FreeBSD/Linux Kernel Cross Reference
sys/dev/random/fenestrasX/fx_pub.h

     /*-
      * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
      *
      * Copyright (c) 2019 Conrad Meyer <cem@FreeBSD.org>
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
      * are met:
      * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     * $FreeBSD$
     */
    #pragma once
    
    #include <sys/systm.h>
    
    /*
     * The root BRNG seed version, or generation.
     *
     * FenestrasX-aware downstream CSPRNGs (i.e., arc4random(9)) should track the
     * generation number they seeded from, using the read_random_key(9) API below.
     * If their current seed version is older than the root generation, they should
     * reseed before producing output.
     *
     * The variable is read-only outside of the fenestrasX implementation and
     * should be accessed using 'atomic_load_acq_64(&fxrng_root_generation)'.
     * Reseeds are extremely infrequent, so callers may wish to hint to the
     * compiler that a matching generation is the expected case, with
     * __predict_true() or __predict_false().
     */
    extern uint64_t __read_mostly fxrng_root_generation;
    
    /*
     * A routine for generating seed/key material 
     * Bypasses random(4) for now, but conceivably could be incorporated into that.
     */
    void read_random_key(void *buf, size_t nbytes, uint64_t *seed_version_out);

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