[PATCH 1/5] drivers: add simple hw_random implementation

[Sascha Hauer]

On Fri, Feb 26, 2016 at 01:04:43PM +0100, Steffen Trumtrar wrote:
> Add a simple hw_random implementation based on code from
> Linux v4.5-rc5.
> 
> All the entropypool initialization stuff is left out and
> the obsolete data_read/data_present calls are omitted.
> 
> Signed-off-by: Steffen Trumtrar <s.trumtrar at pengutronix.de>
> ---
> +#include <common.h>
> +#include <linux/hw_random.h>
> +
> +static LIST_HEAD(hwrngs);
> +
> +#define RNG_BUFFER_SIZE		32
> +
> +int hwrng_get_data(struct hwrng *rng, u8 *buffer, size_t size, int wait)
> +{
> +	if (rng->read)
> +		return rng->read(rng, buffer, size, wait);

When rng->read is NULL you already fail in the registration, no need to
check here.

> +
> +	return 0;
> +}
> +
> +static int hwrng_init(struct hwrng *rng)
> +{
> +	int ret = 0;
> +
> +	if (rng->init)
> +		ret = rng->init(rng);
> +
> +	list_add_tail(&rng->list, &hwrngs);

When rng->init fails you probably don't want to add it to the list.

> +
> +	return ret;
> +}
> +
> +static ssize_t rng_dev_read(struct cdev *cdev, void *buf, size_t size,
> +			    loff_t offset, unsigned long flags)
> +{
> +	struct hwrng *rng = container_of(cdev, struct hwrng, cdev);
> +	ssize_t cur = 0;
> +	int err = 0;
> +	int len;
> +	size_t count = size;
> +
> +	memset(buf, 0, size);
> +
> +	while (count) {

You can initialize a variable with the minimum of count and
RNG_BUFFER_SIZE here,

> +		len = hwrng_get_data(rng, rng->buf, RNG_BUFFER_SIZE, true);

Use it here instead of RNG_BUFFER_SIZE

> +		if (len < 0) {
> +			err = len;
> +			break;
> +		}
> +
> +		if (len > count)
> +			len = count;

and drop this check.

> +
> +		memcpy(buf + cur, rng->buf, len);
> +
> +		count -= len;
> +		cur += len;
> +	}
> +
> +	return cur ? : err;

When you get an error in the second loop iteration then cur is true and
you return it instead of the error. Is that what you want?

> +}
> +
> +
> +static struct file_operations rng_chrdev_ops = {
> +	.read  = rng_dev_read,
> +	.lseek = dev_lseek_default,
> +};
> +
> +static int hwrng_register_cdev(struct hwrng *rng)
> +{
> +	rng->cdev.name = "hwrng";
> +	rng->cdev.flags = DEVFS_IS_CHARACTER_DEV;
> +	rng->cdev.ops = &rng_chrdev_ops;
> +	rng->cdev.dev = rng->dev;
> +
> +	return devfs_create(&rng->cdev);
> +}
> +
> +struct hwrng *hwrng_get_first(void)
> +{
> +	if (!list_empty(&hwrngs))
> +		return list_first_entry(&hwrngs, struct hwrng, list);
> +	else
> +		return ERR_PTR(-ENODEV);

Please use positive logic, it's usually easier to read.

> +}
> +
> +int hwrng_register(struct device_d *dev, struct hwrng *rng)
> +{
> +	int err;
> +
> +	if (rng->name == NULL || rng->read == NULL)
> +		return -EINVAL;
> +
> +	rng->buf = xzalloc(RNG_BUFFER_SIZE);

Please make sure you do not loose memory in infrastructure code.

> +
> +	err = hwrng_init(rng);
> +	if (err)
> +		return err;
> +
> +	rng->dev = dev;
> +
> +	err = hwrng_register_cdev(rng);
> +
> +	return err;
> +}
> +        of the GNU General Public License, incorporated herein by reference.
> +
> + */
> +
> +#ifndef LINUX_HWRANDOM_H_
> +#define LINUX_HWRANDOM_H_
> +
> +#include <linux/list.h>
> +
> +/**
> + * struct hwrng - Hardware Random Number Generator driver
> + * @name:		Unique RNG name.
> + * @init:		Initialization callback (can be NULL).
> + * @read:		New API. drivers can fill up to max bytes of data
> + *			into the buffer. The buffer is aligned for any type.
> + * @priv:		Private data, for use by the RNG driver.
> + */
> +struct hwrng {
> +	const char *name;
> +	int (*init)(struct hwrng *rng);
> +	int (*read)(struct hwrng *rng, void *data, size_t max, bool wait);
> +	unsigned long priv;

This is unused, no?

Sascha

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