mycp.c

gistfile1.txt

#include <stdio.h>
#include <stdlib.h>
#include <sys/sendfile.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

#define _GNU_SOURCE
#include <fcntl.h>

static int openfile(char *path, int flags, mode_t mode) {
  int fd = open(path, flags, mode);
  if (fd == -1) {
    perror("open failed");
    exit(1);
  }
  return fd;
}

static off_t filesize(int fd) {
  struct stat st;
  if (fstat(fd, &st) == -1) {
    perror("fstat failed");
    exit(1);
  }
  return st.st_size;
}

int main(int argc, char **argv) {
  if (argc != 3) {
    fprintf(stderr, "Usage: %s SOURCE DEST\n", argv[0]);
    return 1;
  }

  int in = openfile(argv[1], O_RDONLY, 0);
  int out = openfile(argv[2], O_WRONLY | O_CREAT, 0644);

  off_t len = filesize(in);

  if (sendfile(out, in, NULL, len) == -1) {
    perror("sendfile failed");
    exit(1);
  }
  return 0;
}