libvirt/src/util/virrandom.c

/*
 * Copyright (C) 2012-2013 Red Hat, Inc.
 *
 * This 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.
 *
 * This 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 this library.  If not, see
 * <http://www.gnu.org/licenses/>.
 *
 * Authors:
 *     Daniel P. Berrange <berrange@redhat.com>
 */

#include <config.h>

#include <stdlib.h>
#include <inttypes.h>
#include <math.h>
#include <strings.h>

#include "virrandom.h"
#include "virthread.h"
#include "count-one-bits.h"
#include "virutil.h"
#include "virerror.h"
#include "virlog.h"
#include "virstring.h"

#define VIR_FROM_THIS VIR_FROM_NONE

/* The algorithm of virRandomBits relies on gnulib's guarantee that
 * 'random_r' matches the POSIX requirements on 'random' of being
 * evenly distributed among exactly [0, 2**31) (that is, we always get
 * exactly 31 bits).  While this happens to be the value of RAND_MAX
 * on glibc, note that POSIX only requires RAND_MAX to be tied to the
 * weaker 'rand', so there are platforms where RAND_MAX is smaller
 * than the range of 'random_r'.  For the results to be evenly
 * distributed among up to 64 bits, we also rely on the period of
 * 'random_r' to be at least 2**64, which POSIX only guarantees for
 * 'random' if you use 256 bytes of state.  */
enum {
    RANDOM_BITS_PER_ITER = 31,
    RANDOM_BITS_MASK = (1U << RANDOM_BITS_PER_ITER) - 1,
    RANDOM_STATE_SIZE = 256,
};

static char randomState[RANDOM_STATE_SIZE];
static struct random_data randomData;
static virMutex randomLock;


static int
virRandomOnceInit(void)
{
    unsigned int seed = time(NULL) ^ getpid();

#if 0
    /* Normally we want a decent seed.  But if reproducible debugging
     * of a fixed pseudo-random sequence is ever required, uncomment
     * this block to let an environment variable force the seed.  */
    const char *debug = getenv("VIR_DEBUG_RANDOM_SEED");

    if (debug && virStrToLong_ui(debug, NULL, 0, &seed) < 0)
        return -1;
#endif

    if (virMutexInit(&randomLock) < 0)
        return -1;

    if (initstate_r(seed,
                    randomState,
                    sizeof(randomState),
                    &randomData) < 0)
        return -1;

    return 0;
}

VIR_ONCE_GLOBAL_INIT(virRandom)

/**
 * virRandomBits:
 * @nbits: Number of bits of randommess required
 *
 * Generate an evenly distributed random number between [0,2^nbits), where
 * @nbits must be in the range (0,64].
 *
 * Return: a random number with @nbits entropy
 */
uint64_t virRandomBits(int nbits)
{
    uint64_t ret = 0;
    int32_t bits;

    if (virRandomInitialize() < 0) {
        /* You're already hosed, so this particular non-random value
         * isn't any worse.  */
        VIR_WARN("random number generation is broken");
        return 0;
    }

    virMutexLock(&randomLock);

    while (nbits > RANDOM_BITS_PER_ITER) {
        random_r(&randomData, &bits);
        ret = (ret << RANDOM_BITS_PER_ITER) | (bits & RANDOM_BITS_MASK);
        nbits -= RANDOM_BITS_PER_ITER;
    }

    random_r(&randomData, &bits);
    ret = (ret << nbits) | (bits & ((1 << nbits) - 1));

    virMutexUnlock(&randomLock);
    return ret;
}


/**
 * virRandom:
 *
 * Generate an evenly distributed random number between [0.0,1.0)
 *
 * Return: a random number with 48 bits of entropy
 */
double virRandom(void)
{
    uint64_t val = virRandomBits(48);

    return ldexp(val, -48);
}


/**
 * virRandomInt:
 * @max: upper limit
 *
 * Generate an evenly distributed random integer between [0, @max)
 *
 * Return: a random number between [0,@max)
 */
uint32_t virRandomInt(uint32_t max)
{
    if ((max & (max - 1)) == 0)
        return virRandomBits(ffs(max) - 1);

    double val = virRandom();
    return val * max;
}


#define QUMRANET_OUI "001a4a"
#define VMWARE_OUI "000569"
#define MICROSOFT_OUI "0050f2"
#define XEN_OUI "00163e"

int
virRandomGenerateWWN(char **wwn,
                     const char *virt_type) {
    const char *oui = NULL;

    if (!virt_type) {
        virReportError(VIR_ERR_INVALID_ARG, "%s",
                       _("argument virt_type must not be NULL"));
        return -1;
    }

    if (STREQ(virt_type, "QEMU")) {
        oui = QUMRANET_OUI;
    } else if (STREQ(virt_type, "Xen") ||
               STREQ(virt_type, "xenlight") ||
               STREQ(virt_type, "XenAPI")) {
        oui = XEN_OUI;
    } else if (STREQ(virt_type, "ESX") ||
               STREQ(virt_type, "VMWARE")) {
        oui = VMWARE_OUI;
    } else if (STREQ(virt_type, "HYPER-V")) {
        oui = MICROSOFT_OUI;
    } else {
        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
                       _("Unsupported virt type"));
        return -1;
    }

    if (virAsprintf(wwn, "5" "%s%09llx", oui,
                    (unsigned long long)virRandomBits(36)) < 0)
        return -1;
    return 0;
}