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         int ret;
  59
  60         if (!busy) {
  61                 busy = true;
  62                 init_completion(&have_data);
  63                 register_buffer(buf, size);
  64         }
  65
  66         if (!wait)
  67                 return 0;
  68
  69         ret = wait_for_completion_killable(&have_data);
  70         if (ret < 0)
  71                 return ret;
  72
  73         busy = false;
  74
  75         return data_avail;
  76 }
  77
  78 static void virtio_cleanup(struct hwrng *rng)
  79 {
  80         if (busy)
  81                 wait_for_completion(&have_data);
  82 }
  83
  84
  85 static struct hwrng virtio_hwrng = {
  86         .name           = "virtio",
  87         .cleanup        = virtio_cleanup,
  88         .read           = virtio_read,
  89 };
  90
  91 static int probe_common(struct virtio_device *vdev)
  92 {
  93         int err;
  94
  95         /* We expect a single virtqueue. */
  96         vq = virtio_find_single_vq(vdev, random_recv_done, "input");
  97         if (IS_ERR(vq))
  98                 return PTR_ERR(vq);
  99
 100         err = hwrng_register(&virtio_hwrng);
 101         if (err) {
 102                 vdev->config->del_vqs(vdev);
 103                 return err;
 104         }
 105
 106         return 0;
 107 }
 108
 109 static void remove_common(struct virtio_device *vdev)
 110 {
 111         vdev->config->reset(vdev);
 112         busy = false;
 113         hwrng_unregister(&virtio_hwrng);
 114         vdev->config->del_vqs(vdev);
 115 }
 116
 117 static int virtrng_probe(struct virtio_device *vdev)
 118 {
 119         return probe_common(vdev);
 120 }
 121
 122 static void virtrng_remove(struct virtio_device *vdev)
 123 {
 124         remove_common(vdev);
 125 }
 126
 127 #ifdef CONFIG_PM
 128 static int virtrng_freeze(struct virtio_device *vdev)
 129 {
 130         remove_common(vdev);
 131         return 0;
 132 }
 133
 134 static int virtrng_restore(struct virtio_device *vdev)
 135 {
 136         return probe_common(vdev);
 137 }
 138 #endif
 139
 140 static struct virtio_device_id id_table[] = {
 141         { VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID },
 142         { 0 },
 143 };
 144
 145 static struct virtio_driver virtio_rng_driver = {
 146         .driver.name =  KBUILD_MODNAME,
 147         .driver.owner = THIS_MODULE,
 148         .id_table =     id_table,
 149         .probe =        virtrng_probe,
 150         .remove =       __devexit_p(virtrng_remove),
 151 #ifdef CONFIG_PM
 152         .freeze =       virtrng_freeze,
 153         .restore =      virtrng_restore,
 154 #endif
 155 };
 156
 157 static int __init init(void)
 158 {
 159         return register_virtio_driver(&virtio_rng_driver);
 160 }
 161
 162 static void __exit fini(void)
 163 {
 164         unregister_virtio_driver(&virtio_rng_driver);
 165 }
 166 module_init(init);
 167 module_exit(fini);
 168
 169 MODULE_DEVICE_TABLE(virtio, id_table);
 170 MODULE_DESCRIPTION("Virtio random number driver");
 171 MODULE_LICENSE("GPL");