Linux内核之内核数据结构

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) */
	spinlock_t *lock;	/* protects concurrent modifications */
};

struct kfifo *kfifo_alloc(unsigned int size, int 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' tachnique works only in this case.
	 */
	if (size & (size - 1)) { //判断size是否是二的幂
		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;
}

unsigned int __kfifo_put(struct kfifo *fifo,
			 unsigned char *buffer, unsigned int len)//buffer是要加入队列的数据，len是buffer的长度
{
	unsigned int l;

	len = min(len, fifo->size - fifo->in + fifo->out);//需要长度和空闲长度的最小值

	/* first put the data starting from fifo->in to buffer end */
	l = min(len, fifo->size - (fifo->in & (fifo->size - 1)));//需要长度和末端长度的最小值
	memcpy(fifo->buffer + (fifo->in & (fifo->size - 1)), buffer, l);//一部分放到末端

	/* then put the rest (if any) at the beginning of the buffer */
	memcpy(fifo->buffer, buffer + l, len - l);//一部分放到起端

	fifo->in += len;//in和out始终是线性增大的，但溢出的时候，重新从0开始增长

	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);

	/* 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);//to,from

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

	fifo->out += len;

	return len;
}