Merge branch 'move-can-skb-headroom-content-to-skb-extensions'

Oliver Hartkopp says:

====================
move CAN skb headroom content to skb extensions

CAN bus related skbuffs (ETH_P_CAN/ETH_P_CANFD/ETH_P_CANXL) simply contain
CAN frame structs for CAN CC/FD/XL of skb->len length at skb->data. Those
CAN skbs do not have network/mac/transport headers nor other such
references for encapsulated protocols like ethernet/IP protocols.

To store data for CAN specific use-cases all CAN bus related skbuffs are
created with a 16 byte private skb headroom (struct can_skb_priv). Using
the skb headroom and accessing skb->head for this private data led to
several problems in the past likely due to "The struct can_skb_priv
business is highly unconventional for the networking stack." [1]

This patch set aims to remove the unconventional skb headroom usage for CAN
bus related skbuffs and use the common skb extensions instead.

[1] https://lore.kernel.org/linux-can/20260104074222.29e660ac@kernel.org/

- v1: https://patch.msgid.link/20260125201601.5018-1-socketcan@hartkopp.net
- v2: https://lore.kernel.org/linux-can/20260128-can-skb-ext-v2-0-fe64aa152c8a@pengutronix.de/
- v4: https://lore.kernel.org/netdev/20260128-can_skb_ext-v1-0-330f60fd5d7e@hartkopp.net/
- v5: https://patch.msgid.link/20260129-can_skb_ext-v5-0-21252fdc8900@hartkopp.net
- v6: https://patch.msgid.link/20260130-can_skb_ext-v6-0-8fceafab7f26@hartkopp.net
- v7: https://patch.msgid.link/20260131-can_skb_ext-v7-0-dd0f8f84a83d@hartkopp.net

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
====================

Link: https://patch.msgid.link/20260201-can_skb_ext-v8-0-3635d790fe8b@hartkopp.net
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

3 files changed, 15 insertions, 27 deletions

diff --git a/include/linux/can/core.h b/include/linux/can/core.h
index 5fb8d0e3f9c1..3287232e3cad 100644
--- a/include/linux/can/core.h
+++ b/include/linux/can/core.h
@@ -58,6 +58,7 @@ extern void can_rx_unregister(struct net *net, struct net_device *dev,
 			      void *data);
 
 extern int can_send(struct sk_buff *skb, int loop);
+void can_set_skb_uid(struct sk_buff *skb);
 void can_sock_destruct(struct sock *sk);
 
 #endif /* !_CAN_CORE_H */
diff --git a/include/linux/can/skb.h b/include/linux/can/skb.h
index 1abc25a8d144..a70a02967071 100644
--- a/include/linux/can/skb.h
+++ b/include/linux/can/skb.h
@@ -14,6 +14,7 @@
 #include <linux/types.h>
 #include <linux/skbuff.h>
 #include <linux/can.h>
+#include <net/can.h>
 #include <net/sock.h>
 
 void can_flush_echo_skb(struct net_device *dev);
@@ -37,37 +38,20 @@ struct sk_buff *alloc_can_err_skb(struct net_device *dev,
 				  struct can_frame **cf);
 bool can_dropped_invalid_skb(struct net_device *dev, struct sk_buff *skb);
 
-/*
- * The struct can_skb_priv is used to transport additional information along
- * with the stored struct can(fd)_frame that can not be contained in existing
- * struct sk_buff elements.
- * N.B. that this information must not be modified in cloned CAN sk_buffs.
- * To modify the CAN frame content or the struct can_skb_priv content
- * skb_copy() needs to be used instead of skb_clone().
- */
-
-/**
- * struct can_skb_priv - private additional data inside CAN sk_buffs
- * @ifindex:	ifindex of the first interface the CAN frame appeared on
- * @skbcnt:	atomic counter to have an unique id together with skb pointer
- * @frame_len:	length of CAN frame in data link layer
- * @cf:		align to the following CAN frame at skb->data
- */
-struct can_skb_priv {
-	int ifindex;
-	int skbcnt;
-	unsigned int frame_len;
-	struct can_frame cf[];
-};
-
-static inline struct can_skb_priv *can_skb_prv(struct sk_buff *skb)
+static inline struct can_skb_ext *can_skb_ext_add(struct sk_buff *skb)
 {
-	return (struct can_skb_priv *)(skb->head);
+	struct can_skb_ext *csx = skb_ext_add(skb, SKB_EXT_CAN);
+
+	/* skb_ext_add() returns uninitialized space */
+	if (csx)
+		csx->can_gw_hops = 0;
+
+	return csx;
 }
 
-static inline void can_skb_reserve(struct sk_buff *skb)
+static inline struct can_skb_ext *can_skb_ext_find(struct sk_buff *skb)
 {
-	skb_reserve(skb, sizeof(struct can_skb_priv));
+	return skb_ext_find(skb, SKB_EXT_CAN);
 }
 
 static inline void can_skb_set_owner(struct sk_buff *skb, struct sock *sk)
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 8b399ddf1b9b..ef56dc6318d3 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -4990,6 +4990,9 @@ enum skb_ext_id {
 #if IS_ENABLED(CONFIG_INET_PSP)
 	SKB_EXT_PSP,
 #endif
+#if IS_ENABLED(CONFIG_CAN)
+	SKB_EXT_CAN,
+#endif
 	SKB_EXT_NUM, /* must be last */
 };