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/* Implementation of getentropy based on the getrandom system call.
Copyright (C) 2016-2020 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library 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
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <sys/random.h>
#include <assert.h>
#include <errno.h>
#include <unistd.h>
/* Write LENGTH bytes of randomness starting at BUFFER. Return 0 on
success and -1 on failure. */
int
getentropy (void *buffer, size_t length)
{
/* The interface is documented to return EIO for buffer lengths
longer than 256 bytes. */
if (length > 256)
{
__set_errno (EIO);
return -1;
}
/* Try to fill the buffer completely. Even with the 256 byte limit
above, we might still receive an EINTR error (when blocking
during boot). */
void *end = buffer + length;
while (buffer < end)
{
/* NB: No cancellation point. */
ssize_t bytes = INLINE_SYSCALL_CALL (getrandom, buffer, end - buffer, 0);
if (bytes < 0)
{
if (errno == EINTR)
/* Try again if interrupted by a signal. */
continue;
else
return -1;
}
if (bytes == 0)
{
/* No more bytes available. This should not happen under
normal circumstances. */
__set_errno (EIO);
return -1;
}
/* Try again in case of a short read. */
buffer += bytes;
}
return 0;
}
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