Subject: [PATCH net-next v3 2/9] xsk: extend xsk_build_skb() to support passing an already allocated skb

From: Jason Xing <[email-masked]>
Date: Tue, 21 Oct 2025 21:12:02 +0800

From: Jason Xing <[email-masked]>

To avoid reinvent the wheel, the patch provides a way to let batch
feature to reuse xsk_build_skb() as the rest process of the whole
initialization just after the skb is allocated.

The original xsk_build_skb() itself allocates a new skb by calling
sock_alloc_send_skb whether in copy mode or zerocopy mode. Add a new
parameter allocated skb to let other callers to pass an already
allocated skb to support later xmit batch feature. It replaces the
previous allocation of memory function with a bulk one.

Signed-off-by: Jason Xing <[email-masked]>
---
 include/net/xdp_sock.h |  3 +++
 net/xdp/xsk.c          | 23 ++++++++++++++++-------
 2 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/include/net/xdp_sock.h b/include/net/xdp_sock.h
index f33f1e7dcea2..8944f4782eb6 100644
--- a/include/net/xdp_sock.h
+++ b/include/net/xdp_sock.h
@@ -127,6 +127,9 @@ struct xsk_tx_metadata_ops {
 	void	(*tmo_request_launch_time)(u64 launch_time, void *priv);
 };
 
+struct sk_buff *xsk_build_skb(struct xdp_sock *xs,
+			      struct sk_buff *allocated_skb,
+			      struct xdp_desc *desc);
 #ifdef CONFIG_XDP_SOCKETS
 
 int xsk_generic_rcv(struct xdp_sock *xs, struct xdp_buff *xdp);
diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index ace91800c447..f9458347ff7b 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -697,6 +697,7 @@ static int xsk_skb_metadata(struct sk_buff *skb, void *buffer,
 }
 
 static struct sk_buff *xsk_build_skb_zerocopy(struct xdp_sock *xs,
+					      struct sk_buff *allocated_skb,
 					      struct xdp_desc *desc)
 {
 	struct xsk_buff_pool *pool = xs->pool;
@@ -714,7 +715,10 @@ static struct sk_buff *xsk_build_skb_zerocopy(struct xdp_sock *xs,
 	if (!skb) {
 		hr = max(NET_SKB_PAD, L1_CACHE_ALIGN(xs->dev->needed_headroom));
 
-		skb = sock_alloc_send_skb(&xs->sk, hr, 1, &err);
+		if (!allocated_skb)
+			skb = sock_alloc_send_skb(&xs->sk, hr, 1, &err);
+		else
+			skb = allocated_skb;
 		if (unlikely(!skb))
 			return ERR_PTR(err);
 
@@ -769,15 +773,16 @@ static struct sk_buff *xsk_build_skb_zerocopy(struct xdp_sock *xs,
 	return skb;
 }
 
-static struct sk_buff *xsk_build_skb(struct xdp_sock *xs,
-				     struct xdp_desc *desc)
+struct sk_buff *xsk_build_skb(struct xdp_sock *xs,
+			      struct sk_buff *allocated_skb,
+			      struct xdp_desc *desc)
 {
 	struct net_device *dev = xs->dev;
 	struct sk_buff *skb = xs->skb;
 	int err;
 
 	if (dev->priv_flags & IFF_TX_SKB_NO_LINEAR) {
-		skb = xsk_build_skb_zerocopy(xs, desc);
+		skb = xsk_build_skb_zerocopy(xs, allocated_skb, desc);
 		if (IS_ERR(skb)) {
 			err = PTR_ERR(skb);
 			skb = NULL;
@@ -792,8 +797,12 @@ static struct sk_buff *xsk_build_skb(struct xdp_sock *xs,
 
 		if (!skb) {
 			hr = max(NET_SKB_PAD, L1_CACHE_ALIGN(dev->needed_headroom));
-			tr = dev->needed_tailroom;
-			skb = sock_alloc_send_skb(&xs->sk, hr + len + tr, 1, &err);
+			if (!allocated_skb) {
+				tr = dev->needed_tailroom;
+				skb = sock_alloc_send_skb(&xs->sk, hr + len + tr, 1, &err);
+			} else {
+				skb = allocated_skb;
+			}
 			if (unlikely(!skb))
 				goto free_err;
 
@@ -906,7 +915,7 @@ static int __xsk_generic_xmit(struct sock *sk)
 			goto out;
 		}
 
-		skb = xsk_build_skb(xs, &desc);
+		skb = xsk_build_skb(xs, NULL, &desc);
 		if (IS_ERR(skb)) {
 			err = PTR_ERR(skb);
 			if (err != -EOVERFLOW)
-- 
2.41.3