/*
 * 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.
 *
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/err.h>
#include <linux/kfifo.h>
#include <linux/log2.h>

/**
 * kfifo_init - allocates a new FIFO using a preallocated buffer
 * @buffer: the preallocated buffer to be used.
 * @size: the size of the internal buffer, this have to be a power of 2.
 * @gfp_mask: get_free_pages mask, passed to kmalloc()
 * @lock: the lock to be used to protect the fifo buffer
 *
 * Do NOT pass the kfifo to kfifo_free() after use! Simply free the
 * &struct kfifo with kfree().
 */
struct kfifo *kfifo_init(unsigned char *buffer, unsigned int size,
                         gfp_t gfp_mask, spinlock_t *lock)
{
        struct kfifo *fifo;

        /* size must be a power of 2 */
        BUG_ON(!is_power_of_2(size));

        fifo = kmalloc(sizeof(struct kfifo), gfp_mask);
        if (!fifo)
                return ERR_PTR(-ENOMEM);

        fifo->buffer = buffer;
        fifo->size = size;
        fifo->in = fifo->out = 0;
        fifo->lock = lock;

        return fifo;
}
EXPORT_SYMBOL(kfifo_init);

/**
 * kfifo_alloc - allocates a new FIFO and its internal buffer
 * @size: the size of the internal buffer to be allocated.
 * @gfp_mask: get_free_pages mask, passed to kmalloc()
 * @lock: the lock to be used to protect the fifo buffer
 *
 * The size will be rounded-up to a power of 2.
 */
struct kfifo *kfifo_alloc(unsigned int size, gfp_t gfp_mask, spinlock_t *lock)
{
        unsigned char *buffer;
        struct kfifo *ret;

        /*
         * round up to the next power of 2, since our 'let the indices
         * wrap' technique works only in this case.
         */
        if (!is_power_of_2(size)) {
                BUG_ON(size > 0x80000000);
                size = roundup_pow_of_two(size);
        }

        buffer = kmalloc(size, gfp_mask);
        if (!buffer)
                return ERR_PTR(-ENOMEM);

        ret = kfifo_init(buffer, size, gfp_mask, lock);

        if (IS_ERR(ret))
                kfree(buffer);

        return ret;
}
EXPORT_SYMBOL(kfifo_alloc);

/**
 * kfifo_free - frees the FIFO
 * @fifo: the fifo to be freed.
 */
void kfifo_free(struct kfifo *fifo)
{
        kfree(fifo->buffer);
        kfree(fifo);
}
EXPORT_SYMBOL(kfifo_free);

/**
 * __kfifo_put - puts some data into the FIFO, no locking version
 * @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.
 *
 * Note that with only one concurrent reader and one concurrent
 * writer, you don't need extra locking to use these functions.
 */
unsigned int __kfifo_put(struct kfifo *fifo,
                        const unsigned char *buffer, unsigned int len)
{
        unsigned int l;

        len = min(len, fifo->size - fifo->in + fifo->out);

        /*
         * Ensure that we sample the fifo->out index -before- we
         * start putting bytes into the kfifo.
         */

        smp_mb();

        /* first put the data starting from fifo->in to buffer end */
        l = min(len, fifo->size - (fifo->in & (fifo->size - 1)));
        memcpy(fifo->buffer + (fifo->in & (fifo->size - 1)), buffer, l);

        /* then put the rest (if any) at the beginning of the buffer */
        memcpy(fifo->buffer, buffer + l, len - l);

        /*
         * Ensure that we add the bytes to the kfifo -before-
         * we update the fifo->in index.
         */

        smp_wmb();

        fifo->in += len;

        return len;
}
EXPORT_SYMBOL(__kfifo_put);

/**
 * __kfifo_get - gets some data from the FIFO, no locking version
 * @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.
 *
 * Note that with only one concurrent reader and one concurrent
 * writer, you don't need extra locking to use these functions.
 */
unsigned int __kfifo_get(struct kfifo *fifo,
                         unsigned char *buffer, unsigned int len)
{
        unsigned int l;

        len = min(len, fifo->in - fifo->out);

        /*
         * Ensure that we sample the fifo->in index -before- we
         * start removing bytes from the kfifo.
         */

        smp_rmb();

        /* first get the data from fifo->out until the end of the buffer */
        l = min(len, fifo->size - (fifo->out & (fifo->size - 1)));
        memcpy(buffer, fifo->buffer + (fifo->out & (fifo->size - 1)), l);

        /* then get the rest (if any) from the beginning of the buffer */
        memcpy(buffer + l, fifo->buffer, len - l);

        /*
         * Ensure that we remove the bytes from the kfifo -before-
         * we update the fifo->out index.
         */

        smp_mb();

        fifo->out += len;

        return len;
}
EXPORT_SYMBOL(__kfifo_get);