//-------------------------------------------------------------------
//	pgdir.c
//
//	This module implements a 'visualization' of the 4GB virtual
//	address space under Linux, based on page-directory entries.
//	The data-granularity depicted is 4MB.  Frames which are not
//	presently 'mapped' are shown by '-', while frames which are
//	mapped are marked by a character ('3' or '7') based on bits
//	from the page-directory entry. 
//
//	     Usage: Compile and install the module object-file, 
//	     then execute the shell-command: $ cat /proc/pgdir
//
//	NOTE: Written and tested using Linux kernel version 2.4.20.
//
//	programmer: ALLAN CRUSE
//	written on: 16 FEB 2003
//-------------------------------------------------------------------

#define	__KERNEL__
#define	  MODULE  

#include <linux/module.h>	// for init_module() 
#include <linux/proc_fs.h>	// for create_proc_read_entry() 
#include <asm/io.h>		// for phys_to_virt()

#define	SUCCESS	0

static char modname[] = "pgdir";

static int my_proc_read( char *buf, char **start, off_t off,
				int count, int *eof, void *data );



int init_module( void )
{
	printk( "<1>\nInstalling \'%s\' module\n", modname );

	create_proc_read_entry( modname, 0, NULL, my_proc_read, NULL );
	return	SUCCESS;
}



void cleanup_module( void )
{
	remove_proc_entry( modname, NULL );

	printk( "<1>Removing \'%s\' module\n", modname );
}


MODULE_LICENSE("GPL"); 



static int my_proc_read( char *buf, char **start, off_t off,
				int count, int *eof, void *data )
{
	unsigned long	ptdb, *pgdir;
	int		i, k, len;

	// inline assembly-language is used to access register CR3 
	asm(" movl %%cr3, %%eax \n movl %%eax, %0 " : "=m" (ptdb) );
	pgdir = (unsigned long *)phys_to_virt( ptdb );
	
	// title for the visualization
	len = 0;
	len += sprintf( buf+len, "\n\n  " );
	len += sprintf( buf+len, "A \'scientific visualization\' for the " );
	len += sprintf( buf+len, "IA-32 Virtual Address Space under Linux\n" );

	// loop through page-directory entries (from highest to lowest)
	for (i = 0; i < 1024; i++)
		{
		int		k = 1023- i;
		unsigned char	attr = (pgdir[ k ]&7) | '0';
		if ( !(attr&1) ) attr = '-';
		if ( ( i % 64 ) == 0 ) len += sprintf( buf+len, "\n   " );
		len += sprintf( buf+len, "%c", attr );
		if ( ( i % 64 ) == 63 ) 
			len += sprintf( buf+len, "  %08X", k<<22 );
	       	}	
	// display explanatory legend (plus some extra info)
	len += sprintf( buf+len, "\n\n\n   Legend:  " );
	len += sprintf( buf+len, " \'-\'=unmapped  " );
	len += sprintf( buf+len, " \'3\'=supervisor  " );
	len += sprintf( buf+len, " \'7\'=user  " );
	len += sprintf( buf+len, "         (CR3=%08X) ", ptdb );
	len += sprintf( buf+len, "\n\n" );

	*eof = 1;
	return	len;
}