bpf: xdp: Allow head adjustment in XDP prog

This patch allows XDP prog to extend/remove the packet
data at the head (like adding or removing header).  It is
done by adding a new XDP helper bpf_xdp_adjust_head().

It also renames bpf_helper_changes_skb_data() to
bpf_helper_changes_pkt_data() to better reflect
that XDP prog does not work on skb.

This patch adds one "xdp_adjust_head" bit to bpf_prog for the
XDP-capable driver to check if the XDP prog requires
bpf_xdp_adjust_head() support.  The driver can then decide
to error out during XDP_SETUP_PROG.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.r.fastabend@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlx4/en_netdev.c

@@ -2686,6 +2686,11 @@ static int mlx4_xdp_set(struct net_device *dev, struct bpf_prog *prog)
 	int err;
 	int i;
 
+	if (prog && prog->xdp_adjust_head) {
+		en_err(priv, "Does not support bpf_xdp_adjust_head()\n");
+		return -EOPNOTSUPP;
+	}
+
 	xdp_ring_num = prog ? priv->rx_ring_num : 0;
 
 	/* No need to reconfigure buffers when simply swapping the

drivers/net/ethernet/mellanox/mlx5/core/en_main.c

@@ -3183,6 +3183,11 @@ static int mlx5e_xdp_set(struct net_device *netdev, struct bpf_prog *prog)
 	bool reset, was_opened;
 	int i;
 
+	if (prog && prog->xdp_adjust_head) {
+		netdev_err(netdev, "Does not support bpf_xdp_adjust_head()\n");
+		return -EOPNOTSUPP;
+	}
+
 	mutex_lock(&priv->state_lock);
 
 	if ((netdev->features & NETIF_F_LRO) && prog) {

drivers/net/ethernet/netronome/nfp/nfp_net_common.c

@@ -2946,6 +2946,10 @@ static int nfp_net_xdp_setup(struct nfp_net *nn, struct bpf_prog *prog)
 	};
 	int err;
 
+	if (prog && prog->xdp_adjust_head) {
+		nn_err(nn, "Does not support bpf_xdp_adjust_head()\n");
+		return -EOPNOTSUPP;
+	}
 	if (!prog && !nn->xdp_prog)
 		return 0;
 	if (prog && nn->xdp_prog) {

drivers/net/ethernet/qlogic/qede/qede_main.c

@@ -2507,6 +2507,11 @@ static int qede_xdp_set(struct qede_dev *edev, struct bpf_prog *prog)
 {
 	struct qede_reload_args args;
 
+	if (prog && prog->xdp_adjust_head) {
+		DP_ERR(edev, "Does not support bpf_xdp_adjust_head()\n");
+		return -EOPNOTSUPP;
+	}
+
 	/* If we're called, there was already a bpf reference increment */
 	args.func = &qede_xdp_reload_func;
 	args.u.new_prog = prog;