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Commit 197a5212 authored by Michael S. Tsirkin's avatar Michael S. Tsirkin Committed by David S. Miller
Browse files

ptr_ring: add ptr_ring_unconsume 



Applications that consume a batch of entries in one go
can benefit from ability to return some of them back
into the ring.

Add an API for that - assuming there's space. If there's no space
naturally can't do this and have to drop entries, but this implies ring
is full so we'd likely drop some anyway.

Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarJason Wang <jasowang@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 1fc4d180

include/linux/ptr_ring.h

+55 −0
Original line number Original line Diff line number Diff line
@@ -403,6 +403,61 @@ static inline int ptr_ring_init(struct ptr_ring *r, int size, gfp_t gfp) 
	return 0;

	return 0;

}

}





/*

 * Return entries into ring. Destroy entries that don't fit.

 *

 * Note: this is expected to be a rare slow path operation.

 *

 * Note: producer lock is nested within consumer lock, so if you

 * resize you must make sure all uses nest correctly.

 * In particular if you consume ring in interrupt or BH context, you must

 * disable interrupts/BH when doing so.

 */

static inline void ptr_ring_unconsume(struct ptr_ring *r, void **batch, int n,

				      void (*destroy)(void *))

{

	unsigned long flags;

	int head;



	spin_lock_irqsave(&r->consumer_lock, flags);

	spin_lock(&r->producer_lock);



	if (!r->size)

		goto done;



	/*

	 * Clean out buffered entries (for simplicity). This way following code

	 * can test entries for NULL and if not assume they are valid.

	 */

	head = r->consumer_head - 1;

	while (likely(head >= r->consumer_tail))

		r->queue[head--] = NULL;

	r->consumer_tail = r->consumer_head;



	/*

	 * Go over entries in batch, start moving head back and copy entries.

	 * Stop when we run into previously unconsumed entries.

	 */

	while (n) {

		head = r->consumer_head - 1;

		if (head < 0)

			head = r->size - 1;

		if (r->queue[head]) {

			/* This batch entry will have to be destroyed. */

			goto done;

		}

		r->queue[head] = batch[--n];

		r->consumer_tail = r->consumer_head = head;

	}



done:

	/* Destroy all entries left in the batch. */

	while (n)

		destroy(batch[--n]);

	spin_unlock(&r->producer_lock);

	spin_unlock_irqrestore(&r->consumer_lock, flags);

}



static inline void **__ptr_ring_swap_queue(struct ptr_ring *r, void **queue,

static inline void **__ptr_ring_swap_queue(struct ptr_ring *r, void **queue,

					   int size, gfp_t gfp,

					   int size, gfp_t gfp,

					   void (*destroy)(void *))

					   void (*destroy)(void *))