1. 根目录:
2. drivers
3. staging
4. iio
5. kfifo_buf.c

#include <linux/slab.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/device.h>
#include <linux/workqueue.h>
#include <linux/kfifo.h>
#include <linux/mutex.h>

#include "kfifo_buf.h"

static inline int __iio_allocate_kfifo(struct iio_kfifo *buf,
				int bytes_per_datum, int length)
{
	if ((length == 0) || (bytes_per_datum == 0))
		return -EINVAL;

	__iio_update_ring_buffer(&buf->ring, bytes_per_datum, length);
	return kfifo_alloc(&buf->kf, bytes_per_datum*length, GFP_KERNEL);
}

int iio_request_update_kfifo(struct iio_ring_buffer *r)
{
	int ret = 0;
	struct iio_kfifo *buf = iio_to_kfifo(r);

	mutex_lock(&buf->use_lock);
	if (!buf->update_needed)
		goto error_ret;
	if (buf->use_count) {
		ret = -EAGAIN;
		goto error_ret;
	}
	kfifo_free(&buf->kf);
	ret = __iio_allocate_kfifo(buf, buf->ring.bytes_per_datum,
				buf->ring.length);
error_ret:
	mutex_unlock(&buf->use_lock);
	return ret;
}
EXPORT_SYMBOL(iio_request_update_kfifo);

void iio_mark_kfifo_in_use(struct iio_ring_buffer *r)
{
	struct iio_kfifo *buf = iio_to_kfifo(r);
	mutex_lock(&buf->use_lock);
	buf->use_count++;
	mutex_unlock(&buf->use_lock);
}
EXPORT_SYMBOL(iio_mark_kfifo_in_use);

void iio_unmark_kfifo_in_use(struct iio_ring_buffer *r)
{
	struct iio_kfifo *buf = iio_to_kfifo(r);
	mutex_lock(&buf->use_lock);
	buf->use_count--;
	mutex_unlock(&buf->use_lock);
}
EXPORT_SYMBOL(iio_unmark_kfifo_in_use);

int iio_get_length_kfifo(struct iio_ring_buffer *r)
{
	return r->length;
}
EXPORT_SYMBOL(iio_get_length_kfifo);

static inline void __iio_init_kfifo(struct iio_kfifo *kf)
{
	mutex_init(&kf->use_lock);
}

static IIO_RING_ENABLE_ATTR;
static IIO_RING_BYTES_PER_DATUM_ATTR;
static IIO_RING_LENGTH_ATTR;

static struct attribute *iio_kfifo_attributes[] = {
	&dev_attr_length.attr,
	&dev_attr_bytes_per_datum.attr,
	&dev_attr_enable.attr,
	NULL,
};

static struct attribute_group iio_kfifo_attribute_group = {
	.attrs = iio_kfifo_attributes,
};

static const struct attribute_group *iio_kfifo_attribute_groups[] = {
	&iio_kfifo_attribute_group,
	NULL
};

static void iio_kfifo_release(struct device *dev)
{
	struct iio_ring_buffer *r = to_iio_ring_buffer(dev);
	struct iio_kfifo *kf = iio_to_kfifo(r);
	kfifo_free(&kf->kf);
	kfree(kf);
}

static struct device_type iio_kfifo_type = {
	.release = iio_kfifo_release,
	.groups = iio_kfifo_attribute_groups,
};

struct iio_ring_buffer *iio_kfifo_allocate(struct iio_dev *indio_dev)
{
	struct iio_kfifo *kf;

	kf = kzalloc(sizeof *kf, GFP_KERNEL);
	if (!kf)
		return NULL;
	iio_ring_buffer_init(&kf->ring, indio_dev);
	__iio_init_kfifo(kf);
	kf->ring.dev.type = &iio_kfifo_type;
	device_initialize(&kf->ring.dev);
	kf->ring.dev.parent = &indio_dev->dev;
	kf->ring.dev.bus = &iio_bus_type;
	dev_set_drvdata(&kf->ring.dev, (void *)&(kf->ring));

	return &kf->ring;
}
EXPORT_SYMBOL(iio_kfifo_allocate);

int iio_get_bytes_per_datum_kfifo(struct iio_ring_buffer *r)
{
	return r->bytes_per_datum;
}
EXPORT_SYMBOL(iio_get_bytes_per_datum_kfifo);

int iio_set_bytes_per_datum_kfifo(struct iio_ring_buffer *r, size_t bpd)
{
	if (r->bytes_per_datum != bpd) {
		r->bytes_per_datum = bpd;
		if (r->access.mark_param_change)
			r->access.mark_param_change(r);
	}
	return 0;
}
EXPORT_SYMBOL(iio_set_bytes_per_datum_kfifo);

int iio_mark_update_needed_kfifo(struct iio_ring_buffer *r)
{
	struct iio_kfifo *kf = iio_to_kfifo(r);
	kf->update_needed = true;
	return 0;
}
EXPORT_SYMBOL(iio_mark_update_needed_kfifo);

int iio_set_length_kfifo(struct iio_ring_buffer *r, int length)
{
	if (r->length != length) {
		r->length = length;
		if (r->access.mark_param_change)
			r->access.mark_param_change(r);
	}
	return 0;
}
EXPORT_SYMBOL(iio_set_length_kfifo);

void iio_kfifo_free(struct iio_ring_buffer *r)
{
	if (r)
		iio_put_ring_buffer(r);
}
EXPORT_SYMBOL(iio_kfifo_free);

int iio_store_to_kfifo(struct iio_ring_buffer *r, u8 *data, s64 timestamp)
{
	int ret;
	struct iio_kfifo *kf = iio_to_kfifo(r);
	u8 *datal = kmalloc(r->bytes_per_datum, GFP_KERNEL);
	memcpy(datal, data, r->bytes_per_datum - sizeof(timestamp));
	memcpy(datal + r->bytes_per_datum - sizeof(timestamp),
		&timestamp, sizeof(timestamp));
	ret = kfifo_in(&kf->kf, data, r->bytes_per_datum);
	if (ret != r->bytes_per_datum) {
		kfree(datal);
		return -EBUSY;
	}
	kfree(datal);
	return 0;
}
EXPORT_SYMBOL(iio_store_to_kfifo);

int iio_rip_kfifo(struct iio_ring_buffer *r,
		size_t count, char __user *buf, int *deadoffset)
{
	int ret, copied;
	struct iio_kfifo *kf = iio_to_kfifo(r);

	*deadoffset = 0;
	ret = kfifo_to_user(&kf->kf, buf, r->bytes_per_datum*count, &copied);

	return copied;
}
EXPORT_SYMBOL(iio_rip_kfifo);
MODULE_LICENSE("GPL");