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);

我自己参考后修改的：

/* referrence linux kfifo.c
 */

#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include "fifo.h"

#define min(x, y)    ((x) < (y) ? (x) : (y))
#define smp_wmb()    __asm__ __volatile__("": : :"memory")
#define is_power_of_2(x) ((x) != 0 && (((x) & ((x) - 1)) == 0))


static unsigned int roundup_pow_of_two(unsigned int x)
{
    int position = 0;
    int i;

    for (i = (x-1); i != 0; ++position)
        i >>= 1;

    return 1UL << position;
}

int kfifo_alloc(struct kfifo *fifo, unsigned int size)
{
    fifo->in = 0;
    fifo->out = 0;

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

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

    fifo->data = malloc(size);

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

    return 0;
}

void kfifo_free(struct kfifo *fifo)
{
    free(fifo->data);
    fifo->data = NULL;
    fifo->in = 0;
    fifo->out = 0;
    fifo->mask = 0;
}

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 l;

    /* that is why request size is power of two, instead of off %= fifo->size */
    off &= fifo->mask;
    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 = (fifo->mask + 1) - (fifo->in - fifo->out);
    if (len > l)
        len = l;

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

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

    off &= fifo->mask;
    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(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);
    fifo->out += len;
    return len;
}

　　

　　上面in out函数故意不加锁， 由调用者根据情况自己加， 而不是一刀切在这里加影响性能， 头文件：

#ifndef __VEDIC_FIFO_H__
#define __VEDIC_FIFO_H__

struct kfifo {
    unsigned int    in;
    unsigned int    out;
    unsigned int    mask;
    void        *data;
};

#define kfifo_size(fifo)    ((fifo)->kfifo.mask + 1)

int kfifo_alloc(struct kfifo *fifo, unsigned int size);

void kfifo_free(struct kfifo *fifo);

unsigned int kfifo_in(struct kfifo *fifo, const void *buf, unsigned int len);

unsigned int kfifo_out(struct kfifo *fifo, void *buf, unsigned int len);


#endif

　　

　　测试代码和结果：

#include <stdio.h>
#include "fifo.h"

unsigned char buf[300]={0};

void main()
{
    struct kfifo fifo;

    kfifo_alloc(&fifo, 255);
    printf("in counter %u
", kfifo_in(&fifo, buf, 20));
    printf("out counter %u
", kfifo_out(&fifo, buf, 10));    
}

$ gcc -c fifo.c
$ gcc -c main.c
$ gcc fifo.o main.o -o main.bin
$ ./main.bin 
in counter 20
out counter 10

　　关于in累加溢出的问题， 由于计算机存储是补码形式， 所以在一个ring buffer size下 （in - out） 还是正确的， 看测试case：

#include <stdio.h>

int main()
{
        unsigned char in=0, out=0, del;

        in = 250;
        out = 200;
        printf("1 in - out = %d
", in-out);

        in += 30;
        del = in - out;
        printf("2 in = %d,  del = %d
", in, del);
        printf("3 in - out = %d
", in-out);

        /* enlarge */
        in = 250;
        out = 200;
        in += 500;
        del = in - out;
        printf("4 in = %d,  del = %d
", in, del);

        /* limit */
        in = 250;
        out = 200;
        in += 255 - (in-out); // unsigned char max num = 255, not 256
        del = in - out;
        printf("5 in = %d,  del = %d
", in, del);

}

$ ./a.out 
1 in - out = 50
2 in = 24,  del = 80
3 in - out = -176
4 in = 238,  del = 38
5 in = 199,  del = 255

2. 现在的（只有头文件linux-3.10.65/include/linux/kfifo.h）

/*
 * 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.
 *
 */

#ifndef _LINUX_KFIFO_H
#define _LINUX_KFIFO_H

/*
 * How to porting drivers to the new generic FIFO API:
 *
 * - Modify the declaration of the "struct kfifo *" object into a
 *   in-place "struct kfifo" object
 * - Init the in-place object with kfifo_alloc() or kfifo_init()
 *   Note: The address of the in-place "struct kfifo" object must be
 *   passed as the first argument to this functions
 * - Replace the use of __kfifo_put into kfifo_in and __kfifo_get
 *   into kfifo_out
 * - Replace the use of kfifo_put into kfifo_in_spinlocked and kfifo_get
 *   into kfifo_out_spinlocked
 *   Note: the spinlock pointer formerly passed to kfifo_init/kfifo_alloc
 *   must be passed now to the kfifo_in_spinlocked and kfifo_out_spinlocked
 *   as the last parameter
 * - The formerly __kfifo_* functions are renamed into kfifo_*
 */

