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/* SPDX-License-Identifier: GPL-2.0-only */
#ifndef LWQ_H
#define LWQ_H
/*
* Light-weight single-linked queue built from llist
*
* Entries can be enqueued from any context with no locking.
* Entries can be dequeued from process context with integrated locking.
*
* This is particularly suitable when work items are queued in
* BH or IRQ context, and where work items are handled one at a time
* by dedicated threads.
*/
#include <linux/container_of.h>
#include <linux/spinlock.h>
#include <linux/llist.h>
struct lwq_node {
struct llist_node node;
};
struct lwq {
spinlock_t lock;
struct llist_node *ready; /* entries to be dequeued */
struct llist_head new; /* entries being enqueued */
};
/**
* lwq_init - initialise a lwq
* @q: the lwq object
*/
static inline void lwq_init(struct lwq *q)
{
spin_lock_init(&q->lock);
q->ready = NULL;
init_llist_head(&q->new);
}
/**
* lwq_empty - test if lwq contains any entry
* @q: the lwq object
*
* This empty test contains an acquire barrier so that if a wakeup
* is sent when lwq_dequeue returns true, it is safe to go to sleep after
* a test on lwq_empty().
*/
static inline bool lwq_empty(struct lwq *q)
{
/* acquire ensures ordering wrt lwq_enqueue() */
return smp_load_acquire(&q->ready) == NULL && llist_empty(&q->new);
}
struct llist_node *__lwq_dequeue(struct lwq *q);
/**
* lwq_dequeue - dequeue first (oldest) entry from lwq
* @q: the queue to dequeue from
* @type: the type of object to return
* @member: them member in returned object which is an lwq_node.
*
* Remove a single object from the lwq and return it. This will take
* a spinlock and so must always be called in the same context, typcially
* process contet.
*/
#define lwq_dequeue(q, type, member) \
({ struct llist_node *_n = __lwq_dequeue(q); \
_n ? container_of(_n, type, member.node) : NULL; })
struct llist_node *lwq_dequeue_all(struct lwq *q);
/**
* lwq_for_each_safe - iterate over detached queue allowing deletion
* @_n: iterator variable
* @_t1: temporary struct llist_node **
* @_t2: temporary struct llist_node *
* @_l: address of llist_node pointer from lwq_dequeue_all()
* @_member: member in _n where lwq_node is found.
*
* Iterate over members in a dequeued list. If the iterator variable
* is set to NULL, the iterator removes that entry from the queue.
*/
#define lwq_for_each_safe(_n, _t1, _t2, _l, _member) \
for (_t1 = (_l); \
*(_t1) ? (_n = container_of(*(_t1), typeof(*(_n)), _member.node),\
_t2 = ((*_t1)->next), \
true) \
: false; \
(_n) ? (_t1 = &(_n)->_member.node.next, 0) \
: ((*(_t1) = (_t2)), 0))
/**
* lwq_enqueue - add a new item to the end of the queue
* @n - the lwq_node embedded in the item to be added
* @q - the lwq to append to.
*
* No locking is needed to append to the queue so this can
* be called from any context.
* Return %true is the list may have previously been empty.
*/
static inline bool lwq_enqueue(struct lwq_node *n, struct lwq *q)
{
/* acquire enqures ordering wrt lwq_dequeue */
return llist_add(&n->node, &q->new) &&
smp_load_acquire(&q->ready) == NULL;
}
/**
* lwq_enqueue_batch - add a list of new items to the end of the queue
* @n - the lwq_node embedded in the first item to be added
* @q - the lwq to append to.
*
* No locking is needed to append to the queue so this can
* be called from any context.
* Return %true is the list may have previously been empty.
*/
static inline bool lwq_enqueue_batch(struct llist_node *n, struct lwq *q)
{
struct llist_node *e = n;
/* acquire enqures ordering wrt lwq_dequeue */
return llist_add_batch(llist_reverse_order(n), e, &q->new) &&
smp_load_acquire(&q->ready) == NULL;
}
#endif /* LWQ_H */
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