xsk: include XDP meta data in AF_XDP frames

Previously, the AF_XDP (XDP_DRV/XDP_SKB copy-mode) ingress logic did
not include XDP meta data in the data buffers copied out to the user
application.

In this commit, we check if meta data is available, and if so, it is
prepended to the frame.

Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

net/xdp/xsk.c

@@ -55,20 +55,30 @@ EXPORT_SYMBOL(xsk_umem_discard_addr);
 
 static int __xsk_rcv(struct xdp_sock *xs, struct xdp_buff *xdp, u32 len)
 {
-	void *buffer;
+	void *to_buf, *from_buf;
+	u32 metalen;
 	u64 addr;
 	int err;
 
 	if (!xskq_peek_addr(xs->umem->fq, &addr) ||
-	    len > xs->umem->chunk_size_nohr) {
+	    len > xs->umem->chunk_size_nohr - XDP_PACKET_HEADROOM) {
 		xs->rx_dropped++;
 		return -ENOSPC;
 	}
 
 	addr += xs->umem->headroom;
 
-	buffer = xdp_umem_get_data(xs->umem, addr);
-	memcpy(buffer, xdp->data, len);
+	if (unlikely(xdp_data_meta_unsupported(xdp))) {
+		from_buf = xdp->data;
+		metalen = 0;
+	} else {
+		from_buf = xdp->data_meta;
+		metalen = xdp->data - xdp->data_meta;
+	}
+
+	to_buf = xdp_umem_get_data(xs->umem, addr);
+	memcpy(to_buf, from_buf, len + metalen);
+	addr += metalen;
 	err = xskq_produce_batch_desc(xs->rx, addr, len);
 	if (!err) {
 		xskq_discard_addr(xs->umem->fq);
@@ -111,6 +121,7 @@ void xsk_flush(struct xdp_sock *xs)
 
 int xsk_generic_rcv(struct xdp_sock *xs, struct xdp_buff *xdp)
 {
+	u32 metalen = xdp->data - xdp->data_meta;
 	u32 len = xdp->data_end - xdp->data;
 	void *buffer;
 	u64 addr;
@@ -120,15 +131,16 @@ int xsk_generic_rcv(struct xdp_sock *xs, struct xdp_buff *xdp)
 		return -EINVAL;
 
 	if (!xskq_peek_addr(xs->umem->fq, &addr) ||
-	    len > xs->umem->chunk_size_nohr) {
+	    len > xs->umem->chunk_size_nohr - XDP_PACKET_HEADROOM) {
 		xs->rx_dropped++;
 		return -ENOSPC;
 	}
 
 	addr += xs->umem->headroom;
 
 	buffer = xdp_umem_get_data(xs->umem, addr);
-	memcpy(buffer, xdp->data, len);
+	memcpy(buffer, xdp->data_meta, len + metalen);
+	addr += metalen;
 	err = xskq_produce_batch_desc(xs->rx, addr, len);
 	if (!err) {
 		xskq_discard_addr(xs->umem->fq);