[PATCH RFC v7 4/5] ptr_ring: resize support

["Michael S. Tsirkin" <mst@redhat.com>]

This adds ring resize support. Seems to be necessary as
users such as tun allow userspace control over queue size.

If resize is used, this costs us ability to peek at queue without
consumer lock - should not be a big deal as peek and consumer are
usually run on the same CPU.

If ring is made bigger, ring contents is preserved.  If ring is made
smaller, extra pointers are passed to an optional destructor callback.

Cleanup function also gains destructor callback such that
all pointers in queue can be cleaned up.

This changes some APIs but we don't have any users yet,
so it won't break bisect.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 include/linux/ptr_ring.h | 157 ++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 143 insertions(+), 14 deletions(-)

diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
index d265d72..effb6d3 100644
--- a/include/linux/ptr_ring.h
+++ b/include/linux/ptr_ring.h
@@ -43,9 +43,9 @@ struct ptr_ring {
 };
 
 /* Note: callers invoking this in a loop must use a compiler barrier,
- * for example cpu_relax().
- * Callers don't need to take producer lock - if they don't
- * the next call to __ptr_ring_produce may fail.
+ * for example cpu_relax().  If ring is ever resized, callers must hold
+ * producer_lock - see e.g. ptr_ring_full.  Otherwise, if callers don't hold
+ * producer_lock, the next call to __ptr_ring_produce may fail.
  */
 static inline bool __ptr_ring_full(struct ptr_ring *r)
 {
@@ -54,16 +54,55 @@ static inline bool __ptr_ring_full(struct ptr_ring *r)
 
 static inline bool ptr_ring_full(struct ptr_ring *r)
 {
-	barrier();
-	return __ptr_ring_full(r);
+	bool ret;
+
+	spin_lock(&r->producer_lock);
+	ret = __ptr_ring_full(r);
+	spin_unlock(&r->producer_lock);
+
+	return ret;
+}
+
+static inline bool ptr_ring_full_irq(struct ptr_ring *r)
+{
+	bool ret;
+
+	spin_lock_irq(&r->producer_lock);
+	ret = __ptr_ring_full(r);
+	spin_unlock_irq(&r->producer_lock);
+
+	return ret;
+}
+
+static inline bool ptr_ring_full_any(struct ptr_ring *r)
+{
+	unsigned long flags;
+	bool ret;
+
+	spin_lock_irqsave(&r->producer_lock, flags);
+	ret = __ptr_ring_full(r);
+	spin_unlock_irqrestore(&r->producer_lock, flags);
+
+	return ret;
+}
+
+static inline bool ptr_ring_full_bh(struct ptr_ring *r)
+{
+	bool ret;
+
+	spin_lock_bh(&r->producer_lock);
+	ret = __ptr_ring_full(r);
+	spin_unlock_bh(&r->producer_lock);
+
+	return ret;
 }
 
 /* Note: callers invoking this in a loop must use a compiler barrier,
- * for example cpu_relax().
+ * for example cpu_relax(). Callers must hold producer_lock.
  */
 static inline int __ptr_ring_produce(struct ptr_ring *r, void *ptr)
 {
-	if (__ptr_ring_full(r))
+	if (r->queue[r->producer])
 		return -ENOSPC;
 
 	r->queue[r->producer++] = ptr;
@@ -120,20 +159,68 @@ static inline int ptr_ring_produce_bh(struct ptr_ring *r, void *ptr)
 /* Note: callers invoking this in a loop must use a compiler barrier,
  * for example cpu_relax(). Callers must take consumer_lock
  * if they dereference the pointer - see e.g. PTR_RING_PEEK_CALL.
- * There's no need for a lock if pointer is merely tested - see e.g.
- * ptr_ring_empty.
+ * If ring is never resized, and if the pointer is merely
+ * tested, there's no need to take the lock - see e.g.  __ptr_ring_empty.
  */
 static inline void *__ptr_ring_peek(struct ptr_ring *r)
 {
 	return r->queue[r->consumer];
 }
 
