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/*
* Copyright (C) 2016 Etienne Champetier <champetier.etienne@gmail.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*/
#define _GNU_SOURCE
#include <errno.h>
#include <linux/random.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/syscall.h>
#include <unistd.h>
#define ERROR_EXIT(fmt, ...) do { \
fprintf(stderr, fmt, ## __VA_ARGS__); \
return EXIT_FAILURE; \
} while (0)
static int usage(char *name)
{
fprintf(stderr, "Usage: %s <nb>\n", name);
fprintf(stderr, " => return <nb> bytes from getrandom()\n");
return EXIT_FAILURE;
}
int main(int argc, char *argv[])
{
if (argc != 2)
return usage(argv[0]);
if (isatty(STDOUT_FILENO))
ERROR_EXIT("Not outputting random to a tty\n");
int nbtot = atoi(argv[1]);
if (nbtot < 1)
ERROR_EXIT("Invalid <nb> param (must be > 0)\n");
char buf[256];
int len = sizeof(buf);
while (nbtot > 0) {
if (nbtot <= sizeof(buf))
len = nbtot;
if (syscall(SYS_getrandom, buf, len, 0) == -1)
ERROR_EXIT("getrandom() failed: %m\n");
if (write(STDOUT_FILENO, buf, len) != len)
ERROR_EXIT("write() failed: %m\n");
nbtot -= sizeof(buf);
}
return 0;
}
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