1/* Implementation of getentropy based on getrandom.
2 Copyright (C) 2016-2024 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19#include <sys/random.h>
20#include <assert.h>
21#include <errno.h>
22#include <unistd.h>
23#include <hurd.h>
24
25/* Write LENGTH bytes of randomness starting at BUFFER. Return 0 on
26 success and -1 on failure. */
27int
28getentropy (void *buffer, size_t length)
29{
30 /* The interface is documented to return EIO for buffer lengths
31 longer than 256 bytes. */
32 if (length > 256)
33 return __hurd_fail (EIO);
34
35 /* Try to fill the buffer completely. Even with the 256 byte limit
36 above, we might still receive an EINTR error (when blocking
37 during boot). */
38 void *end = buffer + length;
39 while (buffer < end)
40 {
41 /* NB: No cancellation point. */
42 ssize_t bytes = __getrandom (buffer, end - buffer, 0);
43 if (bytes < 0)
44 {
45 if (errno == EINTR)
46 /* Try again if interrupted by a signal. */
47 continue;
48 else
49 return -1;
50 }
51 if (bytes == 0)
52 /* No more bytes available. This should not happen under
53 normal circumstances. */
54 return __hurd_fail (EIO);
55 /* Try again in case of a short read. */
56 buffer += bytes;
57 }
58 return 0;
59}
60

source code of glibc/sysdeps/mach/hurd/getentropy.c