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 unsigned int len; 39 40 /* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */ 41 if (!vq->vq_ops->get_buf(vq, &len)) 42 return; 43 44 data_left += len; 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+data_left, RANDOM_DATA_SIZE-data_left); 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 >= sizeof(u32)) 63 return 1; 64 65 again: 66 if (!wait) 67 return 0; 68 69 wait_for_completion(&have_data); 70 71 /* Not enough? Re-register. */ 72 if (unlikely(data_left < sizeof(u32))) { 73 register_buffer(); 74 goto again; 75 } 76 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 { 83 BUG_ON(data_left < sizeof(u32)); 84 data_left -= sizeof(u32); 85 *data = random_data[data_left / 4]; 86 87 if (data_left < sizeof(u32)) { 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. */ 105 vq = virtio_find_single_vq(vdev, random_recv_done, "input"); 106 if (IS_ERR(vq)) 107 return PTR_ERR(vq); 108 109 err = hwrng_register(&virtio_hwrng); 110 if (err) { 111 vdev->config->del_vqs(vdev); 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); 123 vdev->config->del_vqs(vdev); 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"); 164