内核ring buffer -- kfifo

目前kernel的kfifo根据版本有两种形式， 早期的函数形式和现在的宏定义形式

1. 早期的（linux-3.0.56/kernel/kfifo.c）

感兴趣读者可以自己看， 源码如下：

/*
 * A generic kernel FIFO implementation
 *
 * Copyright (C) 2009/2010 Stefani Seibold <stefani@seibold.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/log2.h>
#include <linux/uaccess.h>
#include <linux/kfifo.h>

/*
 * internal helper to calculate the unused elements in a fifo
 */
static inline unsigned int kfifo_unused(struct __kfifo *fifo)
{
    return (fifo->mask + 1) - (fifo->in - fifo->out);
}

int __kfifo_alloc(struct __kfifo *fifo, unsigned int size,
        size_t esize, gfp_t gfp_mask)
{
    /*
     * round down to the next power of 2, since our 'let the indices
     * wrap' technique works only in this case.
     */
    if (!is_power_of_2(size))
        size = rounddown_pow_of_two(size);

    fifo->in = 0;
    fifo->out = 0;
    fifo->esize = esize;

    if (size < 2) {
        fifo->data = NULL;
        fifo->mask = 0;
        return -EINVAL;
    }

    fifo->data = kmalloc(size * esize, gfp_mask);

    if (!fifo->data) {
        fifo->mask = 0;
        return -ENOMEM;
    }
    fifo->mask = size - 1;

    return 0;
}
EXPORT_SYMBOL(__kfifo_alloc);

void __kfifo_free(struct __kfifo *fifo)
{
    kfree(fifo->data);
    fifo->in = 0;
    fifo->out = 0;
    fifo->esize = 0;
    fifo->data = NULL;
    fifo->mask = 0;
}
EXPORT_SYMBOL(__kfifo_free);

int __kfifo_init(struct __kfifo *fifo, void *buffer,
        unsigned int size, size_t esize)
{
    size /= esize;

    if (!is_power_of_2(size))
        size = rounddown_pow_of_two(size);

    fifo->in = 0;
    fifo->out = 0;
    fifo->esize = esize;
    fifo->data = buffer;

    if (size < 2) {
        fifo->mask = 0;
        return -EINVAL;
    }
    fifo->mask = size - 1;

    return 0;
}
EXPORT_SYMBOL(__kfifo_init);

static void kfifo_copy_in(struct __kfifo *fifo, const void *src,
        unsigned int len, unsigned int off)
{
    unsigned int size = fifo->mask + 1;
    unsigned int esize = fifo->esize;
    unsigned int l;

    off &= fifo->mask;
    if (esize != 1) {
        off *= esize;
        size *= esize;
        len *= esize;
    }
    l = min(len, size - off);

    memcpy(fifo->data + off, src, l);
    memcpy(fifo->data, src + l, len - l);
    /*
     * make sure that the data in the fifo is up to date before
     * incrementing the fifo->in index counter
     */
    smp_wmb();
}

unsigned int __kfifo_in(struct __kfifo *fifo,
        const void *buf, unsigned int len)
{
    unsigned int l;

    l = kfifo_unused(fifo);
    if (len > l)
        len = l;

    kfifo_copy_in(fifo, buf, len, fifo->in);
    fifo->in += len;
    return len;
}
EXPORT_SYMBOL(__kfifo_in);

static void kfifo_copy_out(struct __kfifo *fifo, void *dst,
        unsigned int len, unsigned int off)
{
    unsigned int size = fifo->mask + 1;
    unsigned int esize = fifo->esize;
    unsigned int l;

    off &= fifo->mask;
    if (esize != 1) {
        off *= esize;
        size *= esize;
        len *= esize;
    }
    l = min(len, size - off);

    memcpy(dst, fifo->data + off, l);
    memcpy(dst + l, fifo->data, len - l);
    /*
     * make sure that the data is copied before
     * incrementing the fifo->out index counter
     */
    smp_wmb();
}

unsigned int __kfifo_out_peek(struct __kfifo *fifo,
        void *buf, unsigned int len)
{
    unsigned int l;

    l = fifo->in - fifo->out;
    if (len > l)
        len = l;

