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 (!vq->vq_ops->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 (vq->vq_ops->add_buf(vq, &sg, 0, 1, buf) < 0)
50 		BUG();
51 
52 	vq->vq_ops->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 = {
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);
128 }
129 
130 static void __exit fini(void)
131 {
132 	unregister_virtio_driver(&virtio_rng);
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