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