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
random_recv_done(struct virtqueue * vq)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. */
register_buffer(u8 * buf,size_t size)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
virtio_read(struct hwrng * rng,void * buf,size_t size,bool wait)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
virtio_cleanup(struct hwrng * rng)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
virtrng_probe(struct virtio_device * vdev)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
virtrng_remove(struct virtio_device * vdev)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
init(void)125 static int __init init(void)
126 {
127 return register_virtio_driver(&virtio_rng_driver);
128 }
129
fini(void)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");
140