164 lines
3.8 KiB
C
164 lines
3.8 KiB
C
/*
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* Randomness driver for virtio
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* Copyright (C) 2007, 2008 Rusty Russell IBM Corporation
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#include <linux/err.h>
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#include <linux/hw_random.h>
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#include <linux/scatterlist.h>
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#include <linux/spinlock.h>
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#include <linux/virtio.h>
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#include <linux/virtio_rng.h>
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/* The host will fill any buffer we give it with sweet, sweet randomness. We
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* give it 64 bytes at a time, and the hwrng framework takes it 4 bytes at a
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* time. */
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#define RANDOM_DATA_SIZE 64
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static struct virtqueue *vq;
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static u32 *random_data;
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static unsigned int data_left;
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static DECLARE_COMPLETION(have_data);
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static void random_recv_done(struct virtqueue *vq)
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{
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unsigned int len;
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/* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */
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if (!vq->vq_ops->get_buf(vq, &len))
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return;
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data_left += len;
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complete(&have_data);
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}
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static void register_buffer(void)
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{
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struct scatterlist sg;
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sg_init_one(&sg, random_data+data_left, RANDOM_DATA_SIZE-data_left);
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/* There should always be room for one buffer. */
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if (vq->vq_ops->add_buf(vq, &sg, 0, 1, random_data) < 0)
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BUG();
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vq->vq_ops->kick(vq);
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}
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/* At least we don't udelay() in a loop like some other drivers. */
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static int virtio_data_present(struct hwrng *rng, int wait)
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{
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if (data_left >= sizeof(u32))
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return 1;
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again:
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if (!wait)
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return 0;
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wait_for_completion(&have_data);
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/* Not enough? Re-register. */
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if (unlikely(data_left < sizeof(u32))) {
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register_buffer();
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goto again;
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}
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return 1;
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}
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/* virtio_data_present() must have succeeded before this is called. */
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static int virtio_data_read(struct hwrng *rng, u32 *data)
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{
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BUG_ON(data_left < sizeof(u32));
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data_left -= sizeof(u32);
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*data = random_data[data_left / 4];
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if (data_left < sizeof(u32)) {
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init_completion(&have_data);
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register_buffer();
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}
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return sizeof(*data);
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}
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static struct hwrng virtio_hwrng = {
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.name = "virtio",
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.data_present = virtio_data_present,
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.data_read = virtio_data_read,
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};
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static int virtrng_probe(struct virtio_device *vdev)
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{
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int err;
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/* We expect a single virtqueue. */
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vq = virtio_find_single_vq(vdev, random_recv_done, "input");
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if (IS_ERR(vq))
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return PTR_ERR(vq);
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err = hwrng_register(&virtio_hwrng);
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if (err) {
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vdev->config->del_vqs(vdev);
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return err;
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}
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register_buffer();
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return 0;
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}
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static void __devexit virtrng_remove(struct virtio_device *vdev)
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{
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vdev->config->reset(vdev);
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hwrng_unregister(&virtio_hwrng);
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vdev->config->del_vqs(vdev);
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}
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static struct virtio_device_id id_table[] = {
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{ VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID },
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{ 0 },
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};
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static struct virtio_driver virtio_rng = {
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.driver.name = KBUILD_MODNAME,
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.driver.owner = THIS_MODULE,
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.id_table = id_table,
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.probe = virtrng_probe,
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.remove = __devexit_p(virtrng_remove),
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};
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static int __init init(void)
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{
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int err;
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random_data = kmalloc(RANDOM_DATA_SIZE, GFP_KERNEL);
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if (!random_data)
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return -ENOMEM;
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err = register_virtio_driver(&virtio_rng);
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if (err)
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kfree(random_data);
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return err;
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}
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static void __exit fini(void)
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{
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kfree(random_data);
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unregister_virtio_driver(&virtio_rng);
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}
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module_init(init);
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module_exit(fini);
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MODULE_DEVICE_TABLE(virtio, id_table);
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MODULE_DESCRIPTION("Virtio random number driver");
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MODULE_LICENSE("GPL");
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