/* mapcat: mmap() a file and copy it to stdout.
   Useful for reading special files that can be mmapped but not read.
   Written by Phil Endecott, 2008.
   I place this code in the public domain; do what you like with it.
*/

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


int main(int argc, char* argv[])
{
  if (argc!=3) {
    fputs("Usage: mapcat <filname> <length>\n", stderr);
    exit(1);
  }

  const char* fn = argv[1];

  char* endptr;
  size_t length = strtoul(argv[2],&endptr,0);
  if (*endptr) {
    fprintf(stderr,"Failed to parse length '%s' at character '%c'\n",argv[2],*endptr);
    exit(1);
  }

  int fd = open(fn,O_RDONLY);
  if (fd==-1) {
    perror("open()");
    exit(1);
  }

  void* addr = mmap(NULL, length, PROT_READ, MAP_SHARED, fd, 0);
  if (addr==MAP_FAILED) {
    perror("mmap()");
    exit(1);
  }

  void* buf = malloc(length);
  if (!buf) {
    perror("malloc()");
    exit(1);
  }
  memcpy(buf,addr,length);

  int bytes_left=length;
  void* p = buf;
  while (bytes_left) {
    int b = write(1,p,bytes_left);
    if (b==0) {
      perror("write()");
      exit(1);
    }
    p += b;
    bytes_left -= b;
  }
}