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_ids.h>
  25 #include <linux/virtio_rng.h>
  26
  27 /* The host will fill any buffer we give it with sweet, sweet randomness.  We
  28  * give it 64 bytes at a time, and the hwrng framework takes it 4 bytes at a
  29  * time. */
  30 #define RANDOM_DATA_SIZE 64
  31
  32 static struct virtqueue *vq;
  33 static u32 *random_data;
  34 static unsigned int data_left;
  35 static DECLARE_COMPLETION(have_data);
  36
  37 static void random_recv_done(struct virtqueue *vq)
  38 {
  39         unsigned int len;
  40
  41         /* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */
  42         if (!vq->vq_ops->get_buf(vq, &len))
  43                 return;
  44
  45         data_left += len;
  46         complete(&have_data);
  47 }
  48
  49 static void register_buffer(void)
  50 {
  51         struct scatterlist sg;
  52
  53         sg_init_one(&sg, random_data+data_left, RANDOM_DATA_SIZE-data_left);
  54         /* There should always be room for one buffer. */
  55         if (vq->vq_ops->add_buf(vq, &sg, 0, 1, random_data) < 0)
  56                 BUG();
  57         vq->vq_ops->kick(vq);
  58 }
  59
  60 /* At least we don't udelay() in a loop like some other drivers. */
  61 static int virtio_data_present(struct hwrng *rng, int wait)
  62 {
  63         if (data_left >= sizeof(u32))
  64                 return 1;
  65
  66 again:
  67         if (!wait)
  68                 return 0;
  69
  70         wait_for_completion(&have_data);
  71
  72         /* Not enough?  Re-register. */
  73         if (unlikely(data_left < sizeof(u32))) {
  74                 register_buffer();
  75                 goto again;
  76         }
  77
  78         return 1;
  79 }
  80
  81 /* virtio_data_present() must have succeeded before this is called. */
  82 static int virtio_data_read(struct hwrng *rng, u32 *data)
  83 {
  84         BUG_ON(data_left < sizeof(u32));
  85         data_left -= sizeof(u32);
  86         *data = random_data[data_left / 4];
  87
  88         if (data_left < sizeof(u32)) {
  89                 init_completion(&have_data);
  90                 register_buffer();
  91         }
  92         return sizeof(*data);
  93 }
  94
  95 static struct hwrng virtio_hwrng = {
  96         .name = "virtio",
  97         .data_present = virtio_data_present,
  98         .data_read = virtio_data_read,
  99 };
 100
 101 static int virtrng_probe(struct virtio_device *vdev)
 102 {
 103         int err;
 104
 105         /* We expect a single virtqueue. */
 106         vq = virtio_find_single_vq(vdev, random_recv_done, "input");
 107         if (IS_ERR(vq))
 108                 return PTR_ERR(vq);
 109
 110         err = hwrng_register(&virtio_hwrng);
 111         if (err) {
 112                 vdev->config->del_vqs(vdev);
 113                 return err;
 114         }
 115
 116         register_buffer();
 117         return 0;
 118 }
 119
 120 static void virtrng_remove(struct virtio_device *vdev)
 121 {
 122         vdev->config->reset(vdev);
 123         hwrng_unregister(&virtio_hwrng);
 124         vdev->config->del_vqs(vdev);
 125 }
 126
 127 static struct virtio_device_id id_table[] = {
 128         { VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID },
 129         { 0 },
 130 };
 131
 132 static struct virtio_driver virtio_rng = {
 133         .driver.name =  KBUILD_MODNAME,
 134         .driver.owner = THIS_MODULE,
 135         .id_table =     id_table,
 136         .probe =        virtrng_probe,
 137         .remove =       __devexit_p(virtrng_remove),
 138 };
 139
 140 static int __init init(void)
 141 {
 142         int err;
 143
 144         random_data = kmalloc(RANDOM_DATA_SIZE, GFP_KERNEL);
 145         if (!random_data)
 146                 return -ENOMEM;
 147
 148         err = register_virtio_driver(&virtio_rng);
 149         if (err)
 150                 kfree(random_data);
 151         return err;
 152 }
 153
 154 static void __exit fini(void)
 155 {
 156         kfree(random_data);
 157         unregister_virtio_driver(&virtio_rng);
 158 }
 159 module_init(init);
 160 module_exit(fini);
 161
 162 MODULE_DEVICE_TABLE(virtio, id_table);
 163 MODULE_DESCRIPTION("Virtio random number driver");
 164 MODULE_LICENSE("GPL");