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         unsigned int len;
  39
  40         /* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */
  41         if (!vq->vq_ops->get_buf(vq, &len))
  42                 return;
  43
  44         data_left += len;
  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+data_left, RANDOM_DATA_SIZE-data_left);
  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 >= sizeof(u32))
  63                 return 1;
  64
  65 again:
  66         if (!wait)
  67                 return 0;
  68
  69         wait_for_completion(&have_data);
  70
  71         /* Not enough?  Re-register. */
  72         if (unlikely(data_left < sizeof(u32))) {
  73                 register_buffer();
  74                 goto again;
  75         }
  76
  77         return 1;
  78 }
  79
  80 /* virtio_data_present() must have succeeded before this is called. */
  81 static int virtio_data_read(struct hwrng *rng, u32 *data)
  82 {
  83         BUG_ON(data_left < sizeof(u32));
  84         data_left -= sizeof(u32);
  85         *data = random_data[data_left / 4];
  86
  87         if (data_left < sizeof(u32)) {
  88                 init_completion(&have_data);
  89                 register_buffer();
  90         }
  91         return sizeof(*data);
  92 }
  93
  94 static struct hwrng virtio_hwrng = {
  95         .name = "virtio",
  96         .data_present = virtio_data_present,
  97         .data_read = virtio_data_read,
  98 };
  99
 100 static int virtrng_probe(struct virtio_device *vdev)
 101 {
 102         int err;
 103
 104         /* We expect a single virtqueue. */
 105         vq = virtio_find_single_vq(vdev, random_recv_done, "input");
 106         if (IS_ERR(vq))
 107                 return PTR_ERR(vq);
 108
 109         err = hwrng_register(&virtio_hwrng);
 110         if (err) {
 111                 vdev->config->del_vqs(vdev);
 112                 return err;
 113         }
 114
 115         register_buffer();
 116         return 0;
 117 }
 118
 119 static void __devexit virtrng_remove(struct virtio_device *vdev)
 120 {
 121         vdev->config->reset(vdev);
 122         hwrng_unregister(&virtio_hwrng);
 123         vdev->config->del_vqs(vdev);
 124 }
 125
 126 static struct virtio_device_id id_table[] = {
 127         { VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID },
 128         { 0 },
 129 };
 130
 131 static struct virtio_driver virtio_rng = {
 132         .driver.name =  KBUILD_MODNAME,
 133         .driver.owner = THIS_MODULE,
 134         .id_table =     id_table,
 135         .probe =        virtrng_probe,
 136         .remove =       __devexit_p(virtrng_remove),
 137 };
 138
 139 static int __init init(void)
 140 {
 141         int err;
 142
 143         random_data = kmalloc(RANDOM_DATA_SIZE, GFP_KERNEL);
 144         if (!random_data)
 145                 return -ENOMEM;
 146
 147         err = register_virtio_driver(&virtio_rng);
 148         if (err)
 149                 kfree(random_data);
 150         return err;
 151 }
 152
 153 static void __exit fini(void)
 154 {
 155         kfree(random_data);
 156         unregister_virtio_driver(&virtio_rng);
 157 }
 158 module_init(init);
 159 module_exit(fini);
 160
 161 MODULE_DEVICE_TABLE(virtio, id_table);
 162 MODULE_DESCRIPTION("Virtio random number driver");
 163 MODULE_LICENSE("GPL");