Commit f95f0f95 authored May 14, 2020 by Jesper Dangaard Brouer Committed by Alexei Starovoitov May 14, 2020

xdp: Add frame size to xdp_buff



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@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/158945334261.97035.555255657490688547.stgit@firesoul

parent d00f26b6

include/net/xdp.h

+13 −0

Original line number	Diff line number	Diff line
		@@ -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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