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
  20 #include <linux/err.h>
  21 #include <linux/hw_random.h>
  22 #include <linux/scatterlist.h>
  23 #include <linux/spinlock.h>
  24 #include <linux/virtio.h>
  25 #include <linux/virtio_rng.h>
  26 #include <linux/module.h>
  27
  28 static struct virtqueue *vq;
  29 static unsigned int data_avail;
  30 static DECLARE_COMPLETION(have_data);
  31 static bool busy;
  32
  33 static void random_recv_done(struct virtqueue *vq)
  34 {
  35         /* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */
  36         if (!virtqueue_get_buf(vq, &data_avail))
  37                 return;
  38
  39         complete(&have_data);
  40 }
  41
  42 /* The host will fill any buffer we give it with sweet, sweet randomness. */
  43 static void register_buffer(u8 *buf, size_t size)
  44 {
  45         struct scatterlist sg;
  46
  47         sg_init_one(&sg, buf, size);
  48
  49         /* There should always be room for one buffer. */
  50         if (virtqueue_add_buf(vq, &sg, 0, 1, buf, GFP_KERNEL) < 0)
  51                 BUG();
  52
  53         virtqueue_kick(vq);
  54 }
  55
  56 static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait)
  57 {
  58
  59         if (!busy) {
  60                 busy = true;
  61                 init_completion(&have_data);
  62                 register_buffer(buf, size);
  63         }
  64
  65         if (!wait)
  66                 return 0;
  67
  68         wait_for_completion(&have_data);
  69
  70         busy = false;
  71
  72         return data_avail;
  73 }
  74
  75 static void virtio_cleanup(struct hwrng *rng)
  76 {
  77         if (busy)
  78                 wait_for_completion(&have_data);
  79 }
  80
  81
  82 static struct hwrng virtio_hwrng = {
  83         .name           = "virtio",
  84         .cleanup        = virtio_cleanup,
  85         .read           = virtio_read,
  86 };
  87
  88 static int virtrng_probe(struct virtio_device *vdev)
  89 {
  90         int err;
  91
  92         if (vq) {
  93                 /* We only support one device for now */
  94                 return -EBUSY;
  95         }
  96         /* We expect a single virtqueue. */
  97         vq = virtio_find_single_vq(vdev, random_recv_done, "input");
  98         if (IS_ERR(vq)) {
  99                 err = PTR_ERR(vq);
 100                 vq = NULL;
 101                 return err;
 102         }
 103
 104         err = hwrng_register(&virtio_hwrng);
 105         if (err) {
 106                 vdev->config->del_vqs(vdev);
 107                 vq = NULL;
 108                 return err;
 109         }
 110
 111         return 0;
 112 }
 113
 114 static void __devexit virtrng_remove(struct virtio_device *vdev)
 115 {
 116         vdev->config->reset(vdev);
 117         hwrng_unregister(&virtio_hwrng);
 118         vdev->config->del_vqs(vdev);
 119         vq = NULL;
 120 }
 121
 122 static struct virtio_device_id id_table[] = {
 123         { VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID },
 124         { 0 },
 125 };
 126
 127 static struct virtio_driver virtio_rng_driver = {
 128         .driver.name =  KBUILD_MODNAME,
 129         .driver.owner = THIS_MODULE,
 130         .id_table =     id_table,
 131         .probe =        virtrng_probe,
 132         .remove =       __devexit_p(virtrng_remove),
 133 };
 134
 135 static int __init init(void)
 136 {
 137         return register_virtio_driver(&virtio_rng_driver);
 138 }
 139
 140 static void __exit fini(void)
 141 {
 142         unregister_virtio_driver(&virtio_rng_driver);
 143 }
 144 module_init(init);
 145 module_exit(fini);
 146
 147 MODULE_DEVICE_TABLE(virtio, id_table);
 148 MODULE_DESCRIPTION("Virtio random number driver");
 149 MODULE_LICENSE("GPL");