xref: /openbmc/linux/arch/um/drivers/random.c (revision b6dcefde)
1 /* Copyright (C) 2005 - 2008 Jeff Dike <jdike@{linux.intel,addtoit}.com> */
2 
3 /* Much of this ripped from drivers/char/hw_random.c, see there for other
4  * copyright.
5  *
6  * This software may be used and distributed according to the terms
7  * of the GNU General Public License, incorporated herein by reference.
8  */
9 #include <linux/sched.h>
10 #include <linux/module.h>
11 #include <linux/fs.h>
12 #include <linux/interrupt.h>
13 #include <linux/miscdevice.h>
14 #include <linux/delay.h>
15 #include <asm/uaccess.h>
16 #include "irq_kern.h"
17 #include "os.h"
18 
19 /*
20  * core module and version information
21  */
22 #define RNG_VERSION "1.0.0"
23 #define RNG_MODULE_NAME "hw_random"
24 
25 #define RNG_MISCDEV_MINOR		183 /* official */
26 
27 /* Changed at init time, in the non-modular case, and at module load
28  * time, in the module case.  Presumably, the module subsystem
29  * protects against a module being loaded twice at the same time.
30  */
31 static int random_fd = -1;
32 static DECLARE_WAIT_QUEUE_HEAD(host_read_wait);
33 
34 static int rng_dev_open (struct inode *inode, struct file *filp)
35 {
36 	/* enforce read-only access to this chrdev */
37 	if ((filp->f_mode & FMODE_READ) == 0)
38 		return -EINVAL;
39 	if ((filp->f_mode & FMODE_WRITE) != 0)
40 		return -EINVAL;
41 
42 	return 0;
43 }
44 
45 static atomic_t host_sleep_count = ATOMIC_INIT(0);
46 
47 static ssize_t rng_dev_read (struct file *filp, char __user *buf, size_t size,
48 			     loff_t *offp)
49 {
50 	u32 data;
51 	int n, ret = 0, have_data;
52 
53 	while (size) {
54 		n = os_read_file(random_fd, &data, sizeof(data));
55 		if (n > 0) {
56 			have_data = n;
57 			while (have_data && size) {
58 				if (put_user((u8) data, buf++)) {
59 					ret = ret ? : -EFAULT;
60 					break;
61 				}
62 				size--;
63 				ret++;
64 				have_data--;
65 				data >>= 8;
66 			}
67 		}
68 		else if (n == -EAGAIN) {
69 			DECLARE_WAITQUEUE(wait, current);
70 
71 			if (filp->f_flags & O_NONBLOCK)
72 				return ret ? : -EAGAIN;
73 
74 			atomic_inc(&host_sleep_count);
75 			reactivate_fd(random_fd, RANDOM_IRQ);
76 			add_sigio_fd(random_fd);
77 
78 			add_wait_queue(&host_read_wait, &wait);
79 			set_task_state(current, TASK_INTERRUPTIBLE);
80 
81 			schedule();
82 			set_task_state(current, TASK_RUNNING);
83 			remove_wait_queue(&host_read_wait, &wait);
84 
85 			if (atomic_dec_and_test(&host_sleep_count)) {
86 				ignore_sigio_fd(random_fd);
87 				deactivate_fd(random_fd, RANDOM_IRQ);
88 			}
89 		}
90 		else
91 			return n;
92 
93 		if (signal_pending (current))
94 			return ret ? : -ERESTARTSYS;
95 	}
96 	return ret;
97 }
98 
99 static const struct file_operations rng_chrdev_ops = {
100 	.owner		= THIS_MODULE,
101 	.open		= rng_dev_open,
102 	.read		= rng_dev_read,
103 };
104 
105 /* rng_init shouldn't be called more than once at boot time */
106 static struct miscdevice rng_miscdev = {
107 	RNG_MISCDEV_MINOR,
108 	RNG_MODULE_NAME,
109 	&rng_chrdev_ops,
110 };
111 
112 static irqreturn_t random_interrupt(int irq, void *data)
113 {
114 	wake_up(&host_read_wait);
115 
116 	return IRQ_HANDLED;
117 }
118 
119 /*
120  * rng_init - initialize RNG module
121  */
122 static int __init rng_init (void)
123 {
124 	int err;
125 
126 	err = os_open_file("/dev/random", of_read(OPENFLAGS()), 0);
127 	if (err < 0)
128 		goto out;
129 
130 	random_fd = err;
131 
132 	err = um_request_irq(RANDOM_IRQ, random_fd, IRQ_READ, random_interrupt,
133 			     IRQF_DISABLED | IRQF_SAMPLE_RANDOM, "random",
134 			     NULL);
135 	if (err)
136 		goto err_out_cleanup_hw;
137 
138 	sigio_broken(random_fd, 1);
139 
140 	err = misc_register (&rng_miscdev);
141 	if (err) {
142 		printk (KERN_ERR RNG_MODULE_NAME ": misc device register "
143 			"failed\n");
144 		goto err_out_cleanup_hw;
145 	}
146 out:
147 	return err;
148 
149 err_out_cleanup_hw:
150 	os_close_file(random_fd);
151 	random_fd = -1;
152 	goto out;
153 }
154 
155 /*
156  * rng_cleanup - shutdown RNG module
157  */
158 static void __exit rng_cleanup (void)
159 {
160 	os_close_file(random_fd);
161 	misc_deregister (&rng_miscdev);
162 }
163 
164 module_init (rng_init);
165 module_exit (rng_cleanup);
166 
167 MODULE_DESCRIPTION("UML Host Random Number Generator (RNG) driver");
168 MODULE_LICENSE("GPL");
169