/*
 * Note about locking : There is no locking required until only * one reader
 * and one writer is using the fifo and no kfifo_reset() will be * called
 *  kfifo_reset_out() can be safely used, until it will be only called
 * in the reader thread.
 *  For multiple writer and one reader there is only a need to lock the writer.
 * And vice versa for only one writer and multiple reader there is only a need
 * to lock the reader.
 */

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

struct __kfifo {
    unsigned int    in;
    unsigned int    out;
    unsigned int    mask;
    unsigned int    esize;
    void        *data;
};

#define __STRUCT_KFIFO_COMMON(datatype, recsize, ptrtype) 
    union { 
        struct __kfifo    kfifo; 
        datatype    *type; 
        char        (*rectype)[recsize]; 
        ptrtype        *ptr; 
        const ptrtype    *ptr_const; 
    }

#define __STRUCT_KFIFO(type, size, recsize, ptrtype) 
{ 
    __STRUCT_KFIFO_COMMON(type, recsize, ptrtype); 
    type        buf[((size < 2) || (size & (size - 1))) ? -1 : size]; 
}

#define STRUCT_KFIFO(type, size) 
    struct __STRUCT_KFIFO(type, size, 0, type)

#define __STRUCT_KFIFO_PTR(type, recsize, ptrtype) 
{ 
    __STRUCT_KFIFO_COMMON(type, recsize, ptrtype); 
    type        buf[0]; 
}

#define STRUCT_KFIFO_PTR(type) 
    struct __STRUCT_KFIFO_PTR(type, 0, type)

/*
 * define compatibility "struct kfifo" for dynamic allocated fifos
 */
struct kfifo __STRUCT_KFIFO_PTR(unsigned char, 0, void);

#define STRUCT_KFIFO_REC_1(size) 
    struct __STRUCT_KFIFO(unsigned char, size, 1, void)

#define STRUCT_KFIFO_REC_2(size) 
    struct __STRUCT_KFIFO(unsigned char, size, 2, void)

/*
 * define kfifo_rec types
 */
struct kfifo_rec_ptr_1 __STRUCT_KFIFO_PTR(unsigned char, 1, void);
struct kfifo_rec_ptr_2 __STRUCT_KFIFO_PTR(unsigned char, 2, void);

/*
 * helper macro to distinguish between real in place fifo where the fifo
 * array is a part of the structure and the fifo type where the array is
 * outside of the fifo structure.
 */
#define    __is_kfifo_ptr(fifo)    (sizeof(*fifo) == sizeof(struct __kfifo))

/**
 * DECLARE_KFIFO_PTR - macro to declare a fifo pointer object
 * @fifo: name of the declared fifo
 * @type: type of the fifo elements
 */
#define DECLARE_KFIFO_PTR(fifo, type)    STRUCT_KFIFO_PTR(type) fifo

/**
 * DECLARE_KFIFO - macro to declare a fifo object
 * @fifo: name of the declared fifo
 * @type: type of the fifo elements
 * @size: the number of elements in the fifo, this must be a power of 2
 */
#define DECLARE_KFIFO(fifo, type, size)    STRUCT_KFIFO(type, size) fifo

/**
 * INIT_KFIFO - Initialize a fifo declared by DECLARE_KFIFO
 * @fifo: name of the declared fifo datatype
 */
#define INIT_KFIFO(fifo) 
(void)({ 
    typeof(&(fifo)) __tmp = &(fifo); 
    struct __kfifo *__kfifo = &__tmp->kfifo; 
    __kfifo->in = 0; 
    __kfifo->out = 0; 
    __kfifo->mask = __is_kfifo_ptr(__tmp) ? 0 : ARRAY_SIZE(__tmp->buf) - 1;
    __kfifo->esize = sizeof(*__tmp->buf); 
    __kfifo->data = __is_kfifo_ptr(__tmp) ?  NULL : __tmp->buf; 
})

