/******************************
* filemap.c 
* provides a memory mapped file to caller
*
*******************************/
#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <errno.h>

/* returns the size in bytes of the file */

size_t filesize(int fd)
{
	struct stat st;
	if(fstat(fd,&st)==(-1))
	{
		perror("Cannot stat input file");
		exit(EXIT_FAILURE);
	}
	return st.st_size;
}
/***********************
* mapfile maps a file into memory
* arg:
*    filename - name of the file to map
*    fd - files descriptor - mapfile sets this to an open fd
*    filelen - length of file - mapfile sets this to len of file in bytes 
* returns:
*    pointer to file (byte 0 of file) in memory
*
*    any changes made to file in memory are not reflected in the physical file.
***************************/
caddr_t *mapfile(const char *filename, int *fd, size_t *filelen)
{
    int filedesc=0; 
    size_t len=0;
    caddr_t *mapptr;
	if( (filedesc=open(filename,O_RDONLY))<0)
	{
		perror("Input file open failure");
		exit(EXIT_FAILURE);
	}
	*fd=filedesc;
	len=filesize(filedesc);	
	*filelen=len;
	mapptr=(caddr_t *)mmap(NULL, 
	                       len,
	                       PROT_READ|PROT_WRITE,
	                       MAP_PRIVATE,  
	                       filedesc, 
	                       0);
	if(mapptr==MAP_FAILED)
	{
		 perror("Memory mapping of file failed.");
		 exit(EXIT_FAILURE);
	}    
	return mapptr;
}

/* close files and release memory */
void mapcleanup(caddr_t *ptr, int fd, size_t filelen )
{
	if(munmap(ptr,filelen)==(-1))
	{
		 perror("Error releasing memory");
		 exit(EXIT_FAILURE);
	}
	while(close(fd)==(-1))
	{
		if(errno=EINTR)
		{
			continue;
		}
		else
		{
			perror("File I/O Error");
			exit(EXIT_FAILURE);
		}
	}		
}