本文主要是介绍kfifo 用户空间实现，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
按照linux内核对kfifo的实现，修改成用户空间的kfifo，kfifo是一个循环存储队列，队列是一个大块内存，通过in和out指针管理进和出队列。比较适合大小固定的数据存储。这里的实现没有加锁机制！内核kfifo原理，参考http://blog.csdn.net/linyt/article/details/5764312
kfifo头文件。
#ifndef _Linux_KFIFO_H
#define _Linux_KFIFO_H#define __u32 unsigned long
#define __u64 unsigned long long#define min(x,y) ((x) < (y) ? (x) : (y) )#define max(x,y) ((x) > (y) ? (x) : (y) )
/*
static inline int fls(int x)
{int r;__asm__("bsrl %1,%0nt""jnz 1fnt""movl $-1,%0n""1:" : "=r" (r) : "rm" (x));return r+1;
}*/
static inline int fls(int x)
{int r = 32; if (!x)return 0;if (!(x & 0xffff0000u)) {x <<= 16; r -= 16; } if (!(x & 0xff000000u)) {x <<= 8;r -= 8;} if (!(x & 0xf0000000u)) {x <<= 4;r -= 4;} if (!(x & 0xc0000000u)) {x <<= 2;r -= 2;} if (!(x & 0x80000000u)) {x <<= 1;r -= 1;} return r;
}static inline int fls64(__u64 x)
{__u32 h = x >> 32;if (h)return fls(h) + 32;return fls(x);
}static inline unsigned fls_long(unsigned long l)
{if (sizeof(l) == 4)return fls(l);return fls64(l);
}static inline unsigned long roundup_pow_of_two(unsigned long x)
{return 1UL << fls_long(x - 1);
}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) */
};struct kfifo *kfifo_init(unsigned char *buffer, unsigned int size);
struct kfifo *kfifo_alloc(unsigned int size);
void kfifo_free(struct kfifo *fifo);
unsigned int __kfifo_put(struct kfifo *fifo, unsigned char *buffer, unsigned int len);
unsigned int __kfifo_get(struct kfifo *fifo, unsigned char *buffer, unsigned int len);static inline void __kfifo_reset(struct kfifo *fifo)
{fifo->in = fifo->out = 0;
}static inline void kfifo_reset(struct kfifo *fifo)
{__kfifo_reset(fifo);}static inline unsigned int kfifo_put(struct kfifo *fifo,unsigned char *buffer, unsigned int len)
{unsigned int ret;ret = __kfifo_put(fifo, buffer, len);return ret;
}static inline unsigned int kfifo_get(struct kfifo *fifo,unsigned char *buffer, unsigned int len)
{unsigned int ret;ret = __kfifo_get(fifo, buffer, len);if (fifo->in == fifo->out)fifo->in = fifo->out = 0;return ret;
}static inline unsigned int __kfifo_len(struct kfifo *fifo)
{return fifo->in - fifo->out;
}static inline unsigned int kfifo_len(struct kfifo *fifo)
{unsigned int ret;ret = __kfifo_len(fifo);return ret;
}#endif#include "kfifo.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct kfifo *kfifo_init(unsigned char *buffer, unsigned int size)
{struct kfifo *fifo;fifo = (struct kfifo *)malloc(sizeof(struct kfifo));if (!fifo)return NULL;fifo->buffer = buffer;fifo->size = size;fifo->in = fifo->out = 0;return fifo;
}struct kfifo *kfifo_alloc(unsigned int size)
{unsigned char *buffer;struct kfifo *ret;if (size & (size - 1)) {fprintf(stderr,"size > 0x80000000n");size = roundup_pow_of_two(size);}buffer = (unsigned char *)malloc(size);if (!buffer)return NULL;ret = kfifo_init(buffer, size);if ((unsigned long)ret <= 0){free(buffer);}return ret;
}void kfifo_free(struct kfifo *fifo)
{free(fifo->buffer);free(fifo);
}unsigned int __kfifo_put(struct kfifo *fifo, unsigned char *buffer, unsigned int len)
{unsigned int l;len = min(len, fifo->size - fifo->in + fifo->out);l = min(len, fifo->size - (fifo->in & (fifo->size - 1)));memcpy(fifo->buffer + (fifo->in & (fifo->size - 1)), buffer, l);memcpy(fifo->buffer, buffer + l, len - l);fifo->in += len;return len;
}unsigned int __kfifo_get(struct kfifo *fifo,unsigned char *buffer, unsigned int len)
{unsigned int l;len = min(len, fifo->in - fifo->out);l = min(len, fifo->size - (fifo->out & (fifo->size - 1)));memcpy(buffer, fifo->buffer + (fifo->out & (fifo->size - 1)), l);fifo->out += len;return len;
}kfifo测试（来自网友的代码）
#define FIFO_LENGTH 4096
#include <stdio.h>
#include <pthread.h>
#include <strings.h>
#include <string.h>
#include "kfifo.h"
struct ll_param
{struct kfifo * fifo;int msg_len;
};static struct ll_param fifo;void thread_reader(void * param)
{int read_len=0;unsigned int counter=0;unsigned char buffer[FIFO_LENGTH];struct ll_param * p=(struct ll_param *)param;printf("nnn = %d\n", roundup_pow_of_two(5)); for(;;){bzero(buffer, FIFO_LENGTH);read_len=kfifo_get(p->fifo, buffer, 25);if(read_len !=0 ){printf("Read len:%d, buffer is :< %s >n\n", read_len, buffer);}else{counter++;}if(counter > 20){break;}usleep(50000);}
}void thread_writer(void * param)
{unsigned int write_len = 0;unsigned int counter = 0;unsigned char buffer[32];struct ll_param * p = (struct ll_param *)param;for(counter = 0; counter < 100; counter++){bzero(buffer,32);sprintf((char *)buffer, "This is %d message.n", counter);write_len=kfifo_put(p->fifo, buffer, 25); //strlen((char *)buffer)usleep(100);}
}int main(void)
{pthread_t pidr;pthread_t pidw;fifo.msg_len = 10;fifo.fifo = kfifo_alloc(FIFO_LENGTH);pthread_create(&pidw, NULL, (void *)thread_writer, &fifo);pthread_create(&pidr, NULL, (void *)thread_reader, &fifo);pthread_join(pidr, NULL);pthread_join(pidw, NULL);kfifo_free(fifo.fifo);printf("nGoodbye!n\n");return 0;
}Makefile
CFLAGS = -O2 -Wall
INCLUDE = -I /
CC = gcc test:test.o kfifo.o${CC} ${CFLAGS} test.o kfifo.o -o $@ ${INCLUDE} -pthreadtest.o:$(CC) -c test.c ${INCLUDE} -pthread
kfifo.o:$(CC) -c kfifo.c ${INCLUDE}
clean:rm -rf *.o test这篇关于kfifo 用户空间实现的文章就介绍到这儿，希望我们推荐的文章对编程师们有所帮助！