/**
 * DEFINE_KFIFO - macro to define and initialize a fifo
 * @fifo: name of the declared fifo datatype
 * @type: type of the fifo elements
 * @size: the number of elements in the fifo, this must be a power of 2
 *
 * Note: the macro can be used for global and local fifo data type variables.
 */
#define DEFINE_KFIFO(fifo, type, size) 
    DECLARE_KFIFO(fifo, type, size) = 
    (typeof(fifo)) { 
        { 
            { 
            .in    = 0, 
            .out    = 0, 
            .mask    = __is_kfifo_ptr(&(fifo)) ? 
                  0 : 
                  ARRAY_SIZE((fifo).buf) - 1, 
            .esize    = sizeof(*(fifo).buf), 
            .data    = __is_kfifo_ptr(&(fifo)) ? 
                NULL : 
                (fifo).buf, 
            } 
        } 
    }


static inline unsigned int __must_check
__kfifo_uint_must_check_helper(unsigned int val)
{
    return val;
}

static inline int __must_check
__kfifo_int_must_check_helper(int val)
{
    return val;
}

/**
 * kfifo_initialized - Check if the fifo is initialized
 * @fifo: address of the fifo to check
 *
 * Return %true if fifo is initialized, otherwise %false.
 * Assumes the fifo was 0 before.
 */
#define kfifo_initialized(fifo) ((fifo)->kfifo.mask)

/**
 * kfifo_esize - returns the size of the element managed by the fifo
 * @fifo: address of the fifo to be used
 */
#define kfifo_esize(fifo)    ((fifo)->kfifo.esize)

/**
 * kfifo_recsize - returns the size of the record length field
 * @fifo: address of the fifo to be used
 */
#define kfifo_recsize(fifo)    (sizeof(*(fifo)->rectype))

/**
 * kfifo_size - returns the size of the fifo in elements
 * @fifo: address of the fifo to be used
 */
#define kfifo_size(fifo)    ((fifo)->kfifo.mask + 1)

/**
 * kfifo_reset - removes the entire fifo content
 * @fifo: address of the fifo to be used
 *
 * Note: usage of kfifo_reset() is dangerous. It should be only called when the
 * fifo is exclusived locked or when it is secured that no other thread is
 * accessing the fifo.
 */
#define kfifo_reset(fifo) 
(void)({ 
    typeof((fifo) + 1) __tmp = (fifo); 
    __tmp->kfifo.in = __tmp->kfifo.out = 0; 
})

/**
 * kfifo_reset_out - skip fifo content
 * @fifo: address of the fifo to be used
 *
 * Note: The usage of kfifo_reset_out() is safe until it will be only called
 * from the reader thread and there is only one concurrent reader. Otherwise
 * it is dangerous and must be handled in the same way as kfifo_reset().
 */
#define kfifo_reset_out(fifo)    
(void)({ 
    typeof((fifo) + 1) __tmp = (fifo); 
    __tmp->kfifo.out = __tmp->kfifo.in; 
})

/**
 * kfifo_len - returns the number of used elements in the fifo
 * @fifo: address of the fifo to be used
 */
#define kfifo_len(fifo) 
({ 
    typeof((fifo) + 1) __tmpl = (fifo); 
    __tmpl->kfifo.in - __tmpl->kfifo.out; 
})

/**
 * kfifo_is_empty - returns true if the fifo is empty
 * @fifo: address of the fifo to be used
 */
#define    kfifo_is_empty(fifo) 
({ 
    typeof((fifo) + 1) __tmpq = (fifo); 
    __tmpq->kfifo.in == __tmpq->kfifo.out; 
})

/**
 * kfifo_is_full - returns true if the fifo is full
 * @fifo: address of the fifo to be used
 */
#define    kfifo_is_full(fifo) 
({ 
    typeof((fifo) + 1) __tmpq = (fifo); 
    kfifo_len(__tmpq) > __tmpq->kfifo.mask; 
})

/**
 * kfifo_avail - returns the number of unused elements in the fifo
 * @fifo: address of the fifo to be used
 */
#define    kfifo_avail(fifo) 
__kfifo_uint_must_check_helper( 
({ 
    typeof((fifo) + 1) __tmpq = (fifo); 
    const size_t __recsize = sizeof(*__tmpq->rectype); 
    unsigned int __avail = kfifo_size(__tmpq) - kfifo_len(__tmpq); 
    (__recsize) ? ((__avail <= __recsize) ? 0 : 
    __kfifo_max_r(__avail - __recsize, __recsize)) : 
    __avail; 
}) 
)

