xdp: add XDP extension to skb

This patch adds a new skb extension for XDP representing the number of
cq descriptors and a linked list of umem addresses.

This is going to be used from the xsk skb destructor to put the umem
addresses onto pool's completion queue.

Signed-off-by: Fernando Fernandez Mancera <[email protected]>

Author: Fernando Fernandez Mancera

include/linux/skbuff.h

@@ -4910,6 +4910,9 @@ enum skb_ext_id {
 #endif
 #if IS_ENABLED(CONFIG_INET_PSP)
 	SKB_EXT_PSP,
+#endif
+#if IS_ENABLED(CONFIG_XDP_SOCKETS)
+	SKB_EXT_XDP,
 #endif
 	SKB_EXT_NUM, /* must be last */
 };

include/net/xdp_sock.h

@@ -120,6 +120,11 @@ struct xsk_tx_metadata_ops {
 	void	(*tmo_request_launch_time)(u64 launch_time, void *priv);
 };
 
+struct xdp_skb_ext {
+	u32 num_descs;
+	struct list_head addrs_list;
+};
+
 #ifdef CONFIG_XDP_SOCKETS
 
 int xsk_generic_rcv(struct xdp_sock *xs, struct xdp_buff *xdp);

net/core/skbuff.c

@@ -81,6 +81,7 @@
 #include <net/page_pool/helpers.h>
 #include <net/psp/types.h>
 #include <net/dropreason.h>
+#include <net/xdp_sock.h>
 
 #include <linux/uaccess.h>
 #include <trace/events/skb.h>
@@ -5066,6 +5067,9 @@ static const u8 skb_ext_type_len[] = {
 #if IS_ENABLED(CONFIG_INET_PSP)
 	[SKB_EXT_PSP] = SKB_EXT_CHUNKSIZEOF(struct psp_skb_ext),
 #endif
+#if IS_ENABLED(CONFIG_XDP_SOCKETS)
+	[SKB_EXT_XDP] = SKB_EXT_CHUNKSIZEOF(struct xdp_skb_ext),
+#endif
 };
 
 static __always_inline unsigned int skb_ext_total_length(void)

net/xdp/Kconfig

@@ -2,6 +2,7 @@
 config XDP_SOCKETS
 	bool "XDP sockets"
 	depends on BPF_SYSCALL
+	select SKB_EXTENSIONS
 	default n
 	help
 	  XDP sockets allows a channel between XDP programs and