paging.h

// paging.h
// Enables paging management for the kernel (x86 arch).
// Based on JamesM's kernel tutorial.

#ifndef PAGING_H
#define PAGING_H

#include "common.h"
#include "isr.h"

typedef struct page
{
    u32int present  : 1;    // Page present in memory.
    u32int rw       : 1;    // Read-only if clear, readwrite if set.
    u32int user     : 1;    // Supervisor level only if clear.
    u32int accessed : 1;    // Has the page been accessed since last refresh?
    u32int dirty    : 1;    // Has the page been written to since last refresh?
    u32int unused   : 7;    // Amalgamation of unused and reserved bits.
    u32int frame    : 20;   // Frame address (shifted right 12 bits).
} page_t;

typedef struct page_table
{
    page_t pages[1024];
} page_table_t;

typedef struct page_directory
{
    page_table_t *tables[1024];      // Array of pointers to pagetables.
    u32int tablesPhysical[1024];     // Array of pointers to physical location.
    u32int physicalAddr;             // The physical address ot tablesPhysical.
} page_directory_t;

// Sets up the environment, page directoruies etc and enables paging.
void initialise_paging(void);

// Causes the specified page directory to be loaded into the CR3 register.
void switch_page_directory(page_directory_t *new_pd);

/**
    Retrieves a pointer tot he page required.
    If make == 1, if the page table in which this page should
    reside isn't created, create it!
**/
page_t *get_page(u32int address, int make, page_directory_t *dir);

// Handler for page faults.
void page_fault(registers_t regs);

void alloc_frame(page_t *page, int is_kernel, int is_writtable);

void free_frame(page_t *page);

#endif