/**
 * kfifo_skip - skip output data
 * @fifo: address of the fifo to be used
 */
#define    kfifo_skip(fifo) 
(void)({ 
    typeof((fifo) + 1) __tmp = (fifo); 
    const size_t __recsize = sizeof(*__tmp->rectype); 
    struct __kfifo *__kfifo = &__tmp->kfifo; 
    if (__recsize) 
        __kfifo_skip_r(__kfifo, __recsize); 
    else 
        __kfifo->out++; 
})

/**
 * kfifo_peek_len - gets the size of the next fifo record
 * @fifo: address of the fifo to be used
 *
 * This function returns the size of the next fifo record in number of bytes.
 */
#define kfifo_peek_len(fifo) 
__kfifo_uint_must_check_helper( 
({ 
    typeof((fifo) + 1) __tmp = (fifo); 
    const size_t __recsize = sizeof(*__tmp->rectype); 
    struct __kfifo *__kfifo = &__tmp->kfifo; 
    (!__recsize) ? kfifo_len(__tmp) * sizeof(*__tmp->type) : 
    __kfifo_len_r(__kfifo, __recsize); 
}) 
)

/**
 * kfifo_alloc - dynamically allocates a new fifo buffer
 * @fifo: pointer to the fifo
 * @size: the number of elements in the fifo, this must be a power of 2
 * @gfp_mask: get_free_pages mask, passed to kmalloc()
 *
 * This macro dynamically allocates a new fifo buffer.
 *
 * The numer of elements will be rounded-up to a power of 2.
 * The fifo will be release with kfifo_free().
 * Return 0 if no error, otherwise an error code.
 */
#define kfifo_alloc(fifo, size, gfp_mask) 
__kfifo_int_must_check_helper( 
({ 
    typeof((fifo) + 1) __tmp = (fifo); 
    struct __kfifo *__kfifo = &__tmp->kfifo; 
    __is_kfifo_ptr(__tmp) ? 
    __kfifo_alloc(__kfifo, size, sizeof(*__tmp->type), gfp_mask) : 
    -EINVAL; 
}) 
)

/**
 * kfifo_free - frees the fifo
 * @fifo: the fifo to be freed
 */
#define kfifo_free(fifo) 
({ 
    typeof((fifo) + 1) __tmp = (fifo); 
    struct __kfifo *__kfifo = &__tmp->kfifo; 
    if (__is_kfifo_ptr(__tmp)) 
        __kfifo_free(__kfifo); 
})

/**
 * kfifo_init - initialize a fifo using a preallocated buffer
 * @fifo: the fifo to assign the buffer
 * @buffer: the preallocated buffer to be used
 * @size: the size of the internal buffer, this have to be a power of 2
 *
 * This macro initialize a fifo using a preallocated buffer.
 *
 * The numer of elements will be rounded-up to a power of 2.
 * Return 0 if no error, otherwise an error code.
 */
#define kfifo_init(fifo, buffer, size) 
({ 
    typeof((fifo) + 1) __tmp = (fifo); 
    struct __kfifo *__kfifo = &__tmp->kfifo; 
    __is_kfifo_ptr(__tmp) ? 
    __kfifo_init(__kfifo, buffer, size, sizeof(*__tmp->type)) : 
    -EINVAL; 
})

