#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h> 
#include <fcntl.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>

/*
 * An implementation of copy ("cp") that uses memory maps.  Various
 * error checking has been removed to promote readability
 */

// Where we want the source file's memory map to live in virtual memory
// The destination file resides immediately after the source file
#define MAP_LOCATION 0x6100

int main (int argc, char *argv[]) {
 int fdin, fdout;
 char *src, *dst;
 struct stat statbuf;
 off_t fileSize = 0;

 if (argc != 3) {
   printf ("usage: a.out <fromfile> <tofile>\n");
   exit(0);
 }

 /* open the input file */
 if ((fdin = open (argv[1], O_RDONLY)) < 0) {
   printf ("can't open %s for reading\n", argv[1]);
   exit(0);
 }

 /* open/create the output file */
 if ((fdout = open (argv[2], O_RDWR | O_CREAT | O_TRUNC, 0600)) < 0) {
   printf ("can't create %s for writing\n", argv[2]);
   exit(0);
 }
 
 /* find size of input file */
 fstat (fdin,&statbuf) ;
 fileSize = statbuf.st_size;
 
 /* go to the location corresponding to the last byte */
 if (lseek (fdout, fileSize - 1, SEEK_SET) == -1) {
   printf ("lseek error\n");
   exit(0);
 }
 
 /* write a dummy byte at the last location */
 write (fdout, "", 1);
 
 /* 
  * memory map the input file.  Only the first two arguments are
  * interesting: 1) the location and 2) the size of the memory map 
  * in virtual memory space. Note that the location is only a "hint";
  * the OS can choose to return a different virtual memory address.
  * This is illustrated by the printf command below.
 */

 src = mmap ((void*) MAP_LOCATION, fileSize, 
	     PROT_READ, MAP_SHARED, fdin, 0);

 /* memory map the output file after the input file */
 dst = mmap ((void*) MAP_LOCATION + fileSize , fileSize , 
	     PROT_READ | PROT_WRITE, MAP_SHARED, fdout, 0);


 printf("Mapped src: 0x%x  and dst: 0x%x\n",src,dst);

 /* Copy the input file to the output file */
 memcpy (dst, src, fileSize);

 // we should probably unmap memory and close the files
} /* main */