[PATCH RFC net-next v4 02/14] xsk: extend xsk_build_skb() to support passing an already allocated skb

Jason Xing
2026-04-15T08:27:19Z

To avoid reinvent the wheel, the patch provides a way to let batch
feature 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 <kernelxing@tencent.com>
---
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 965cab9a0465..90c709fd1239 100644
--- a/include/net/xdp_sock.h
+++ b/include/net/xdp_sock.h
@@ -133,6 +133,9 @@ int xsk_generic_rcv(struct xdp_sock *xs, struct xdp_buff *xdp);
int __xsk_map_redirect(struct xdp_sock *xs, struct xdp_buff *xdp);
void __xsk_map_flush(struct list_head *flush_list);
INDIRECT_CALLABLE_DECLARE(void xsk_destruct_skb(struct sk_buff *));
+struct sk_buff *xsk_build_skb(struct xdp_sock *xs,
+ struct sk_buff *allocated_skb,
+ struct xdp_desc *desc);

/**
* xsk_tx_metadata_to_compl - Save enough relevant metadata information
diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index 6122db8606fe..ecd5b9c424b8 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -718,6 +718,7 @@ 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;
@@ -734,7 +735,10 @@ 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);

@@ -799,15 +803,16 @@ 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;
@@ -822,8 +827,12 @@ 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;

@@ -943,7 +952,7 @@ 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