/**
 * kfifo_put - put data into the fifo
 * @fifo: address of the fifo to be used
 * @val: the data to be added
 *
 * This macro copies the given value into the fifo.
 * It returns 0 if the fifo was full. Otherwise it returns the number
 * processed elements.
 *
 * Note that with only one concurrent reader and one concurrent
 * writer, you don't need extra locking to use these macro.
 */
#define    kfifo_put(fifo, val) 
({ 
    typeof((fifo) + 1) __tmp = (fifo); 
    typeof((val) + 1) __val = (val); 
    unsigned int __ret; 
    const size_t __recsize = sizeof(*__tmp->rectype); 
    struct __kfifo *__kfifo = &__tmp->kfifo; 
    if (0) { 
        typeof(__tmp->ptr_const) __dummy __attribute__ ((unused)); 
        __dummy = (typeof(__val))NULL; 
    } 
    if (__recsize) 
        __ret = __kfifo_in_r(__kfifo, __val, sizeof(*__val), 
            __recsize); 
    else { 
        __ret = !kfifo_is_full(__tmp); 
        if (__ret) { 
            (__is_kfifo_ptr(__tmp) ? 
            ((typeof(__tmp->type))__kfifo->data) : 
            (__tmp->buf) 
            )[__kfifo->in & __tmp->kfifo.mask] = 
                *(typeof(__tmp->type))__val; 
            smp_wmb(); 
            __kfifo->in++; 
        } 
    } 
    __ret; 
})

/**
 * kfifo_get - get data from the fifo
 * @fifo: address of the fifo to be used
 * @val: the var where to store the data to be added
 *
 * This macro reads the data from the fifo.
 * It returns 0 if the fifo was empty. Otherwise it returns the number
 * processed elements.
 *
 * Note that with only one concurrent reader and one concurrent
 * writer, you don't need extra locking to use these macro.
 */
#define    kfifo_get(fifo, val) 
__kfifo_uint_must_check_helper( 
({ 
    typeof((fifo) + 1) __tmp = (fifo); 
    typeof((val) + 1) __val = (val); 
    unsigned int __ret; 
    const size_t __recsize = sizeof(*__tmp->rectype); 
    struct __kfifo *__kfifo = &__tmp->kfifo; 
    if (0) 
        __val = (typeof(__tmp->ptr))0; 
    if (__recsize) 
        __ret = __kfifo_out_r(__kfifo, __val, sizeof(*__val), 
            __recsize); 
    else { 
        __ret = !kfifo_is_empty(__tmp); 
        if (__ret) { 
            *(typeof(__tmp->type))__val = 
                (__is_kfifo_ptr(__tmp) ? 
                ((typeof(__tmp->type))__kfifo->data) : 
                (__tmp->buf) 
                )[__kfifo->out & __tmp->kfifo.mask]; 
            smp_wmb(); 
            __kfifo->out++; 
        } 
    } 
    __ret; 
}) 
)

/**
 * kfifo_peek - get data from the fifo without removing
 * @fifo: address of the fifo to be used
 * @val: the var where to store the data to be added
 *
 * This reads the data from the fifo without removing it from the fifo.
 * It returns 0 if the fifo was empty. Otherwise it returns the number
 * processed elements.
 *
 * Note that with only one concurrent reader and one concurrent
 * writer, you don't need extra locking to use these macro.
 */
#define    kfifo_peek(fifo, val) 
__kfifo_uint_must_check_helper( 
({ 
    typeof((fifo) + 1) __tmp = (fifo); 
    typeof((val) + 1) __val = (val); 
    unsigned int __ret; 
    const size_t __recsize = sizeof(*__tmp->rectype); 
    struct __kfifo *__kfifo = &__tmp->kfifo; 
    if (0) 
        __val = (typeof(__tmp->ptr))NULL; 
    if (__recsize) 
        __ret = __kfifo_out_peek_r(__kfifo, __val, sizeof(*__val), 
            __recsize); 
    else { 
        __ret = !kfifo_is_empty(__tmp); 
        if (__ret) { 
            *(typeof(__tmp->type))__val = 
                (__is_kfifo_ptr(__tmp) ? 
                ((typeof(__tmp->type))__kfifo->data) : 
                (__tmp->buf) 
                )[__kfifo->out & __tmp->kfifo.mask]; 
            smp_wmb(); 
        } 
    } 
    __ret; 
}) 
)

/**
 * kfifo_in - put data into the fifo
 * @fifo: address of the fifo to be used
 * @buf: the data to be added
 * @n: number of elements to be added
 *
 * This macro copies the given buffer into the fifo and returns the
 * number of copied elements.
 *
 * Note that with only one concurrent reader and one concurrent
 * writer, you don't need extra locking to use these macro.
 */
#define    kfifo_in(fifo, buf, n) 
({ 
    typeof((fifo) + 1) __tmp = (fifo); 
    typeof((buf) + 1) __buf = (buf); 
    unsigned long __n = (n); 
    const size_t __recsize = sizeof(*__tmp->rectype); 
    struct __kfifo *__kfifo = &__tmp->kfifo; 
    if (0) { 
        typeof(__tmp->ptr_const) __dummy __attribute__ ((unused)); 
        __dummy = (typeof(__buf))NULL; 
    } 
    (__recsize) ?
    __kfifo_in_r(__kfifo, __buf, __n, __recsize) : 
    __kfifo_in(__kfifo, __buf, __n); 
})

