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random.c

/* 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/smp_lock.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)
{
      cycle_kernel_lock();

      /* 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,
};

/* 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,
                       IRQF_DISABLED | IRQF_SAMPLE_RANDOM, "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");

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