include/sys/random.h

/****************************************************************************
 * include/sys/random.h
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The
 * ASF licenses this file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 ****************************************************************************/

#ifndef __INCLUDE_SYS_RANDOM_H
#define __INCLUDE_SYS_RANDOM_H

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <stddef.h>

/****************************************************************************
 * Pre-processor Definitions
 ****************************************************************************/

/* Flags for getrandom(2)
 *
 * GRND_NONBLOCK  Don't block and return EAGAIN instead
 * GRND_RANDOM    Open /dev/random instead of /dev/urandom
 * GRND_INSECURE  Return non-cryptographic random bytes
 */

#define GRND_NONBLOCK   (1 << 0)
#define GRND_RANDOM     (1 << 1)
#define GRND_INSECURE   (1 << 2)

/****************************************************************************
 * Public Function Prototypes
 ****************************************************************************/

/****************************************************************************
 * Name: getrandom
 *
 * Description:
 *   Fill a buffer of arbitrary length with randomness. This uses
 *   either /dev/random (if GRND_RANDOM flag) or /dev/urandom device and
 *   is therefore susceptible for things like the attacker exhausting file
 *   descriptors on purpose.
 *
 * Input Parameters:
 *   bytes  - Buffer for returned random bytes
 *   nbytes - Number of bytes requested.
 *   flags  - Bit mask that can contain zero or more of the ORed values
 *            together.
 *
 * Returned Value:
 *   On success, getrandom() returns the number of bytes that were copied
 *   to the buffer bytes.  This may be less than the number of bytes
 *   requested via nbytes if either GRND_RANDOM was specified in flags and
 *   insufficient entropy was present in the random source or the system
 *   call was interrupted by a signal.
 *
 *   On error, -1 is returned, and errno is set appropriately.
 *
 ****************************************************************************/

ssize_t getrandom(FAR void *bytes, size_t nbytes, unsigned int flags);

#endif /* __INCLUDE_SYS_RANDOM_H */