linux kfifo的使用

Linux kfifo的使用
基于3.10-lsti内核
Kfifo也叫内核队列。
1.首先定义struct kfifo fifo;
2. kfifo初始化。
方法一：动态分配并初始化
Int kfifo_alloc(struct kfifo *fifo, unsigned int size, gfp_t  gfp_mask)
* 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.
Size大小最好为2的幂。
   ret = kfifo_alloc(&fpga_uart_device.fifo,1024,GFP_KERNEL);
方法二：先分配空间，在初始化。
/**
 * 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; \
})


3. 入fifo /**
 * 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)


4.出fifo /**
 * 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)
5. 返回fifo内部元素的个数 /**
 * kfifo_len - returns the number of used elements in the fifo
 * @fifo: address of the fifo to be used
 */
#define kfifo_len(fifo)


count = kfifo_len(&g_uart_devicep->fifo);
6. 返回fifo内部未使用空间的个数
/**
 * kfifo_avail - returns the number of unused elements in the fifo
 * @fifo: address of the fifo to be used
 */
#define kfifo_avail(fifo)
7. puts some data from user space into the fifo
/**
 * 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)
8. copies data from the fifo into user space
/**
 * 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)


9. /**
 * kfifo_free - frees the fifo
 * @fifo: the fifo to be freed
 */
#define kfifo_free(fifo)






应用样例：
Int ret=0;
Int count = 0;
Unsigned char tempbuf[1024] = {0};
struct kfifo fifo; 


ret = kfifo_alloc(&fifo, 1024, GFP_KERNEL);//分配1024个大小的空间，并初始化。
if(ret)//返回值为非0，代表出错。
return error;


count = kfifo_len(&fifo);//查看fifo空间里的元素个数。
count = kfifo_avail(fifo);//查看fifo空间里空闲的个数。


count = kfifo_in(&fifo,(void *)(tempbuf),20);//入队列20个字节到fifo中。返回成功copy的个数。
count = kfifo_out(&fifo,(void *)(tempbuf),20);//出队列20个字节到tempbuf中。返回成功copy的个数。


ret = kfifo_to_user(&fifo, (void *)_usr,20,&copied);//出队列20个字节到用户空间，copied为copy成功的字节数。
ret = kfifo_from_user(&fifo, (void *) _usr, 20, &copied);// 从用记空间copy 20个字节到队列中，copied为copy成功的字节数。