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_inbuf(vq, &sg, 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         if (vq) {
  96                 /* We only support one device for now */
  97                 return -EBUSY;
  98         }
  99         /* We expect a single virtqueue. */
 100         vq = virtio_find_single_vq(vdev, random_recv_done, "input");
 101         if (IS_ERR(vq)) {
 102                 err = PTR_ERR(vq);
 103                 vq = NULL;
 104                 return err;
 105         }
 106
 107         err = hwrng_register(&virtio_hwrng);
 108         if (err) {
 109                 vdev->config->del_vqs(vdev);
 110                 vq = NULL;
 111                 return err;
 112         }
 113
 114         return 0;
 115 }
 116
 117 static void remove_common(struct virtio_device *vdev)
 118 {
 119         vdev->config->reset(vdev);
 120         busy = false;
 121         hwrng_unregister(&virtio_hwrng);
 122         vdev->config->del_vqs(vdev);
 123         vq = NULL;
 124 }
 125
 126 static int virtrng_probe(struct virtio_device *vdev)
 127 {
 128         return probe_common(vdev);
 129 }
 130
 131 static void virtrng_remove(struct virtio_device *vdev)
 132 {
 133         remove_common(vdev);
 134 }
 135
 136 #ifdef CONFIG_PM
 137 static int virtrng_freeze(struct virtio_device *vdev)
 138 {
 139         remove_common(vdev);
 140         return 0;
 141 }
 142
 143 static int virtrng_restore(struct virtio_device *vdev)
 144 {
 145         return probe_common(vdev);
 146 }
 147 #endif
 148
 149 static struct virtio_device_id id_table[] = {
 150         { VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID },
 151         { 0 },
 152 };
 153
 154 static struct virtio_driver virtio_rng_driver = {
 155         .driver.name =  KBUILD_MODNAME,
 156         .driver.owner = THIS_MODULE,
 157         .id_table =     id_table,
 158         .probe =        virtrng_probe,
 159         .remove =       virtrng_remove,
 160 #ifdef CONFIG_PM
 161         .freeze =       virtrng_freeze,
 162         .restore =      virtrng_restore,
 163 #endif
 164 };
 165
 166 module_virtio_driver(virtio_rng_driver);
 167 MODULE_DEVICE_TABLE(virtio, id_table);
 168 MODULE_DESCRIPTION("Virtio random number driver");
 169 MODULE_LICENSE("GPL");