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 #include <linux/err.h>
20 #include <linux/hw_random.h>
21 #include <linux/scatterlist.h>
22 #include <linux/spinlock.h>
23 #include <linux/virtio.h>
24 #include <linux/virtio_rng.h>
25 
26 /* The host will fill any buffer we give it with sweet, sweet randomness.  We
27  * give it 64 bytes at a time, and the hwrng framework takes it 4 bytes at a
28  * time. */
29 #define RANDOM_DATA_SIZE 64
30 
31 static struct virtqueue *vq;
32 static u32 *random_data;
33 static unsigned int data_left;
34 static DECLARE_COMPLETION(have_data);
35 
36 static void random_recv_done(struct virtqueue *vq)
37 {
38 	int len;
39 
40 	/* We never get spurious callbacks. */
41 	if (!vq->vq_ops->get_buf(vq, &len))
42 		BUG();
43 
44 	data_left = len / sizeof(random_data[0]);
45 	complete(&have_data);
46 }
47 
48 static void register_buffer(void)
49 {
50 	struct scatterlist sg;
51 
52 	sg_init_one(&sg, random_data, RANDOM_DATA_SIZE);
53 	/* There should always be room for one buffer. */
54 	if (vq->vq_ops->add_buf(vq, &sg, 0, 1, random_data) != 0)
55 		BUG();
56 	vq->vq_ops->kick(vq);
57 }
58 
59 /* At least we don't udelay() in a loop like some other drivers. */
60 static int virtio_data_present(struct hwrng *rng, int wait)
61 {
62 	if (data_left)
63 		return 1;
64 
65 	if (!wait)
66 		return 0;
67 
68 	wait_for_completion(&have_data);
69 	return 1;
70 }
71 
72 /* virtio_data_present() must have succeeded before this is called. */
73 static int virtio_data_read(struct hwrng *rng, u32 *data)
74 {
75 	BUG_ON(!data_left);
76 
77 	*data = random_data[--data_left];
78 
79 	if (!data_left) {
80 		init_completion(&have_data);
81 		register_buffer();
82 	}
83 	return sizeof(*data);
84 }
85 
86 static struct hwrng virtio_hwrng = {
87 	.name = "virtio",
88 	.data_present = virtio_data_present,
89 	.data_read = virtio_data_read,
90 };
91 
92 static int virtrng_probe(struct virtio_device *vdev)
93 {
94 	int err;
95 
96 	/* We expect a single virtqueue. */
97 	vq = vdev->config->find_vq(vdev, 0, random_recv_done);
98 	if (IS_ERR(vq))
99 		return PTR_ERR(vq);
100 
101 	err = hwrng_register(&virtio_hwrng);
102 	if (err) {
103 		vdev->config->del_vq(vq);
104 		return err;
105 	}
106 
107 	register_buffer();
108 	return 0;
109 }
110 
111 static void virtrng_remove(struct virtio_device *vdev)
112 {
113 	vdev->config->reset(vdev);
114 	hwrng_unregister(&virtio_hwrng);
115 	vdev->config->del_vq(vq);
116 }
117 
118 static struct virtio_device_id id_table[] = {
119 	{ VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID },
120 	{ 0 },
121 };
122 
123 static struct virtio_driver virtio_rng = {
124 	.driver.name =	KBUILD_MODNAME,
125 	.driver.owner =	THIS_MODULE,
126 	.id_table =	id_table,
127 	.probe =	virtrng_probe,
128 	.remove =	__devexit_p(virtrng_remove),
129 };
130 
131 static int __init init(void)
132 {
133 	int err;
134 
135 	random_data = kmalloc(RANDOM_DATA_SIZE, GFP_KERNEL);
136 	if (!random_data)
137 		return -ENOMEM;
138 
139 	err = register_virtio_driver(&virtio_rng);
140 	if (err)
141 		kfree(random_data);
142 	return err;
143 }
144 
145 static void __exit fini(void)
146 {
147 	kfree(random_data);
148 	unregister_virtio_driver(&virtio_rng);
149 }
150 module_init(init);
151 module_exit(fini);
152 
153 MODULE_DEVICE_TABLE(virtio, id_table);
154 MODULE_DESCRIPTION("Virtio random number driver");
155 MODULE_LICENSE("GPL");
156