linux-kernel - [PATCH net-next v7 3/9] tun/tap: add ptr_ring consume helper with netdev queue wakeup

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Message-ID: <20260107210448.37851-4-simon.schippers@tu-dortmund.de>
Date: Wed,  7 Jan 2026 22:04:42 +0100
From: Simon Schippers <simon.schippers@...dortmund.de>
To: willemdebruijn.kernel@...il.com, jasowang@...hat.com,
        andrew+netdev@...n.ch, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com, mst@...hat.com,
        eperezma@...hat.com, leiyang@...hat.com, stephen@...workplumber.org,
        jon@...anix.com, tim.gebauer@...dortmund.de,
        simon.schippers@...dortmund.de, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        virtualization@...ts.linux.dev
Subject: [PATCH net-next v7 3/9] tun/tap: add ptr_ring consume helper with netdev queue wakeup

Introduce {tun,tap}_ring_consume() helpers that wrap __ptr_ring_consume()
and wake the corresponding netdev subqueue when consuming an entry frees
space in the underlying ptr_ring.

Stopping of the netdev queue when the ptr_ring is full will be introduced
in an upcoming commit.

Co-developed-by: Tim Gebauer <tim.gebauer@...dortmund.de>
Signed-off-by: Tim Gebauer <tim.gebauer@...dortmund.de>
Signed-off-by: Simon Schippers <simon.schippers@...dortmund.de>
---
 drivers/net/tap.c | 23 ++++++++++++++++++++++-
 drivers/net/tun.c | 25 +++++++++++++++++++++++--
 2 files changed, 45 insertions(+), 3 deletions(-)

diff --git a/drivers/net/tap.c b/drivers/net/tap.c
index 1197f245e873..2442cf7ac385 100644
--- a/drivers/net/tap.c
+++ b/drivers/net/tap.c
@@ -753,6 +753,27 @@ static ssize_t tap_put_user(struct tap_queue *q,
 	return ret ? ret : total;
 }
 
+static void *tap_ring_consume(struct tap_queue *q)
+{
+	struct ptr_ring *ring = &q->ring;
+	struct net_device *dev;
+	void *ptr;
+
+	spin_lock(&ring->consumer_lock);
+
+	ptr = __ptr_ring_consume(ring);
+	if (unlikely(ptr && __ptr_ring_consume_created_space(ring, 1))) {
+		rcu_read_lock();
+		dev = rcu_dereference(q->tap)->dev;
+		netif_wake_subqueue(dev, q->queue_index);
+		rcu_read_unlock();
+	}
+
+	spin_unlock(&ring->consumer_lock);
+
+	return ptr;
+}
+
 static ssize_t tap_do_read(struct tap_queue *q,
 			   struct iov_iter *to,
 			   int noblock, struct sk_buff *skb)
@@ -774,7 +795,7 @@ static ssize_t tap_do_read(struct tap_queue *q,
 					TASK_INTERRUPTIBLE);
 
 		/* Read frames from the queue */
-		skb = ptr_ring_consume(&q->ring);
+		skb = tap_ring_consume(q);
 		if (skb)
 			break;
 		if (noblock) {
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 8192740357a0..7148f9a844a4 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -2113,13 +2113,34 @@ static ssize_t tun_put_user(struct tun_struct *tun,
 	return total;
 }
 
+static void *tun_ring_consume(struct tun_file *tfile)
+{
+	struct ptr_ring *ring = &tfile->tx_ring;
+	struct net_device *dev;
+	void *ptr;
+
+	spin_lock(&ring->consumer_lock);
+
+	ptr = __ptr_ring_consume(ring);
+	if (unlikely(ptr && __ptr_ring_consume_created_space(ring, 1))) {
+		rcu_read_lock();
+		dev = rcu_dereference(tfile->tun)->dev;
+		netif_wake_subqueue(dev, tfile->queue_index);
+		rcu_read_unlock();
+	}
+
+	spin_unlock(&ring->consumer_lock);
+
+	return ptr;
+}
+
 static void *tun_ring_recv(struct tun_file *tfile, int noblock, int *err)
 {
 	DECLARE_WAITQUEUE(wait, current);
 	void *ptr = NULL;
 	int error = 0;
 
-	ptr = ptr_ring_consume(&tfile->tx_ring);
+	ptr = tun_ring_consume(tfile);
 	if (ptr)
 		goto out;
 	if (noblock) {
@@ -2131,7 +2152,7 @@ static void *tun_ring_recv(struct tun_file *tfile, int noblock, int *err)
 
 	while (1) {
 		set_current_state(TASK_INTERRUPTIBLE);
-		ptr = ptr_ring_consume(&tfile->tx_ring);
+		ptr = tun_ring_consume(tfile);
 		if (ptr)
 			break;
 		if (signal_pending(current)) {
-- 
2.43.0