drivers/char/hw_random/virtio-rng.c

   1 /*
   2  * Randomness driver for virtio
   3  *  Copyright (C) 2007, 2008 Rusty Russell IBM Corporation
   4  *
   5  *  This program is free software; you can redistribute it and/or modify
   6  *  it under the terms of the GNU General Public License as published by
   7  *  the Free Software Foundation; either version 2 of the License, or
   8  *  (at your option) any later version.
   9  *
  10  *  This program is distributed in the hope that it will be useful,
  11  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  *  GNU General Public License for more details.
  14  *
  15  *  You should have received a copy of the GNU General Public License
  16  *  along with this program; if not, write to the Free Software
  17  *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
  18  */
  19 #include <linux/err.h>
  20 #include <linux/hw_random.h>
  21 #include <linux/scatterlist.h>
  22 #include <linux/spinlock.h>
  23 #include <linux/virtio.h>
  24 #include <linux/virtio_rng.h>
  25
  26 /* The host will fill any buffer we give it with sweet, sweet randomness.  We
  27  * give it 64 bytes at a time, and the hwrng framework takes it 4 bytes at a
  28  * time. */
  29 #define RANDOM_DATA_SIZE 64
  30
  31 static struct virtqueue *vq;
  32 static u32 *random_data;
  33 static unsigned int data_left;
  34 static DECLARE_COMPLETION(have_data);
  35
  36 static void random_recv_done(struct virtqueue *vq)
  37 {
  38         int len;
  39
  40         /* We never get spurious callbacks. */
  41         if (!vq->vq_ops->get_buf(vq, &len))
  42                 BUG();
  43
  44         data_left = len / sizeof(random_data[0]);
  45         complete(&have_data);
  46 }
  47
  48 static void register_buffer(void)
  49 {
  50         struct scatterlist sg;
  51
  52         sg_init_one(&sg, random_data, RANDOM_DATA_SIZE);
  53         /* There should always be room for one buffer. */
  54         if (vq->vq_ops->add_buf(vq, &sg, 0, 1, random_data) != 0)
  55                 BUG();
  56         vq->vq_ops->kick(vq);
  57 }
  58
  59 /* At least we don't udelay() in a loop like some other drivers. */
  60 static int virtio_data_present(struct hwrng *rng, int wait)
  61 {
  62         if (data_left)
  63                 return 1;
  64
  65         if (!wait)
  66                 return 0;
  67
  68         wait_for_completion(&have_data);
  69         return 1;
  70 }
  71
  72 /* virtio_data_present() must have succeeded before this is called. */
  73 static int virtio_data_read(struct hwrng *rng, u32 *data)
  74 {
  75         BUG_ON(!data_left);
  76
  77         *data = random_data[--data_left];
  78
  79         if (!data_left) {
  80                 init_completion(&have_data);
  81                 register_buffer();
  82         }
  83         return sizeof(*data);
  84 }
  85
  86 static struct hwrng virtio_hwrng = {
  87         .name = "virtio",
  88         .data_present = virtio_data_present,
  89         .data_read = virtio_data_read,
  90 };
  91
  92 static int virtrng_probe(struct virtio_device *vdev)
  93 {
  94         int err;
  95
  96         /* We expect a single virtqueue. */
  97         vq = vdev->config->find_vq(vdev, 0, random_recv_done);
  98         if (IS_ERR(vq))
  99                 return PTR_ERR(vq);
 100
 101         err = hwrng_register(&virtio_hwrng);
 102         if (err) {
 103                 vdev->config->del_vq(vq);
 104                 return err;
 105         }
 106
 107         register_buffer();
 108         return 0;
 109 }
 110
 111 static void virtrng_remove(struct virtio_device *vdev)
 112 {
 113         vdev->config->reset(vdev);
 114         hwrng_unregister(&virtio_hwrng);
 115         vdev->config->del_vq(vq);
 116 }
 117
 118 static struct virtio_device_id id_table[] = {
 119         { VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID },
 120         { 0 },
 121 };
 122
 123 static struct virtio_driver virtio_rng = {
 124         .driver.name =  KBUILD_MODNAME,
 125         .driver.owner = THIS_MODULE,
 126         .id_table =     id_table,
 127         .probe =        virtrng_probe,
 128         .remove =       __devexit_p(virtrng_remove),
 129 };
 130
 131 static int __init init(void)
 132 {
 133         int err;
 134
 135         random_data = kmalloc(RANDOM_DATA_SIZE, GFP_KERNEL);
 136         if (!random_data)
 137                 return -ENOMEM;
 138
 139         err = register_virtio_driver(&virtio_rng);
 140         if (err)
 141                 kfree(random_data);
 142         return err;
 143 }
 144
 145 static void __exit fini(void)
 146 {
 147         kfree(random_data);
 148         unregister_virtio_driver(&virtio_rng);
 149 }
 150 module_init(init);
 151 module_exit(fini);
 152
 153 MODULE_DEVICE_TABLE(virtio, id_table);
 154 MODULE_DESCRIPTION("Virtio random number driver");
 155 MODULE_LICENSE("GPL");