random.c

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/* Copyright (C) 2005 - 2008 Jeff Dike <jdike@{linux.intel,addtoit}.com> */

/* Much of this ripped from drivers/char/hw_random.c, see there for other
 * copyright.
 *
 * This software may be used and distributed according to the terms
 * of the GNU General Public License, incorporated herein by reference.
 */
#include <linux/sched.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/interrupt.h>
#include <linux/miscdevice.h>
#include <linux/delay.h>
#include <asm/uaccess.h>
#include <irq_kern.h>
#include <os.h>

/*
 * core module and version information
 */
#define RNG_VERSION "1.0.0"
#define RNG_MODULE_NAME "hw_random"

#define RNG_MISCDEV_MINOR       183 /* official */

/* Changed at init time, in the non-modular case, and at module load
 * time, in the module case.  Presumably, the module subsystem
 * protects against a module being loaded twice at the same time.
 */
static int random_fd = -1;
static DECLARE_WAIT_QUEUE_HEAD(host_read_wait);

static int rng_dev_open (struct inode *inode, struct file *filp)
{
    /* enforce read-only access to this chrdev */
    if ((filp->f_mode & FMODE_READ) == 0)
        return -EINVAL;
    if ((filp->f_mode & FMODE_WRITE) != 0)
        return -EINVAL;

    return 0;
}

static atomic_t host_sleep_count = ATOMIC_INIT(0);

static ssize_t rng_dev_read (struct file *filp, char __user *buf, size_t size,
                 loff_t *offp)
{
    u32 data;
    int n, ret = 0, have_data;

    while (size) {
        n = os_read_file(random_fd, &data, sizeof(data));
        if (n > 0) {
            have_data = n;
            while (have_data && size) {
                if (put_user((u8) data, buf++)) {
                    ret = ret ? : -EFAULT;
                    break;
                }
                size--;
                ret++;
                have_data--;
                data >>= 8;
            }
        }
        else if (n == -EAGAIN) {
            DECLARE_WAITQUEUE(wait, current);

            if (filp->f_flags & O_NONBLOCK)
                return ret ? : -EAGAIN;

            atomic_inc(&host_sleep_count);
            reactivate_fd(random_fd, RANDOM_IRQ);
            add_sigio_fd(random_fd);

            add_wait_queue(&host_read_wait, &wait);
            set_task_state(current, TASK_INTERRUPTIBLE);

            schedule();
            set_task_state(current, TASK_RUNNING);
            remove_wait_queue(&host_read_wait, &wait);

            if (atomic_dec_and_test(&host_sleep_count)) {
                ignore_sigio_fd(random_fd);
                deactivate_fd(random_fd, RANDOM_IRQ);
            }
        }
        else
            return n;

        if (signal_pending (current))
            return ret ? : -ERESTARTSYS;
    }
    return ret;
}

static const struct file_operations rng_chrdev_ops = {
    .owner      = THIS_MODULE,
    .open       = rng_dev_open,
    .read       = rng_dev_read,
    .llseek     = noop_llseek,
};

/* rng_init shouldn't be called more than once at boot time */
static struct miscdevice rng_miscdev = {
    RNG_MISCDEV_MINOR,
    RNG_MODULE_NAME,
    &rng_chrdev_ops,
};

static irqreturn_t random_interrupt(int irq, void *data)
{
    wake_up(&host_read_wait);

    return IRQ_HANDLED;
}

/*
 * rng_init - initialize RNG module
 */
static int __init rng_init (void)
{
    int err;

    err = os_open_file("/dev/random", of_read(OPENFLAGS()), 0);
    if (err < 0)
        goto out;

    random_fd = err;

    err = um_request_irq(RANDOM_IRQ, random_fd, IRQ_READ, random_interrupt,
                 0, "random", NULL);
    if (err)
        goto err_out_cleanup_hw;

    sigio_broken(random_fd, 1);

    err = misc_register (&rng_miscdev);
    if (err) {
        printk (KERN_ERR RNG_MODULE_NAME ": misc device register "
            "failed\n");
        goto err_out_cleanup_hw;
    }
out:
    return err;

err_out_cleanup_hw:
    os_close_file(random_fd);
    random_fd = -1;
    goto out;
}

/*
 * rng_cleanup - shutdown RNG module
 */
static void __exit rng_cleanup (void)
{
    os_close_file(random_fd);
    misc_deregister (&rng_miscdev);
}

module_init (rng_init);
module_exit (rng_cleanup);

MODULE_DESCRIPTION("UML Host Random Number Generator (RNG) driver");
MODULE_LICENSE("GPL");