[PATCH wireless-next 01/18] net: skbuff: Add SKB extension support to wireless drivers

[Pooventhiran G]

IEEE P802.11bn/D2.0, Aug 2026, subclause 37.16, defines Seamless
Mobility Domain (SMD) BSS Transition, in which a station roams between
two AP MLDs within an SMD across two phases: Preparation and Execution.
During these phases, the receiving AP driver processes a query frame and
must carry the station's roaming context - per-TID sequence numbers in
downlink (DL) and uplink (UL) directions, packet number in DL and
per-TID packet numbers in UL, and per-TID BlockAck session parameters in
DL and UL, plus a variable-length driver context - up through mac80211
and nl80211 to userspace, which uses it to complete the transition.

This context does not fit in skb->cb (48 bytes). Carrying it separately,
outside the SKB, breaks when the SKB is cloned through the RX path because
the context lifetime is no longer tied to the frame; the driver would need
independent state correlated with the SKB at nl80211 encode time, adding
error-prone lifecycle management. SKB extensions avoid these problems: they
are reference-counted, copy-on-write safe, and freed automatically with the
SKB.

Add a new skbuff_wireless.h with a typed union structured to accommodate
future wireless extension types, carrying the SMD roaming context as its
first payload.

Signed-off-by: Pooventhiran G <pooventhiran.g@xxxxxxxxxxxxxxxx>
---
 include/linux/skbuff.h          |  3 +++
 include/linux/skbuff_wireless.h | 55 +++++++++++++++++++++++++++++++++++++++++
 net/core/skbuff.c               | 55 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 113 insertions(+)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 421f6fc45451..fb686024e97d 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -5061,6 +5061,9 @@ enum skb_ext_id {
 #endif
 #if IS_ENABLED(CONFIG_CAN)
 	SKB_EXT_CAN,
+#endif
+#if IS_ENABLED(CONFIG_WIRELESS)
+	SKB_EXT_WIRELESS,
 #endif
 	SKB_EXT_NUM, /* must be last */
 };
diff --git a/include/linux/skbuff_wireless.h b/include/linux/skbuff_wireless.h
new file mode 100644
index 000000000000..2cb04bff061c
--- /dev/null
+++ b/include/linux/skbuff_wireless.h
@@ -0,0 +1,55 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * IEEE 802.11 WLAN skb_ext definitions
+ *
+ * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
+ */
+
+#ifndef LINUX_SKB_WIRELESS_H
+#define LINUX_SKB_WIRELESS_H
+
+#include <linux/types.h>
+#include <linux/refcount.h>
+
+/**
+ * enum wireless_skb_ext_type - type of data in wireless_skb_ext
+ * @WIRELESS_SKB_EXT_INVALID: uninitialized state
+ * @WIRELESS_SKB_EXT_UHR_SMD: payload is @uhr_smd_ctx
+ */
+enum wireless_skb_ext_type {
+	WIRELESS_SKB_EXT_INVALID,
+	WIRELESS_SKB_EXT_UHR_SMD,
+};
+
+/**
+ * struct wireless_skb_ext_smd_ctx - UHR SMD roaming context container in
+ *	SKB extensions
+ * @refcnt: reference count; one count per distinct skb_ext block that holds
+ *	this pointer. Plain skb_clone() shares the same skb_ext block and
+ *	does not increment this counter. Only skb_ext_maybe_cow() increments
+ *	this counter, when a COW produces a second independent ext block copy.
+ * @smd_ctx: pointer to the IEEE P802.11bn UHR SMD roaming context;
+ *	must be a kmalloc-ed buffer, freed together with this container.
+ */
+struct wireless_skb_ext_smd_ctx {
+	refcount_t refcnt;
+	void *smd_ctx;
+};
+
+/**
+ * struct wireless_skb_ext - SKB extension data for wireless module use
+ *
+ * Carried as an skb extension (SKB_EXT_WIRELESS). The union is reserved
+ * for future wireless extension types; only one member is active per skb.
+ *
+ * @type: type of data
+ * @uhr_smd_ctx: pointer to the UHR SMD context container
+ */
+struct wireless_skb_ext {
+	enum wireless_skb_ext_type type;
+	union {
+		struct wireless_skb_ext_smd_ctx *uhr_smd_ctx;
+	};
+};
+
+#endif /* LINUX_SKB_WIRELESS_H */
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index ab195b99c853..f28ab7c3c888 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -93,6 +93,10 @@
 #include <linux/indirect_call_wrapper.h>
 #include <linux/textsearch.h>
 
