netdev - [PATCH net-next 01/10] net: Document skb_metadata

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Message-Id: <20260110-skb-meta-fixup-skb_metadata_set-calls-v1-1-1047878ed1b0@cloudflare.com>
Date: Sat, 10 Jan 2026 22:05:15 +0100
From: Jakub Sitnicki <jakub@...udflare.com>
To: netdev@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
 Michael Chan <michael.chan@...adcom.com>, 
 Pavan Chebbi <pavan.chebbi@...adcom.com>, 
 Andrew Lunn <andrew+netdev@...n.ch>, 
 Tony Nguyen <anthony.l.nguyen@...el.com>, 
 Przemek Kitszel <przemyslaw.kitszel@...el.com>, 
 Saeed Mahameed <saeedm@...dia.com>, Leon Romanovsky <leon@...nel.org>, 
 Tariq Toukan <tariqt@...dia.com>, Mark Bloch <mbloch@...dia.com>, 
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
 Jesper Dangaard Brouer <hawk@...nel.org>, 
 John Fastabend <john.fastabend@...il.com>, 
 Stanislav Fomichev <sdf@...ichev.me>, intel-wired-lan@...ts.osuosl.org, 
 bpf@...r.kernel.org, kernel-team@...udflare.com
Subject: [PATCH net-next 01/10] net: Document skb_metadata_set contract
 with the drivers

Prepare to copy XDP metadata into an skb extension chunk. To access the
metadata contents, we need to know where it is located. Document the
expectation - skb->data must point right past the metadata when
skb_metadata_set gets called.

Signed-off-by: Jakub Sitnicki <jakub@...udflare.com>
---
 include/linux/skbuff.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 86737076101d..df001283076f 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -4554,6 +4554,13 @@ static inline bool skb_metadata_differs(const struct sk_buff *skb_a,
 	       true : __skb_metadata_differs(skb_a, skb_b, len_a);
 }

+/**
+ * skb_metadata_set - Record packet metadata length.
+ * @skb: packet carrying the metadata
+ * @meta_len: number of bytes of metadata preceding skb->data
+ *
+ * Must be called when skb->data already points past the metadata area.
+ */
 static inline void skb_metadata_set(struct sk_buff *skb, u8 meta_len)
 {
 	skb_shinfo(skb)->meta_len = meta_len;

-- 
2.43.0