Driver data structures

Framebuffer drivers depend heavily on four data structures, all defined in include/linux/fb.h, which is also the header you should include in your code in order to deal with framebuffer drivers:

#include <linux/fb.h> 

These structures are fb_var_screeninfo, fb_fix_screeninfo, fb_cmap, and fb_info. The first three are made available to and from the user space code. Now let's describe the purpose of each structure, their meaning, and what they are used for:

1. The kernel uses an instance of struct fb_var_screeninfo to hold variable properties of the video card. These values are those defined by the user, such as resolution depth:

struct fb_var_screeninfo { 
   __u32 xres; /* visible resolution */ 
   __u32 yres; 
 
   __u32 xres_virtual; /* virtual resolution */ 
   __u32 yres_virtual; 
 
   __u32 xoffset; /* offset from virtual to visible resolution */ 
   __u32 yoffset; 
 
   __u32 bits_per_pixel; /* # of bits needed to hold a pixel */ 
   [...] 
 
   /* Timing: All...