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         virtqueue_add_inbuf(vq, &sg, 1, buf, GFP_KERNEL);
  51
  52         virtqueue_kick(vq);
  53 }
  54
  55 static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait)
  56 {
  57         int ret;
  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         ret = wait_for_completion_killable(&have_data);
  69         if (ret < 0)
  70                 return ret;
  71
  72         busy = false;
  73
  74         return data_avail;
  75 }
  76
  77 static void virtio_cleanup(struct hwrng *rng)
  78 {
  79         if (busy)
  80                 wait_for_completion(&have_data);
  81 }
  82
  83
  84 static struct hwrng virtio_hwrng = {
  85         .name           = "virtio",
  86         .cleanup        = virtio_cleanup,
  87         .read           = virtio_read,
  88 };
  89
  90 static int probe_common(struct virtio_device *vdev)
  91 {
  92         int err;
  93
  94         if (vq) {
  95                 /* We only support one device for now */
  96                 return -EBUSY;
  97         }
  98         /* We expect a single virtqueue. */
  99         vq = virtio_find_single_vq(vdev, random_recv_done, "input");
 100         if (IS_ERR(vq)) {
 101                 err = PTR_ERR(vq);
 102                 vq = NULL;
 103                 return err;
 104         }
 105
 106         err = hwrng_register(&virtio_hwrng);
 107         if (err) {
 108                 vdev->config->del_vqs(vdev);
 109                 vq = NULL;
 110                 return err;
 111         }
 112
 113         return 0;
 114 }
 115
 116 static void remove_common(struct virtio_device *vdev)
 117 {
 118         vdev->config->reset(vdev);
 119         busy = false;
 120         hwrng_unregister(&virtio_hwrng);
 121         vdev->config->del_vqs(vdev);
 122         vq = NULL;
 123 }
 124
 125 static int virtrng_probe(struct virtio_device *vdev)
 126 {
 127         return probe_common(vdev);
 128 }
 129
 130 static void virtrng_remove(struct virtio_device *vdev)
 131 {
 132         remove_common(vdev);
 133 }
 134
 135 #ifdef CONFIG_PM_SLEEP
 136 static int virtrng_freeze(struct virtio_device *vdev)
 137 {
 138         remove_common(vdev);
 139         return 0;
 140 }
 141
 142 static int virtrng_restore(struct virtio_device *vdev)
 143 {
 144         return probe_common(vdev);
 145 }
 146 #endif
 147
 148 static struct virtio_device_id id_table[] = {
 149         { VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID },
 150         { 0 },
 151 };
 152
 153 static struct virtio_driver virtio_rng_driver = {
 154         .driver.name =  KBUILD_MODNAME,
 155         .driver.owner = THIS_MODULE,
 156         .id_table =     id_table,
 157         .probe =        virtrng_probe,
 158         .remove =       virtrng_remove,
 159 #ifdef CONFIG_PM_SLEEP
 160         .freeze =       virtrng_freeze,
 161         .restore =      virtrng_restore,
 162 #endif
 163 };
 164
 165 module_virtio_driver(virtio_rng_driver);
 166 MODULE_DEVICE_TABLE(virtio, id_table);
 167 MODULE_DESCRIPTION("Virtio random number driver");
 168 MODULE_LICENSE("GPL");