    kfifo_copy_out(fifo, buf, len, fifo->out);
    return len;
}
EXPORT_SYMBOL(__kfifo_out_peek);

unsigned int __kfifo_out(struct __kfifo *fifo,
        void *buf, unsigned int len)
{
    len = __kfifo_out_peek(fifo, buf, len);
    fifo->out += len;
    return len;
}
EXPORT_SYMBOL(__kfifo_out);

static unsigned long kfifo_copy_from_user(struct __kfifo *fifo,
    const void __user *from, unsigned int len, unsigned int off,
    unsigned int *copied)
{
    unsigned int size = fifo->mask + 1;
    unsigned int esize = fifo->esize;
    unsigned int l;
    unsigned long ret;

    off &= fifo->mask;
    if (esize != 1) {
        off *= esize;
        size *= esize;
        len *= esize;
    }
    l = min(len, size - off);

    ret = copy_from_user(fifo->data + off, from, l);
    if (unlikely(ret))
        ret = DIV_ROUND_UP(ret + len - l, esize);
    else {
        ret = copy_from_user(fifo->data, from + l, len - l);
        if (unlikely(ret))
            ret = DIV_ROUND_UP(ret, esize);
    }
    /*
     * make sure that the data in the fifo is up to date before
     * incrementing the fifo->in index counter
     */
    smp_wmb();
    *copied = len - ret;
    /* return the number of elements which are not copied */
    return ret;
}

int __kfifo_from_user(struct __kfifo *fifo, const void __user *from,
        unsigned long len, unsigned int *copied)
{
    unsigned int l;
    unsigned long ret;
    unsigned int esize = fifo->esize;
    int err;

    if (esize != 1)
        len /= esize;

    l = kfifo_unused(fifo);
    if (len > l)
        len = l;

    ret = kfifo_copy_from_user(fifo, from, len, fifo->in, copied);
    if (unlikely(ret)) {
        len -= ret;
        err = -EFAULT;
    } else
        err = 0;
    fifo->in += len;
    return err;
}
EXPORT_SYMBOL(__kfifo_from_user);

static unsigned long kfifo_copy_to_user(struct __kfifo *fifo, void __user *to,
        unsigned int len, unsigned int off, unsigned int *copied)
{
    unsigned int l;
    unsigned long ret;
    unsigned int size = fifo->mask + 1;
    unsigned int esize = fifo->esize;

    off &= fifo->mask;
    if (esize != 1) {
        off *= esize;
        size *= esize;
        len *= esize;
    }
    l = min(len, size - off);

    ret = copy_to_user(to, fifo->data + off, l);
    if (unlikely(ret))
        ret = DIV_ROUND_UP(ret + len - l, esize);
    else {
        ret = copy_to_user(to + l, fifo->data, len - l);
        if (unlikely(ret))
            ret = DIV_ROUND_UP(ret, esize);
    }
    /*
     * make sure that the data is copied before
     * incrementing the fifo->out index counter
     */
    smp_wmb();
    *copied = len - ret;
    /* return the number of elements which are not copied */
    return ret;
}

int __kfifo_to_user(struct __kfifo *fifo, void __user *to,
        unsigned long len, unsigned int *copied)
{
    unsigned int l;
    unsigned long ret;
    unsigned int esize = fifo->esize;
    int err;

    if (esize != 1)
        len /= esize;

    l = fifo->in - fifo->out;
    if (len > l)
        len = l;
    ret = kfifo_copy_to_user(fifo, to, len, fifo->out, copied);
    if (unlikely(ret)) {
        len -= ret;
        err = -EFAULT;
    } else
        err = 0;
    fifo->out += len;
    return err;
}
EXPORT_SYMBOL(__kfifo_to_user);

static int setup_sgl_buf(struct scatterlist *sgl, void *buf,
        int nents, unsigned int len)
{
    int n;
    unsigned int l;
    unsigned int off;
    struct page *page;

    if (!nents)
        return 0;

    if (!len)
        return 0;

    n = 0;
    page = virt_to_page(buf);
    off = offset_in_page(buf);
    l = 0;

    while (len >= l + PAGE_SIZE - off) {
        struct page *npage;

