[PATCH net-next v4 01/33] xdp: add frame size to xdp_buff

Jesper Dangaard Brouer
2020-05-14T10:49:21Z

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>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
include/net/xdp.h | 13 +++++++++++++
1 file changed, 13 insertions(+)

diff --git a/include/net/xdp.h b/include/net/xdp.h
index 3cc6d5d84aa4..a764af4ae0ea 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;