remarkable-linux/include/linux/kfifo.h

/*
 * A simple kernel FIFO implementation.
 *
 * Copyright (C) 2004 Stelian Pop <stelian@popies.net>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 */
#ifndef _LINUX_KFIFO_H
#define _LINUX_KFIFO_H

#ifdef __KERNEL__

#include <linux/kernel.h>
#include <linux/spinlock.h>

struct kfifo {
	unsigned char *buffer;	/* the buffer holding the data */
	unsigned int size;	/* the size of the allocated buffer */
	unsigned int in;	/* data is added at offset (in % size) */
	unsigned int out;	/* data is extracted from off. (out % size) */
	spinlock_t *lock;	/* protects concurrent modifications */
};

extern struct kfifo *kfifo_init(unsigned char *buffer, unsigned int size,
				gfp_t gfp_mask, spinlock_t *lock);
extern struct kfifo *kfifo_alloc(unsigned int size, gfp_t gfp_mask,
				 spinlock_t *lock);
extern void kfifo_free(struct kfifo *fifo);
extern unsigned int __kfifo_put(struct kfifo *fifo,
				unsigned char *buffer, unsigned int len);
extern unsigned int __kfifo_get(struct kfifo *fifo,
				unsigned char *buffer, unsigned int len);

/**
 * __kfifo_reset - removes the entire FIFO contents, no locking version
 * @fifo: the fifo to be emptied.
 */
static inline void __kfifo_reset(struct kfifo *fifo)
{
	fifo->in = fifo->out = 0;
}

/**
 * kfifo_reset - removes the entire FIFO contents
 * @fifo: the fifo to be emptied.
 */
static inline void kfifo_reset(struct kfifo *fifo)
{
	unsigned long flags;

	spin_lock_irqsave(fifo->lock, flags);

	__kfifo_reset(fifo);

	spin_unlock_irqrestore(fifo->lock, flags);
}

/**
 * kfifo_put - puts some data into the FIFO
 * @fifo: the fifo to be used.
 * @buffer: the data to be added.
 * @len: the length of the data to be added.
 *
 * This function copies at most 'len' bytes from the 'buffer' into
 * the FIFO depending on the free space, and returns the number of
 * bytes copied.
 */
static inline unsigned int kfifo_put(struct kfifo *fifo,
				     unsigned char *buffer, unsigned int len)
{
	unsigned long flags;
	unsigned int ret;

	spin_lock_irqsave(fifo->lock, flags);

	ret = __kfifo_put(fifo, buffer, len);

	spin_unlock_irqrestore(fifo->lock, flags);

	return ret;
}

/**
 * kfifo_get - gets some data from the FIFO
 * @fifo: the fifo to be used.
 * @buffer: where the data must be copied.
 * @len: the size of the destination buffer.
 *
 * This function copies at most 'len' bytes from the FIFO into the
 * 'buffer' and returns the number of copied bytes.
 */
static inline unsigned int kfifo_get(struct kfifo *fifo,
				     unsigned char *buffer, unsigned int len)
{
	unsigned long flags;
	unsigned int ret;

	spin_lock_irqsave(fifo->lock, flags);

	ret = __kfifo_get(fifo, buffer, len);

	/*
	 * optimization: if the FIFO is empty, set the indices to 0
	 * so we don't wrap the next time
	 */
	if (fifo->in == fifo->out)
		fifo->in = fifo->out = 0;

	spin_unlock_irqrestore(fifo->lock, flags);

	return ret;
}

/**
 * __kfifo_len - returns the number of bytes available in the FIFO, no locking version
 * @fifo: the fifo to be used.
 */
static inline unsigned int __kfifo_len(struct kfifo *fifo)
{
	return fifo->in - fifo->out;
}

/**
 * kfifo_len - returns the number of bytes available in the FIFO
 * @fifo: the fifo to be used.
 */
static inline unsigned int kfifo_len(struct kfifo *fifo)
{
	unsigned long flags;
	unsigned int ret;

	spin_lock_irqsave(fifo->lock, flags);

	ret = __kfifo_len(fifo);

	spin_unlock_irqrestore(fifo->lock, flags);

	return ret;
}

#else
#warning "don't include kernel headers in userspace"
#endif /* __KERNEL__ */
#endif