        l += PAGE_SIZE;
        buf += PAGE_SIZE;
        npage = virt_to_page(buf);
        if (page_to_phys(page) != page_to_phys(npage) - l) {
            sg_set_page(sgl, page, l - off, off);
            sgl = sg_next(sgl);
            if (++n == nents || sgl == NULL)
                return n;
            page = npage;
            len -= l - off;
            l = off = 0;
        }
    }
    sg_set_page(sgl, page, len, off);
    return n + 1;
}

static unsigned int setup_sgl(struct __kfifo *fifo, struct scatterlist *sgl,
        int nents, unsigned int len, unsigned int off)
{
    unsigned int size = fifo->mask + 1;
    unsigned int esize = fifo->esize;
    unsigned int l;
    unsigned int n;

    off &= fifo->mask;
    if (esize != 1) {
        off *= esize;
        size *= esize;
        len *= esize;
    }
    l = min(len, size - off);

    n = setup_sgl_buf(sgl, fifo->data + off, nents, l);
    n += setup_sgl_buf(sgl + n, fifo->data, nents - n, len - l);

    return n;
}

unsigned int __kfifo_dma_in_prepare(struct __kfifo *fifo,
        struct scatterlist *sgl, int nents, unsigned int len)
{
    unsigned int l;

    l = kfifo_unused(fifo);
    if (len > l)
        len = l;

    return setup_sgl(fifo, sgl, nents, len, fifo->in);
}
EXPORT_SYMBOL(__kfifo_dma_in_prepare);

unsigned int __kfifo_dma_out_prepare(struct __kfifo *fifo,
        struct scatterlist *sgl, int nents, unsigned int len)
{
    unsigned int l;

    l = fifo->in - fifo->out;
    if (len > l)
        len = l;

    return setup_sgl(fifo, sgl, nents, len, fifo->out);
}
EXPORT_SYMBOL(__kfifo_dma_out_prepare);

unsigned int __kfifo_max_r(unsigned int len, size_t recsize)
{
    unsigned int max = (1 << (recsize << 3)) - 1;

    if (len > max)
        return max;
    return len;
}

#define    __KFIFO_PEEK(data, out, mask) \
    ((data)[(out) & (mask)])
/*
 * __kfifo_peek_n internal helper function for determinate the length of
 * the next record in the fifo
 */
static unsigned int __kfifo_peek_n(struct __kfifo *fifo, size_t recsize)
{
    unsigned int l;
    unsigned int mask = fifo->mask;
    unsigned char *data = fifo->data;

    l = __KFIFO_PEEK(data, fifo->out, mask);

    if (--recsize)
        l |= __KFIFO_PEEK(data, fifo->out + 1, mask) << 8;

    return l;
}

#define    __KFIFO_POKE(data, in, mask, val) \
    ( \
    (data)[(in) & (mask)] = (unsigned char)(val) \
    )

/*
 * __kfifo_poke_n internal helper function for storeing the length of
 * the record into the fifo
 */
static void __kfifo_poke_n(struct __kfifo *fifo, unsigned int n, size_t recsize)
{
    unsigned int mask = fifo->mask;
    unsigned char *data = fifo->data;

    __KFIFO_POKE(data, fifo->in, mask, n);

    if (recsize > 1)
        __KFIFO_POKE(data, fifo->in + 1, mask, n >> 8);
}

unsigned int __kfifo_len_r(struct __kfifo *fifo, size_t recsize)
{
    return __kfifo_peek_n(fifo, recsize);
}
EXPORT_SYMBOL(__kfifo_len_r);

unsigned int __kfifo_in_r(struct __kfifo *fifo, const void *buf,
        unsigned int len, size_t recsize)
{
    if (len + recsize > kfifo_unused(fifo))
        return 0;

