/*
 * problem 9.5, pg 812 :
 * Use mmap to copy an arbitrary sized file to stdout.
 * The name of the file should be passed as a command line argument.
 *
 * See "man fstat", "man open", "man write".
 *
 *  $ gcc 9p5.c -o 9p5
 *  $ ./9p5 9p5.c
 *  ... this file ...
 *
 */

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

/*
  The mmap call looks like this :

  void *mmap(void *start,       // requested start address
  	     size_t length,     //
	     int prot,          // protections, e.g. PROT_WRITE | PROT_READ
	     int flags,         // other options, e.g. MAP_PRIVATE
	     int fd,            // file descriptor
	     off_t offset,      //
	     )

  See man (3) pages for fstat, open, write.
  See e.g. http://en.wikipedia.org/wiki/Standard_streams
  for standard streams; (0,2,1) are (stdin, stdout, stderr)

*/

// Use mmap to copy a file to stdout
void mmapcopy(int fd, int size){
  char* buffer;  // pointer to memory-mapped virtual memory area
  buffer = mmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
  write(1, buffer, size);
  return;
}

int main(int argc, char* argv[]){
  int fd;                       // file descriptor
  struct stat file_status;

  // Confirm correct number of arguments. 
  if (argc != 2){
    printf("Usage: %s <filename>\n", argv[0]);
    exit(0);
  }

  // Open file, get size, do copy.
  fd = open(argv[1], O_RDONLY, 0);   // read-only
  fstat(fd, &file_status);
  mmapcopy(fd, file_status.st_size);
  exit(0);
}