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