    __kfifo_poke_n(fifo, len, recsize);

    kfifo_copy_in(fifo, buf, len, fifo->in + recsize);
    fifo->in += len + recsize;
    return len;
}
EXPORT_SYMBOL(__kfifo_in_r);

static unsigned int kfifo_out_copy_r(struct __kfifo *fifo,
    void *buf, unsigned int len, size_t recsize, unsigned int *n)
{
    *n = __kfifo_peek_n(fifo, recsize);

    if (len > *n)
        len = *n;

    kfifo_copy_out(fifo, buf, len, fifo->out + recsize);
    return len;
}

unsigned int __kfifo_out_peek_r(struct __kfifo *fifo, void *buf,
        unsigned int len, size_t recsize)
{
    unsigned int n;

    if (fifo->in == fifo->out)
        return 0;

    return kfifo_out_copy_r(fifo, buf, len, recsize, &n);
}
EXPORT_SYMBOL(__kfifo_out_peek_r);

unsigned int __kfifo_out_r(struct __kfifo *fifo, void *buf,
        unsigned int len, size_t recsize)
{
    unsigned int n;

    if (fifo->in == fifo->out)
        return 0;

    len = kfifo_out_copy_r(fifo, buf, len, recsize, &n);
    fifo->out += n + recsize;
    return len;
}
EXPORT_SYMBOL(__kfifo_out_r);

void __kfifo_skip_r(struct __kfifo *fifo, size_t recsize)
{
    unsigned int n;

    n = __kfifo_peek_n(fifo, recsize);
    fifo->out += n + recsize;
}
EXPORT_SYMBOL(__kfifo_skip_r);

int __kfifo_from_user_r(struct __kfifo *fifo, const void __user *from,
    unsigned long len, unsigned int *copied, size_t recsize)
{
    unsigned long ret;

    len = __kfifo_max_r(len, recsize);

    if (len + recsize > kfifo_unused(fifo)) {
        *copied = 0;
        return 0;
    }

    __kfifo_poke_n(fifo, len, recsize);

    ret = kfifo_copy_from_user(fifo, from, len, fifo->in + recsize, copied);
    if (unlikely(ret)) {
        *copied = 0;
        return -EFAULT;
    }
    fifo->in += len + recsize;
    return 0;
}
EXPORT_SYMBOL(__kfifo_from_user_r);

int __kfifo_to_user_r(struct __kfifo *fifo, void __user *to,
    unsigned long len, unsigned int *copied, size_t recsize)
{
    unsigned long ret;
    unsigned int n;

    if (fifo->in == fifo->out) {
        *copied = 0;
        return 0;
    }

    n = __kfifo_peek_n(fifo, recsize);
    if (len > n)
        len = n;

    ret = kfifo_copy_to_user(fifo, to, len, fifo->out + recsize, copied);
    if (unlikely(ret)) {
        *copied = 0;
        return -EFAULT;
    }
    fifo->out += n + recsize;
    return 0;
}
EXPORT_SYMBOL(__kfifo_to_user_r);

unsigned int __kfifo_dma_in_prepare_r(struct __kfifo *fifo,
    struct scatterlist *sgl, int nents, unsigned int len, size_t recsize)
{
    if (!nents)
        BUG();

    len = __kfifo_max_r(len, recsize);

    if (len + recsize > kfifo_unused(fifo))
        return 0;

    return setup_sgl(fifo, sgl, nents, len, fifo->in + recsize);
}
EXPORT_SYMBOL(__kfifo_dma_in_prepare_r);

void __kfifo_dma_in_finish_r(struct __kfifo *fifo,
    unsigned int len, size_t recsize)
{
    len = __kfifo_max_r(len, recsize);
    __kfifo_poke_n(fifo, len, recsize);
    fifo->in += len + recsize;
}
EXPORT_SYMBOL(__kfifo_dma_in_finish_r);

unsigned int __kfifo_dma_out_prepare_r(struct __kfifo *fifo,
    struct scatterlist *sgl, int nents, unsigned int len, size_t recsize)
{
    if (!nents)
        BUG();

    len = __kfifo_max_r(len, recsize);

    if (len + recsize > fifo->in - fifo->out)
        return 0;

    return setup_sgl(fifo, sgl, nents, len, fifo->out + recsize);
}
EXPORT_SYMBOL(__kfifo_dma_out_prepare_r);

void __kfifo_dma_out_finish_r(struct __kfifo *fifo, size_t recsize)
{
    unsigned int len;

    len = __kfifo_peek_n(fifo, recsize);
    fifo->out += len + recsize;
}
EXPORT_SYMBOL(__kfifo_dma_out_finish_r);

linux-3.0.56/kernel/kfifo.c