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 */
};

static inline unsigned int kfifo_get(struct kfifo *fifo,
                                     unsigned char *buffer, unsigned int len)
{
    unsigned long flags;
    unsigned int ret;

    spin_lock_irqsave(fifo->lock, flags);
    ret = __kfifo_get(fifo, buffer, len);

    /*
     * optimization: if the FIFO is empty, set the indices to 0
     * so we don't wrap the next time
     */
    if (fifo->in == fifo->out)
        fifo->in = fifo->out = 0;

    spin_unlock_irqrestore(fifo->lock, flags);

    return ret;
}

/* first put the data starting from fifo->in to buffer end */
l = min(len, fifo->size - (fifo->in & (fifo->size - 1)));
memcpy(fifo->buffer + (fifo->in & (fifo->size - 1)), buffer, l);