/* Implementation of getentropy based on the getrandom system call.

   Copyright (C) 2016-2018 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

   <http://www.gnu.org/licenses/>.  */

#include <sys/random.h>

#include <assert.h>

#include <errno.h>

#include <unistd.h>

#ifdef __NR_getrandom

/* 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;

}

#else

int

getentropy (void *buffer, size_t length)

{

  __set_errno (ENOSYS);

  return -1;

}

#endif