Introduce convert_to_xdp_buff utility routine to initialize xdp_buff
fields from xdp_frames ones. Rely on convert_to_xdp_buff in veth xdp
code

Suggested-by: Jesper Dangaard Brouer <redacted>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
Changes since v1:
- rely on frame->data pointer to compute xdp->data_hard_start one
---
 drivers/net/veth.c |  6 +-----
 include/net/xdp.h  | 10 ++++++++++
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index b586d2fa5551..9f91e79b7823 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c

@@ -575,11 +575,7 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq,
 		struct xdp_buff xdp;
 		u32 act;
 
-		xdp.data_hard_start = hard_start;
-		xdp.data = frame->data;
-		xdp.data_end = frame->data + frame->len;
-		xdp.data_meta = frame->data - frame->metasize;
-		xdp.frame_sz = frame->frame_sz;
+		convert_to_xdp_buff(frame, &xdp);
 		xdp.rxq = &rq->xdp_rxq;
 
 		act = bpf_prog_run_xdp(xdp_prog, &xdp);

diff --git a/include/net/xdp.h b/include/net/xdp.h
index 90f11760bd12..df99d5d267b2 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h

@@ -106,6 +106,16 @@ void xdp_warn(const char *msg, const char *func, const int line);
 
 struct xdp_frame *xdp_convert_zc_to_xdp_frame(struct xdp_buff *xdp);
 
+static inline
+void convert_to_xdp_buff(struct xdp_frame *frame, struct xdp_buff *xdp)
+{
+	xdp->data_hard_start = frame->data - frame->headroom - sizeof(*frame);
+	xdp->data = frame->data;
+	xdp->data_end = frame->data + frame->len;
+	xdp->data_meta = frame->data - frame->metasize;
+	xdp->frame_sz = frame->frame_sz;
+}