+#if IS_ENABLED(CONFIG_WIRELESS)
+#include <linux/skbuff_wireless.h>
+#endif
+
 #include "dev.h"
 #include "devmem.h"
 #include "net-sysfs.h"
@@ -5169,6 +5173,9 @@ static const u8 skb_ext_type_len[] = {
 #if IS_ENABLED(CONFIG_CAN)
 	[SKB_EXT_CAN] = SKB_EXT_CHUNKSIZEOF(struct can_skb_ext),
 #endif
+#if IS_ENABLED(CONFIG_WIRELESS)
+	[SKB_EXT_WIRELESS] = SKB_EXT_CHUNKSIZEOF(struct wireless_skb_ext),
+#endif
 };
 
 static __always_inline __no_profile unsigned int skb_ext_total_length(void)
@@ -7152,6 +7159,16 @@ static struct skb_ext *skb_ext_maybe_cow(struct skb_ext *old,
 		if (flow->key)
 			refcount_inc(&flow->key->refs);
 	}
+#endif
+#if IS_ENABLED(CONFIG_WIRELESS)
+	if (old_active & (1 << SKB_EXT_WIRELESS)) {
+		struct wireless_skb_ext *wifi =
+			skb_ext_get_ptr(old, SKB_EXT_WIRELESS);
+
+		if (wifi->type == WIRELESS_SKB_EXT_UHR_SMD &&
+		    wifi->uhr_smd_ctx)
+			refcount_inc(&wifi->uhr_smd_ctx->refcnt);
+	}
 #endif
 	__skb_ext_put(old);
 	return new;
@@ -7256,6 +7273,36 @@ static void skb_ext_put_mctp(struct mctp_flow *flow)
 }
 #endif
 
+#if IS_ENABLED(CONFIG_WIRELESS)
+static void skb_ext_put_wireless(struct wireless_skb_ext *wifi)
+{
+	switch (wifi->type) {
+	case WIRELESS_SKB_EXT_UHR_SMD:
+		if (!wifi->uhr_smd_ctx)
+			break;
+
+		if (refcount_dec_and_test(&wifi->uhr_smd_ctx->refcnt)) {
+			kfree(wifi->uhr_smd_ctx->smd_ctx);
+			kfree(wifi->uhr_smd_ctx);
+		}
+
+		/*
+		 * __skb_ext_del clears active_extensions but not ext->offset[],
+		 * so __skb_ext_put will call skb_ext_put_wireless again;
+		 * mark NULL regardless to avoid double free in __skb_ext_put.
+		 */
+		wifi->uhr_smd_ctx = NULL;
+		break;
+	case WIRELESS_SKB_EXT_INVALID:
+		/* data not yet set */
+		break;
+	default:
+		WARN_ONCE(1, "unknown wireless skb extension type=%u\n",
+			  wifi->type);
+	}
+}
+#endif
+
 void __skb_ext_del(struct sk_buff *skb, enum skb_ext_id id)
 {
 	struct skb_ext *ext = skb->extensions;
@@ -7278,6 +7325,10 @@ void __skb_ext_del(struct sk_buff *skb, enum skb_ext_id id)
 	if (id == SKB_EXT_MCTP)
 		skb_ext_put_mctp(skb_ext_get_ptr(ext, SKB_EXT_MCTP));
 #endif
+#if IS_ENABLED(CONFIG_WIRELESS)
+	if (id == SKB_EXT_WIRELESS)
+		skb_ext_put_wireless(skb_ext_get_ptr(ext, SKB_EXT_WIRELESS));
+#endif
 }
 EXPORT_SYMBOL(__skb_ext_del);
 
@@ -7300,6 +7351,10 @@ void __skb_ext_put(struct skb_ext *ext)
 	if (__skb_ext_exist(ext, SKB_EXT_MCTP))
 		skb_ext_put_mctp(skb_ext_get_ptr(ext, SKB_EXT_MCTP));
 #endif
+#if IS_ENABLED(CONFIG_WIRELESS)
+	if (__skb_ext_exist(ext, SKB_EXT_WIRELESS))
+		skb_ext_put_wireless(skb_ext_get_ptr(ext, SKB_EXT_WIRELESS));
+#endif
 
 	kmem_cache_free(skbuff_ext_cache, ext);
 }

-- 
2.34.1