-static inline bool ptr_ring_empty(struct ptr_ring *r)
+/* Note: callers invoking this in a loop must use a compiler barrier,
+ * for example cpu_relax(). Callers must take consumer_lock
+ * if the ring is ever resized - see e.g. ptr_ring_empty.
+ */
+static inline bool __ptr_ring_empty(struct ptr_ring *r)
 {
-	barrier();
 	return !__ptr_ring_peek(r);
 }
 
+static inline bool ptr_ring_empty(struct ptr_ring *r)
+{
+	bool ret;
+
+	spin_lock(&r->consumer_lock);
+	ret = __ptr_ring_empty(r);
+	spin_unlock(&r->consumer_lock);
+
+	return ret;
+}
+
+static inline bool ptr_ring_empty_irq(struct ptr_ring *r)
+{
+	bool ret;
+
+	spin_lock_irq(&r->consumer_lock);
+	ret = __ptr_ring_empty(r);
+	spin_unlock_irq(&r->consumer_lock);
+
+	return ret;
+}
+
+static inline bool ptr_ring_empty_any(struct ptr_ring *r)
+{
+	unsigned long flags;
+	bool ret;
+
+	spin_lock_irqsave(&r->consumer_lock, flags);
+	ret = __ptr_ring_empty(r);
+	spin_unlock_irqrestore(&r->consumer_lock, flags);
+
+	return ret;
+}
+
+static inline bool ptr_ring_empty_bh(struct ptr_ring *r)
+{
+	bool ret;
+
+	spin_lock_bh(&r->consumer_lock);
+	ret = __ptr_ring_empty(r);
+	spin_unlock_bh(&r->consumer_lock);
+
+	return ret;
+}
+
 /* Must only be called after __ptr_ring_peek returned !NULL */
 static inline void __ptr_ring_discard_one(struct ptr_ring *r)
 {
@@ -241,10 +328,14 @@ static inline void *ptr_ring_consume_bh(struct ptr_ring *r)
 	__PTR_RING_PEEK_CALL_v; \
 })
 
+static inline void **__ptr_ring_init_queue_alloc(int size, gfp_t gfp)
+{
+	return kzalloc(ALIGN(size * sizeof(void *), SMP_CACHE_BYTES), gfp);
+}
+
 static inline int ptr_ring_init(struct ptr_ring *r, int size, gfp_t gfp)
 {
-	r->queue = kzalloc(ALIGN(size * sizeof *(r->queue), SMP_CACHE_BYTES),
-			   gfp);
+	r->queue = __ptr_ring_init_queue_alloc(size, gfp);
 	if (!r->queue)
 		return -ENOMEM;
 
@@ -256,8 +347,46 @@ static inline int ptr_ring_init(struct ptr_ring *r, int size, gfp_t gfp)
 	return 0;
 }
 
-static inline void ptr_ring_cleanup(struct ptr_ring *r)
+static inline int ptr_ring_resize(struct ptr_ring *r, int size, gfp_t gfp,
+				  void (*destroy)(void *))
 {
+	unsigned long flags;
+	int producer = 0;
+	void **queue = __ptr_ring_init_queue_alloc(size, gfp);
+	void **old;
+	void *ptr;
+
+	if (!queue)
+		return -ENOMEM;
+
+	spin_lock_irqsave(&(r)->producer_lock, flags);
+
+	while ((ptr = ptr_ring_consume(r)))
+		if (producer < size)
+			queue[producer++] = ptr;
+		else if (destroy)
+			destroy(ptr);
+
+	r->size = size;
+	r->producer = producer;
+	r->consumer = 0;
+	old = r->queue;
+	r->queue = queue;
+
+	spin_unlock_irqrestore(&(r)->producer_lock, flags);
+
+	kfree(old);
+
+	return 0;
+}
+
+static inline void ptr_ring_cleanup(struct ptr_ring *r, void (*destroy)(void *))
+{
+	void *ptr;
+
+	if (destroy)
+		while ((ptr = ptr_ring_consume(r)))
+			destroy(ptr);
 	kfree(r->queue);
 }
 
-- 
MST