/*  Simple queue management  */
struct v4l2_q_node
{
        struct v4l2_q_node      *forw, *back;
};
struct v4l2_queue
{
        struct v4l2_q_node      *forw, *back;
                rwlock_t                qlock;  
};
/*
 *  Simple queue management
 */
static rwlock_t rw_lock_unlocked = RW_LOCK_UNLOCKED;
void
v4l2_q_init(struct v4l2_queue *q)
{
	if (q == NULL)
		return;
	q->qlock = rw_lock_unlocked;
	q->forw = (struct v4l2_q_node *)q;
	q->back = (struct v4l2_q_node *)q;
}
void
v4l2_q_add_head(struct v4l2_queue *q, struct v4l2_q_node *node)
{
	unsigned long flags;
	if (q == NULL || node == NULL)
		return;
	if (q->forw == NULL || q->back == NULL)
		v4l2_q_init(q);
	write_lock_irqsave(&(q->qlock), flags);
	node->forw = q->forw;
	node->back = (struct v4l2_q_node *)q;
	q->forw->back = node;
	q->forw = node;
	write_unlock_irqrestore(&(q->qlock), flags);
}
void
v4l2_q_add_tail(struct v4l2_queue *q, struct v4l2_q_node *node)
{
	unsigned long flags;
	if (q == NULL || node == NULL)
		return;
	if (q->forw == NULL || q->back == NULL)
		v4l2_q_init(q);
	write_lock_irqsave(&(q->qlock), flags);
	node->forw = (struct v4l2_q_node *)q;
	node->back = q->back;
	q->back->forw = node;
	q->back = node;
	write_unlock_irqrestore(&(q->qlock), flags);
}
void *
v4l2_q_del_head(struct v4l2_queue *q)
{
	unsigned long flags;
	struct v4l2_q_node *node;
	if (q == NULL)
		return NULL;
	write_lock_irqsave(&(q->qlock), flags);
	if (q->forw == NULL || q->back == NULL ||
	    q->forw == (struct v4l2_q_node *)q ||
	    q->back == (struct v4l2_q_node *)q)
	{
		write_unlock_irqrestore(&(q->qlock), flags);
		return NULL;
	}
	node = q->forw;
	node->forw->back = (struct v4l2_q_node *)q;
	q->forw = node->forw;
	node->forw = NULL;
	node->back = NULL;
	write_unlock_irqrestore(&(q->qlock), flags);
	return node;
}
void *
v4l2_q_del_tail(struct v4l2_queue *q)
{
	unsigned long flags;
	struct v4l2_q_node *node;
	if (q == NULL)
		return NULL;
	write_lock_irqsave(&(q->qlock), flags);
	if (q->forw == NULL || q->back == NULL ||
	    q->forw == (struct v4l2_q_node *)q ||
	    q->back == (struct v4l2_q_node *)q)
	{
		write_unlock_irqrestore(&(q->qlock), flags);
		return NULL;
	}
	node = q->back;
	node->back->forw = (struct v4l2_q_node *)q;
	q->back = node->back;
	node->forw = NULL;
	node->back = NULL;
	write_unlock_irqrestore(&(q->qlock), flags);
	return node;
}
void *
v4l2_q_peek_head(struct v4l2_queue *q)
{
	unsigned long flags;
	struct v4l2_q_node *node;
	read_lock_irqsave(&(q->qlock), flags);
	if (q == NULL || q->forw == NULL || q->forw == (struct v4l2_q_node *)q)
	{
		read_unlock_irqrestore(&(q->qlock), flags);
		return NULL;
	}
	node = q->forw;
	read_unlock_irqrestore(&(q->qlock), flags);
	return node;
}
void *
v4l2_q_peek_tail(struct v4l2_queue *q)
{
	unsigned long flags;
	struct v4l2_q_node *node;
	read_lock_irqsave(&(q->qlock), flags);
	if (q == NULL || q->back == NULL || q->back == (struct v4l2_q_node *)q)
	{
		read_unlock_irqrestore(&(q->qlock), flags);
		return NULL;
	}
	node = q->back;
	read_unlock_irqrestore(&(q->qlock), flags);
	return node;
}
void *
v4l2_q_yank_node(struct v4l2_queue *q, struct v4l2_q_node *node)
{
	unsigned long flags;
	struct v4l2_q_node *t;
	if (v4l2_q_peek_head(q) == NULL || node == NULL)
		return NULL;
	write_lock_irqsave(&(q->qlock), flags);
	for (t = q->forw; t != (struct v4l2_q_node *)q; t = t->forw)
		if (t == node)
		{
			node->back->forw = node->forw;
			node->forw->back = node->back;
			node->forw = NULL;
			node->back = NULL;
			write_unlock_irqrestore(&(q->qlock), flags);
			return node;
		}
	write_unlock_irqrestore(&(q->qlock), flags);
	return NULL;
}
int
v4l2_q_last(struct v4l2_queue *q)
{
/*  This function by Olivier Carmona  */

	unsigned long flags;
	read_lock_irqsave(&(q->qlock), flags);
	if (q == NULL)
	{
		read_unlock_irqrestore(&(q->qlock), flags);
		return -1;
	}
	if (q->forw == NULL || q->back == NULL ||
	    q->forw == (struct v4l2_q_node *)q ||
	    q->back == (struct v4l2_q_node *)q)
	{
		read_unlock_irqrestore(&(q->qlock), flags);
		return -1;
	}
	if (q->forw == q->back)
	{
		read_unlock_irqrestore(&(q->qlock), flags);
		return 1;
	}
	read_unlock_irqrestore(&(q->qlock), flags);
	return 0;
}

extern void  v4l2_q_init(struct v4l2_queue *q);
extern void  v4l2_q_add_head(struct v4l2_queue *q, struct v4l2_q_node *node); 
extern void  v4l2_q_add_tail(struct v4l2_queue *q, struct v4l2_q_node *node); 
extern void *v4l2_q_del_head(struct v4l2_queue *q);
extern void *v4l2_q_del_tail(struct v4l2_queue *q);
extern void *v4l2_q_peek_head(struct v4l2_queue *q);
extern void *v4l2_q_peek_tail(struct v4l2_queue *q);
extern void *v4l2_q_yank_node(struct v4l2_queue *q, struct v4l2_q_node *node); 
extern int   v4l2_q_last(struct v4l2_queue *q);