kernel-fxtec-pro1x/arch/um/drivers/random.c
Jeff Dike 5d33e4d7fd uml: random driver fixes
The random driver would essentially hang if the host's /dev/random returned
-EAGAIN.  There was a test of need_resched followed by a schedule inside the
loop, but that didn't help and it's the wrong way to work anyway.

The right way is to ask for an interrupt when there is input available from
the host and handle it then rather than polling.

Now, when the host's /dev/random returns -EAGAIN, the driver asks for a wakeup
when there's randomness available again and sleeps.  The interrupt routine
just wakes up whatever processes are sleeping on host_read_wait.

There is an atomic_t, host_sleep_count, which counts the number of processes
waiting for randomness.  When this reaches zero, the interrupt is disabled.

An added complication is that async I/O notification was only recently added
to /dev/random (by me), so essentially all hosts will lack it.  So, we use the
sigio workaround here, which is to have a separate thread poll on the
descriptor and send an interrupt when there is input on it.  This mechanism is
activated when a process gets -EAGAIN (activating this multiple times is
harmless, if a bit wasteful) and deactivated by the last process still
waiting.

The module name was changed from "random" to "hw_random" in order for udev to
recognize it.

The sigio workaround needed some changes.  sigio_broken was added for cases
when we know that async notification doesn't work.  This is now called from
maybe_sigio_broken, which deals with pts devices.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-05-13 08:02:22 -07:00

165 lines
4.1 KiB
C

/* Copyright (C) 2005 Jeff Dike <jdike@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)
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");