[SRU][F:linux-bluefield][PATCH 01/21] xdp: Add frame size to xdp_buff

Bodong Wang bodong at nvidia.com
Mon Jul 5 15:39:39 UTC 2021

From: Jesper Dangaard Brouer <brouer at redhat.com>

BugLink: https://bugs.launchpad.net/bugs/1934499

XDP have evolved to support several frame sizes, but xdp_buff was not
updated with this information. The frame size (frame_sz) member of
xdp_buff is introduced to know the real size of the memory the frame is
delivered in.

When introducing this also make it clear that some tailroom is
reserved/required when creating SKBs using build_skb().

It would also have been an option to introduce a pointer to
data_hard_end (with reserved offset). The advantage with frame_sz is
that (like rxq) drivers only need to setup/assign this value once per
NAPI cycle. Due to XDP-generic (and some drivers) it's not possible to
store frame_sz inside xdp_rxq_info, because it's varies per packet as it
can be based/depend on packet length.

V2: nitpick: deduct -> deduce

Signed-off-by: Jesper Dangaard Brouer <brouer at redhat.com>
Signed-off-by: Alexei Starovoitov <ast at kernel.org>
Acked-by: Toke Høiland-Jørgensen <toke at redhat.com>
Link: https://lore.kernel.org/bpf/158945334261.97035.555255657490688547.stgit@firesoul
(cherry picked from commit f95f0f95cfb7f180ed7571d4915432d5098df7ec)
Signed-off-by: Maxim Mikityanskiy <maximmi at nvidia.com>
Reviewed-by: Moshe Shemesh <moshe at nvidia.com>
Signed-off-by: Bodong Wang <bodong at nvidia.com>
 include/net/xdp.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/include/net/xdp.h b/include/net/xdp.h
index 40c6d33..741f63e 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h
@@ -6,6 +6,8 @@
 #ifndef __LINUX_NET_XDP_H__
 #define __LINUX_NET_XDP_H__
+#include <linux/skbuff.h> /* skb_shared_info */
  * DOC: XDP RX-queue information
@@ -70,8 +72,19 @@ struct xdp_buff {
 	void *data_hard_start;
 	unsigned long handle;
 	struct xdp_rxq_info *rxq;
+	u32 frame_sz; /* frame size to deduce data_hard_end/reserved tailroom*/
+/* Reserve memory area at end-of data area.
+ *
+ * This macro reserves tailroom in the XDP buffer by limiting the
+ * XDP/BPF data access to data_hard_end.  Notice same area (and size)
+ * is used for XDP_PASS, when constructing the SKB via build_skb().
+ */
+#define xdp_data_hard_end(xdp)				\
+	((xdp)->data_hard_start + (xdp)->frame_sz -	\
+	 SKB_DATA_ALIGN(sizeof(struct skb_shared_info)))
 struct xdp_frame {
 	void *data;
 	u16 len;

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