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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>
/* The host will fill any buffer we give it with sweet, sweet randomness. We
* give it 64 bytes at a time, and the hwrng framework takes it 4 bytes at a
* time. */
#define RANDOM_DATA_SIZE 64
static struct virtqueue *vq;
static u32 *random_data;
static unsigned int data_left;
static DECLARE_COMPLETION(have_data);
static void random_recv_done(struct virtqueue *vq)
{
unsigned int len;
/* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */
if (!vq->vq_ops->get_buf(vq, &len))
return;
data_left += len;
complete(&have_data);
}
static void register_buffer(void)
{
struct scatterlist sg;
sg_init_one(&sg, random_data+data_left, RANDOM_DATA_SIZE-data_left);
/* There should always be room for one buffer. */
if (vq->vq_ops->add_buf(vq, &sg, 0, 1, random_data) != 0)
BUG();
vq->vq_ops->kick(vq);
}
/* At least we don't udelay() in a loop like some other drivers. */
static int virtio_data_present(struct hwrng *rng, int wait)
{
if (data_left >= sizeof(u32))
return 1;
again:
if (!wait)
return 0;
wait_for_completion(&have_data);
/* Not enough? Re-register. */
if (unlikely(data_left < sizeof(u32))) {
register_buffer();
goto again;
}
return 1;
}
/* virtio_data_present() must have succeeded before this is called. */
static int virtio_data_read(struct hwrng *rng, u32 *data)
{
BUG_ON(data_left < sizeof(u32));
data_left -= sizeof(u32);
*data = random_data[data_left / 4];
if (data_left < sizeof(u32)) {
init_completion(&have_data);
register_buffer();
}
return sizeof(*data);
}
static struct hwrng virtio_hwrng = {
.name = "virtio",
.data_present = virtio_data_present,
.data_read = virtio_data_read,
};
static int virtrng_probe(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;
}
register_buffer();
return 0;
}
static void virtrng_remove(struct virtio_device *vdev)
{
vdev->config->reset(vdev);
hwrng_unregister(&virtio_hwrng);
vdev->config->del_vqs(vdev);
}
static struct virtio_device_id id_table[] = {
{ VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID },
{ 0 },
};
static struct virtio_driver virtio_rng = {
.driver.name = KBUILD_MODNAME,
.driver.owner = THIS_MODULE,
.id_table = id_table,
.probe = virtrng_probe,
.remove = __devexit_p(virtrng_remove),
};
static int __init init(void)
{
int err;
random_data = kmalloc(RANDOM_DATA_SIZE, GFP_KERNEL);
if (!random_data)
return -ENOMEM;
err = register_virtio_driver(&virtio_rng);
if (err)
kfree(random_data);
return err;
}
static void __exit fini(void)
{
kfree(random_data);
unregister_virtio_driver(&virtio_rng);
}
module_init(init);
module_exit(fini);
MODULE_DEVICE_TABLE(virtio, id_table);
MODULE_DESCRIPTION("Virtio random number driver");
MODULE_LICENSE("GPL");
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