Системный вызов sendfile()

#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sys/sendfile.h>
#include <sys/stat.h>
 
int main (int argc, char** argv)
{
  int src;               /* file descriptor for source file */
  int dest;              /* file descriptor for destination file */
  struct stat stat_buf;  /* hold information about input file */
  off_t offset = 0;      /* byte offset used by sendfile */
  int rc;                /* return code from sendfile */
 
  /* check for two command line arguments */
  if (argc != 3) {
    fprintf(stderr, "usage: %s <file> <copy>\n", argv[0]);
    exit(1);
  }
 
  /* check that source file exists and can be opened */
  src = open(argv[1], O_RDONLY);
  if (src == -1) {
    fprintf(stderr, "unable to open '%s': %s\n", argv[1], strerror(errno));
    exit(1);
  }
 
 /* get size and permissions of the source file */
  fstat(src, &stat_buf);
 
  
 
 /* open destination file */
  dest = open(argv[2], O_RDWR | O_CREAT);
  if (dest == -1) {
    fprintf(stderr, "unable to open '%s': %s\n", argv[2], strerror(errno));
    exit(1);
  }
 
  printf("-=src=%d=-\n", src);
  printf("-=dest=%d=-\n", dest);
  printf("-=sixe=%d=-\n", stat_buf.st_size);
  
 /* copy file using sendfile */
 rc = sendfile (dest, src, &offset, stat_buf.st_size);
 if (rc == -1) {
    fprintf(stderr, "error from sendfile: %s\n", strerror(errno));
    exit(1);
 }
 if (rc != stat_buf.st_size) {
   fprintf(stderr, "incomplete transfer from sendfile: %d of %d bytes\n",
           rc,
           (int)stat_buf.st_size);
   exit(1);
 }
 
 /* clean up and exit */
 close(dest);
 close(src);
 
 return 0;
}