/**
 * kfifo_in_spinlocked - put data into the fifo using a spinlock for locking
 * @fifo: address of the fifo to be used
 * @buf: the data to be added
 * @n: number of elements to be added
 * @lock: pointer to the spinlock to use for locking
 *
 * This macro copies the given values buffer into the fifo and returns the
 * number of copied elements.
 */
#define    kfifo_in_spinlocked(fifo, buf, n, lock) 
({ 
    unsigned long __flags; 
    unsigned int __ret; 
    spin_lock_irqsave(lock, __flags); 
    __ret = kfifo_in(fifo, buf, n); 
    spin_unlock_irqrestore(lock, __flags); 
    __ret; 
})

/* alias for kfifo_in_spinlocked, will be removed in a future release */
#define kfifo_in_locked(fifo, buf, n, lock) 
        kfifo_in_spinlocked(fifo, buf, n, lock)

/**
 * kfifo_out - get data from the fifo
 * @fifo: address of the fifo to be used
 * @buf: pointer to the storage buffer
 * @n: max. number of elements to get
 *
 * This macro get some data from the fifo and return the numbers of elements
 * copied.
 *
 * Note that with only one concurrent reader and one concurrent
 * writer, you don't need extra locking to use these macro.
 */
#define    kfifo_out(fifo, buf, n) 
__kfifo_uint_must_check_helper( 
({ 
    typeof((fifo) + 1) __tmp = (fifo); 
    typeof((buf) + 1) __buf = (buf); 
    unsigned long __n = (n); 
    const size_t __recsize = sizeof(*__tmp->rectype); 
    struct __kfifo *__kfifo = &__tmp->kfifo; 
    if (0) { 
        typeof(__tmp->ptr) __dummy = NULL; 
        __buf = __dummy; 
    } 
    (__recsize) ?
    __kfifo_out_r(__kfifo, __buf, __n, __recsize) : 
    __kfifo_out(__kfifo, __buf, __n); 
}) 
)

/**
 * kfifo_out_spinlocked - get data from the fifo using a spinlock for locking
 * @fifo: address of the fifo to be used
 * @buf: pointer to the storage buffer
 * @n: max. number of elements to get
 * @lock: pointer to the spinlock to use for locking
 *
 * This macro get the data from the fifo and return the numbers of elements
 * copied.
 */
#define    kfifo_out_spinlocked(fifo, buf, n, lock) 
__kfifo_uint_must_check_helper( 
({ 
    unsigned long __flags; 
    unsigned int __ret; 
    spin_lock_irqsave(lock, __flags); 
    __ret = kfifo_out(fifo, buf, n); 
    spin_unlock_irqrestore(lock, __flags); 
    __ret; 
}) 
)

/* alias for kfifo_out_spinlocked, will be removed in a future release */
#define kfifo_out_locked(fifo, buf, n, lock) 
        kfifo_out_spinlocked(fifo, buf, n, lock)

/**
 * kfifo_from_user - puts some data from user space into the fifo
 * @fifo: address of the fifo to be used
 * @from: pointer to the data to be added
 * @len: the length of the data to be added
 * @copied: pointer to output variable to store the number of copied bytes
 *
 * This macro copies at most @len bytes from the @from into the
 * fifo, depending of the available space and returns -EFAULT/0.
 *
 * Note that with only one concurrent reader and one concurrent
 * writer, you don't need extra locking to use these macro.
 */
#define    kfifo_from_user(fifo, from, len, copied) 
__kfifo_uint_must_check_helper( 
({ 
    typeof((fifo) + 1) __tmp = (fifo); 
    const void __user *__from = (from); 
    unsigned int __len = (len); 
    unsigned int *__copied = (copied); 
    const size_t __recsize = sizeof(*__tmp->rectype); 
    struct __kfifo *__kfifo = &__tmp->kfifo; 
    (__recsize) ? 
    __kfifo_from_user_r(__kfifo, __from, __len,  __copied, __recsize) : 
    __kfifo_from_user(__kfifo, __from, __len, __copied); 
}) 
)

