virtio-rng.c

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/*
 * Randomness driver for virtio
 *  Copyright (C) 2007, 2008 Rusty Russell IBM Corporation
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program 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 General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
 */

#include <linux/err.h>
#include <linux/hw_random.h>
#include <linux/scatterlist.h>
#include <linux/spinlock.h>
#include <linux/virtio.h>
#include <linux/virtio_rng.h>
#include <linux/module.h>

static struct virtqueue *vq;
static unsigned int data_avail;
static DECLARE_COMPLETION(have_data);
static bool busy;

static void random_recv_done(struct virtqueue *vq)
{
    /* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */
    if (!virtqueue_get_buf(vq, &data_avail))
        return;

    complete(&have_data);
}

/* The host will fill any buffer we give it with sweet, sweet randomness. */
static void register_buffer(u8 *buf, size_t size)
{
    struct scatterlist sg;

    sg_init_one(&sg, buf, size);

    /* There should always be room for one buffer. */
    if (virtqueue_add_buf(vq, &sg, 0, 1, buf, GFP_KERNEL) < 0)
        BUG();

    virtqueue_kick(vq);
}

static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait)
{
    int ret;

    if (!busy) {
        busy = true;
        init_completion(&have_data);
        register_buffer(buf, size);
    }

    if (!wait)
        return 0;

    ret = wait_for_completion_killable(&have_data);
    if (ret < 0)
        return ret;

    busy = false;

    return data_avail;
}

static void virtio_cleanup(struct hwrng *rng)
{
    if (busy)
        wait_for_completion(&have_data);
}


static struct hwrng virtio_hwrng = {
    .name       = "virtio",
    .cleanup    = virtio_cleanup,
    .read       = virtio_read,
};

static int probe_common(struct virtio_device *vdev)
{
    int err;

    /* We expect a single virtqueue. */
    vq = virtio_find_single_vq(vdev, random_recv_done, "input");
    if (IS_ERR(vq))
        return PTR_ERR(vq);

    err = hwrng_register(&virtio_hwrng);
    if (err) {
        vdev->config->del_vqs(vdev);
        return err;
    }

    return 0;
}

static void remove_common(struct virtio_device *vdev)
{
    vdev->config->reset(vdev);
    busy = false;
    hwrng_unregister(&virtio_hwrng);
    vdev->config->del_vqs(vdev);
}

static int virtrng_probe(struct virtio_device *vdev)
{
    return probe_common(vdev);
}

static void __devexit virtrng_remove(struct virtio_device *vdev)
{
    remove_common(vdev);
}

#ifdef CONFIG_PM
static int virtrng_freeze(struct virtio_device *vdev)
{
    remove_common(vdev);
    return 0;
}

static int virtrng_restore(struct virtio_device *vdev)
{
    return probe_common(vdev);
}
#endif

static struct virtio_device_id id_table[] = {
    { VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID },
    { 0 },
};

static struct virtio_driver virtio_rng_driver = {
    .driver.name =  KBUILD_MODNAME,
    .driver.owner = THIS_MODULE,
    .id_table = id_table,
    .probe =    virtrng_probe,
    .remove =   __devexit_p(virtrng_remove),
#ifdef CONFIG_PM
    .freeze =   virtrng_freeze,
    .restore =  virtrng_restore,
#endif
};

static int __init init(void)
{
    return register_virtio_driver(&virtio_rng_driver);
}

static void __exit fini(void)
{
    unregister_virtio_driver(&virtio_rng_driver);
}
module_init(init);
module_exit(fini);

MODULE_DEVICE_TABLE(virtio, id_table);
MODULE_DESCRIPTION("Virtio random number driver");
MODULE_LICENSE("GPL");