copy_file_range.c

#define _GNU_SOURCE
#include <stdlib.h>
#include <unistd.h>
#include <limits.h>
#include <stdio.h>
#include <linux/types.h>

size_t max = (size_t)LONG_MAX +1; // (size_t)LONG_MAX+1
loff_t off = 0;

#define ISUNSIGNED(a) (a >= 0 && ~a >= 0)


int main() {
  FILE *fa = fopen("a.txt", "rb");
  FILE *fb = fopen("b.txt", "wb");
  printf("sizes: size_t %p, ssize_t %p, loff_t %p, loff_t unsigned %d\n", sizeof((size_t)0), sizeof((ssize_t)0), sizeof((loff_t)0), ISUNSIGNED(off));
  printf("calling copy_file_range with len %p\n", max);
  if (copy_file_range(fileno(fa), NULL, fileno(fb), NULL, max, 0) < 0) {
          perror(NULL);
  }
}