/**
 * kfifo_to_user - copies data from the fifo into user space
 * @fifo: address of the fifo to be used
 * @to: where the data must be copied
 * @len: the size of the destination buffer
 * @copied: pointer to output variable to store the number of copied bytes
 *
 * This macro copies at most @len bytes from the fifo into the
 * @to buffer and returns -EFAULT/0.
 *
 * Note that with only one concurrent reader and one concurrent
 * writer, you don't need extra locking to use these macro.
 */
#define    kfifo_to_user(fifo, to, len, copied) 
__kfifo_uint_must_check_helper( 
({ 
    typeof((fifo) + 1) __tmp = (fifo); 
    void __user *__to = (to); 
    unsigned int __len = (len); 
    unsigned int *__copied = (copied); 
    const size_t __recsize = sizeof(*__tmp->rectype); 
    struct __kfifo *__kfifo = &__tmp->kfifo; 
    (__recsize) ? 
    __kfifo_to_user_r(__kfifo, __to, __len, __copied, __recsize) : 
    __kfifo_to_user(__kfifo, __to, __len, __copied); 
}) 
)

/**
 * kfifo_dma_in_prepare - setup a scatterlist for DMA input
 * @fifo: address of the fifo to be used
 * @sgl: pointer to the scatterlist array
 * @nents: number of entries in the scatterlist array
 * @len: number of elements to transfer
 *
 * This macro fills a scatterlist for DMA input.
 * It returns the number entries in the scatterlist array.
 *
 * Note that with only one concurrent reader and one concurrent
 * writer, you don't need extra locking to use these macros.
 */
#define    kfifo_dma_in_prepare(fifo, sgl, nents, len) 
({ 
    typeof((fifo) + 1) __tmp = (fifo); 
    struct scatterlist *__sgl = (sgl); 
    int __nents = (nents); 
    unsigned int __len = (len); 
    const size_t __recsize = sizeof(*__tmp->rectype); 
    struct __kfifo *__kfifo = &__tmp->kfifo; 
    (__recsize) ? 
    __kfifo_dma_in_prepare_r(__kfifo, __sgl, __nents, __len, __recsize) : 
    __kfifo_dma_in_prepare(__kfifo, __sgl, __nents, __len); 
})

/**
 * kfifo_dma_in_finish - finish a DMA IN operation
 * @fifo: address of the fifo to be used
 * @len: number of bytes to received
 *
 * This macro finish a DMA IN operation. The in counter will be updated by
 * the len parameter. No error checking will be done.
 *
 * Note that with only one concurrent reader and one concurrent
 * writer, you don't need extra locking to use these macros.
 */
#define kfifo_dma_in_finish(fifo, len) 
(void)({ 
    typeof((fifo) + 1) __tmp = (fifo); 
    unsigned int __len = (len); 
    const size_t __recsize = sizeof(*__tmp->rectype); 
    struct __kfifo *__kfifo = &__tmp->kfifo; 
    if (__recsize) 
        __kfifo_dma_in_finish_r(__kfifo, __len, __recsize); 
    else 
        __kfifo->in += __len / sizeof(*__tmp->type); 
})

/**
 * kfifo_dma_out_prepare - setup a scatterlist for DMA output
 * @fifo: address of the fifo to be used
 * @sgl: pointer to the scatterlist array
 * @nents: number of entries in the scatterlist array
 * @len: number of elements to transfer
 *
 * This macro fills a scatterlist for DMA output which at most @len bytes
 * to transfer.
 * It returns the number entries in the scatterlist array.
 * A zero means there is no space available and the scatterlist is not filled.
 *
 * Note that with only one concurrent reader and one concurrent
 * writer, you don't need extra locking to use these macros.
 */
#define    kfifo_dma_out_prepare(fifo, sgl, nents, len) 
({ 
    typeof((fifo) + 1) __tmp = (fifo);  
    struct scatterlist *__sgl = (sgl); 
    int __nents = (nents); 
    unsigned int __len = (len); 
    const size_t __recsize = sizeof(*__tmp->rectype); 
    struct __kfifo *__kfifo = &__tmp->kfifo; 
    (__recsize) ? 
    __kfifo_dma_out_prepare_r(__kfifo, __sgl, __nents, __len, __recsize) : 
    __kfifo_dma_out_prepare(__kfifo, __sgl, __nents, __len); 
})

