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Date:   Mon, 12 Dec 2022 18:36:02 -0800
From:   Stanislav Fomichev <>
        "Toke Høiland-Jørgensen" <>,
        David Ahern <>,
        Jakub Kicinski <>,
        Willem de Bruijn <>,
        Jesper Dangaard Brouer <>,
        Anatoly Burakov <>,
        Alexander Lobakin <>,
        Magnus Karlsson <>,
        Maryam Tahhan <>,,
Subject: [PATCH bpf-next v4 12/15] xsk: Add cb area to struct xdp_buff_xsk

From: Toke Høiland-Jørgensen <>

Add an area after the xdp_buff in struct xdp_buff_xsk that drivers can use
to stash extra information to use in metadata kfuncs. The maximum size of
24 bytes means the full xdp_buff_xsk structure will take up exactly two
cache lines (with the cb field spanning both). Also add a macro drivers can
use to check their own wrapping structs against the available size.

Cc: John Fastabend <>
Cc: David Ahern <>
Cc: Martin KaFai Lau <>
Cc: Jakub Kicinski <>
Cc: Willem de Bruijn <>
Cc: Jesper Dangaard Brouer <>
Cc: Anatoly Burakov <>
Cc: Alexander Lobakin <>
Cc: Magnus Karlsson <>
Cc: Maryam Tahhan <>
Suggested-by: Jakub Kicinski <>
Signed-off-by: Toke Høiland-Jørgensen <>
Signed-off-by: Stanislav Fomichev <>
 include/net/xsk_buff_pool.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/net/xsk_buff_pool.h b/include/net/xsk_buff_pool.h
index f787c3f524b0..3e952e569418 100644
--- a/include/net/xsk_buff_pool.h
+++ b/include/net/xsk_buff_pool.h
@@ -19,8 +19,11 @@ struct xdp_sock;
 struct device;
 struct page;
+#define XSK_PRIV_MAX 24
 struct xdp_buff_xsk {
 	struct xdp_buff xdp;
+	u8 cb[XSK_PRIV_MAX];
 	dma_addr_t dma;
 	dma_addr_t frame_dma;
 	struct xsk_buff_pool *pool;
@@ -28,6 +31,8 @@ struct xdp_buff_xsk {
 	struct list_head free_list_node;
+#define XSK_CHECK_PRIV_TYPE(t) BUILD_BUG_ON(sizeof(t) > offsetofend(struct xdp_buff_xsk, cb))
 struct xsk_dma_map {
 	dma_addr_t *dma_pages;
 	struct device *dev;

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