xsk: Add cb area to struct xdp_buff_xsk

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 <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Martin KaFai Lau <[email protected]>
Cc: Jakub Kicinski <[email protected]>
Cc: Willem de Bruijn <[email protected]>
Cc: Jesper Dangaard Brouer <[email protected]>
Cc: Anatoly Burakov <[email protected]>
Cc: Alexander Lobakin <[email protected]>
Cc: Magnus Karlsson <[email protected]>
Cc: Maryam Tahhan <[email protected]>
Cc: [email protected]
Cc: [email protected]
Suggested-by: Jakub Kicinski <[email protected]>
Signed-off-by: Toke Høiland-Jørgensen <[email protected]>
Signed-off-by: Stanislav Fomichev <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Martin KaFai Lau <[email protected]>

1 files changed, 5 insertions, 0 deletions

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;