/**
 * kfifo_dma_out_finish - finish a DMA OUT operation
 * @fifo: address of the fifo to be used
 * @len: number of bytes transferd
 *
 * This macro finish a DMA OUT operation. The out counter will be updated by
 * the len parameter. No error checking will be done.
 *
 * Note that with only one concurrent reader and one concurrent
 * writer, you don't need extra locking to use these macros.
 */
#define kfifo_dma_out_finish(fifo, len) 
(void)({ 
    typeof((fifo) + 1) __tmp = (fifo); 
    unsigned int __len = (len); 
    const size_t __recsize = sizeof(*__tmp->rectype); 
    struct __kfifo *__kfifo = &__tmp->kfifo; 
    if (__recsize) 
        __kfifo_dma_out_finish_r(__kfifo, __recsize); 
    else 
        __kfifo->out += __len / sizeof(*__tmp->type); 
})

/**
 * kfifo_out_peek - gets some data from the fifo
 * @fifo: address of the fifo to be used
 * @buf: pointer to the storage buffer
 * @n: max. number of elements to get
 *
 * This macro get the data from the fifo and return the numbers of elements
 * copied. The data is not removed from the fifo.
 *
 * Note that with only one concurrent reader and one concurrent
 * writer, you don't need extra locking to use these macro.
 */
#define    kfifo_out_peek(fifo, buf, n) 
__kfifo_uint_must_check_helper( 
({ 
    typeof((fifo) + 1) __tmp = (fifo); 
    typeof((buf) + 1) __buf = (buf); 
    unsigned long __n = (n); 
    const size_t __recsize = sizeof(*__tmp->rectype); 
    struct __kfifo *__kfifo = &__tmp->kfifo; 
    if (0) { 
        typeof(__tmp->ptr) __dummy __attribute__ ((unused)) = NULL; 
        __buf = __dummy; 
    } 
    (__recsize) ? 
    __kfifo_out_peek_r(__kfifo, __buf, __n, __recsize) : 
    __kfifo_out_peek(__kfifo, __buf, __n); 
}) 
)

extern int __kfifo_alloc(struct __kfifo *fifo, unsigned int size,
    size_t esize, gfp_t gfp_mask);

extern void __kfifo_free(struct __kfifo *fifo);

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

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

extern unsigned int __kfifo_out(struct __kfifo *fifo,
    void *buf, unsigned int len);

extern int __kfifo_from_user(struct __kfifo *fifo,
    const void __user *from, unsigned long len, unsigned int *copied);

extern int __kfifo_to_user(struct __kfifo *fifo,
    void __user *to, unsigned long len, unsigned int *copied);

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

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

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

extern unsigned int __kfifo_in_r(struct __kfifo *fifo,
    const void *buf, unsigned int len, size_t recsize);

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

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

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

extern unsigned int __kfifo_dma_in_prepare_r(struct __kfifo *fifo,
    struct scatterlist *sgl, int nents, unsigned int len, size_t recsize);

extern void __kfifo_dma_in_finish_r(struct __kfifo *fifo,
    unsigned int len, size_t recsize);

extern unsigned int __kfifo_dma_out_prepare_r(struct __kfifo *fifo,
    struct scatterlist *sgl, int nents, unsigned int len, size_t recsize);

extern void __kfifo_dma_out_finish_r(struct __kfifo *fifo, size_t recsize);

extern unsigned int __kfifo_len_r(struct __kfifo *fifo, size_t recsize);

extern void __kfifo_skip_r(struct __kfifo *fifo, size_t recsize);

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

extern unsigned int __kfifo_max_r(unsigned int len, size_t recsize);

#endif

　　如何使用请参考kernel其他文件使用  ：  DEFINE_KFIFO 　　kfifo_put　　kfifo_get

　　最重要的是存储的数据类型不仅是之前的unsigned char， 还可以是struct！ 这才牛逼！