encode_fix, xxx_decode_var, xxx_encode_var,
xxx_get_par,
    xxx_set_par, xxx_getcolreg, xxx_setcolreg, xxx_pan_display,
xxx_blank,
    xxx_set_disp
};

/*---------------- chipset specific functions --------------------------
*/

Followed by comment the above "fbgen_hwswitch" structure functions were
defined.
R the function pointers declared in the above "fbgen_hwswitch" structure
a sort of call back functions.
Will they be called from the user space (Application like X server)?

If so, where is the list of user space calls from which the above
functions will be called? 
R these user space calls valid whether there is a X server on top of
framebuffer driver or any other application which can directly interact?
( I heard from the NET, there will be applications like X server which
can    directly interact with framebuffer driver. )

************************************************************************
****
static struct fb_ops xxxfb_ops = {
	owner:		THIS_MODULE,
	fb_open:	xxxfb_open,    /* only if you need it to do
something */
	fb_release:	xxxfb_release, /* only if you need it to do
something */
	fb_get_fix:	fbgen_get_fix,
	fb_get_var:	fbgen_get_var,
	fb_set_var:	fbgen_set_var,
	fb_get_cmap:	fbgen_get_cmap,
	fb_set_cmap:	fbgen_set_cmap,
	fb_pan_display:	fbgen_pan_display,
	fb_ioctl:	xxxfb_ioctl,   /* optional */
};

Also, where can I find the call backs for these functions?
Where is XFree86 driver source in /usr/?.


Thanks a lot in advance,
Mukund jampala





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