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f7f510ec RR |
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 | { | |
594de1dd | 38 | unsigned int len; |
f7f510ec | 39 | |
e5b89542 | 40 | /* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */ |
f7f510ec | 41 | if (!vq->vq_ops->get_buf(vq, &len)) |
e5b89542 | 42 | return; |
f7f510ec | 43 | |
594de1dd | 44 | data_left += len; |
f7f510ec RR |
45 | complete(&have_data); |
46 | } | |
47 | ||
48 | static void register_buffer(void) | |
49 | { | |
50 | struct scatterlist sg; | |
51 | ||
594de1dd | 52 | sg_init_one(&sg, random_data+data_left, RANDOM_DATA_SIZE-data_left); |
f7f510ec RR |
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 | { | |
594de1dd | 62 | if (data_left >= sizeof(u32)) |
f7f510ec RR |
63 | return 1; |
64 | ||
594de1dd | 65 | again: |
f7f510ec RR |
66 | if (!wait) |
67 | return 0; | |
68 | ||
69 | wait_for_completion(&have_data); | |
594de1dd RR |
70 | |
71 | /* Not enough? Re-register. */ | |
72 | if (unlikely(data_left < sizeof(u32))) { | |
73 | register_buffer(); | |
74 | goto again; | |
75 | } | |
76 | ||
f7f510ec RR |
77 | return 1; |
78 | } | |
79 | ||
80 | /* virtio_data_present() must have succeeded before this is called. */ | |
81 | static int virtio_data_read(struct hwrng *rng, u32 *data) | |
82 | { | |
594de1dd RR |
83 | BUG_ON(data_left < sizeof(u32)); |
84 | data_left -= sizeof(u32); | |
85 | *data = random_data[data_left / 4]; | |
f7f510ec | 86 | |
594de1dd | 87 | if (data_left < sizeof(u32)) { |
f7f510ec RR |
88 | init_completion(&have_data); |
89 | register_buffer(); | |
90 | } | |
91 | return sizeof(*data); | |
92 | } | |
93 | ||
94 | static struct hwrng virtio_hwrng = { | |
95 | .name = "virtio", | |
96 | .data_present = virtio_data_present, | |
97 | .data_read = virtio_data_read, | |
98 | }; | |
99 | ||
100 | static int virtrng_probe(struct virtio_device *vdev) | |
101 | { | |
102 | int err; | |
103 | ||
104 | /* We expect a single virtqueue. */ | |
d2a7ddda | 105 | vq = virtio_find_single_vq(vdev, random_recv_done, "input"); |
f7f510ec RR |
106 | if (IS_ERR(vq)) |
107 | return PTR_ERR(vq); | |
108 | ||
109 | err = hwrng_register(&virtio_hwrng); | |
110 | if (err) { | |
d2a7ddda | 111 | vdev->config->del_vqs(vdev); |
f7f510ec RR |
112 | return err; |
113 | } | |
114 | ||
115 | register_buffer(); | |
116 | return 0; | |
117 | } | |
118 | ||
119 | static void virtrng_remove(struct virtio_device *vdev) | |
120 | { | |
121 | vdev->config->reset(vdev); | |
122 | hwrng_unregister(&virtio_hwrng); | |
d2a7ddda | 123 | vdev->config->del_vqs(vdev); |
f7f510ec RR |
124 | } |
125 | ||
126 | static struct virtio_device_id id_table[] = { | |
127 | { VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID }, | |
128 | { 0 }, | |
129 | }; | |
130 | ||
131 | static struct virtio_driver virtio_rng = { | |
132 | .driver.name = KBUILD_MODNAME, | |
133 | .driver.owner = THIS_MODULE, | |
134 | .id_table = id_table, | |
135 | .probe = virtrng_probe, | |
136 | .remove = __devexit_p(virtrng_remove), | |
137 | }; | |
138 | ||
139 | static int __init init(void) | |
140 | { | |
141 | int err; | |
142 | ||
143 | random_data = kmalloc(RANDOM_DATA_SIZE, GFP_KERNEL); | |
144 | if (!random_data) | |
145 | return -ENOMEM; | |
146 | ||
147 | err = register_virtio_driver(&virtio_rng); | |
148 | if (err) | |
149 | kfree(random_data); | |
150 | return err; | |
151 | } | |
152 | ||
153 | static void __exit fini(void) | |
154 | { | |
155 | kfree(random_data); | |
156 | unregister_virtio_driver(&virtio_rng); | |
157 | } | |
158 | module_init(init); | |
159 | module_exit(fini); | |
160 | ||
161 | MODULE_DEVICE_TABLE(virtio, id_table); | |
162 | MODULE_DESCRIPTION("Virtio random number driver"); | |
163 | MODULE_LICENSE("GPL"); |