bpf: add helpers to access tunnel metadata

Introduce helpers to let eBPF programs attached to TC manipulate tunnel metadata:
bpf_skb_[gs]et_tunnel_key(skb, key, size, flags)
skb: pointer to skb
key: pointer to 'struct bpf_tunnel_key'
size: size of 'struct bpf_tunnel_key'
flags: room for future extensions

First eBPF program that uses these helpers will allocate per_cpu
metadata_dst structures that will be used on TX.
On RX metadata_dst is allocated by tunnel driver.

Typical usage for TX:
struct bpf_tunnel_key tkey;
... populate tkey ...
bpf_skb_set_tunnel_key(skb, &tkey, sizeof(tkey), 0);
bpf_clone_redirect(skb, vxlan_dev_ifindex, 0);

RX:
struct bpf_tunnel_key tkey = {};
bpf_skb_get_tunnel_key(skb, &tkey, sizeof(tkey), 0);
... lookup or redirect based on tkey ...

'struct bpf_tunnel_key' will be extended in the future by adding
elements to the end and the 'size' argument will indicate which fields
are populated, thereby keeping backwards compatibility.
The 'flags' argument may be used as well when the 'size' is not enough or
to indicate completely different layout of bpf_tunnel_key.

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 17 insertions, 0 deletions

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 2f6c83d714e9..bc0d27d3fbdd 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -258,6 +258,18 @@ enum bpf_func_id {
 	BPF_FUNC_get_cgroup_classid,
 	BPF_FUNC_skb_vlan_push, /* bpf_skb_vlan_push(skb, vlan_proto, vlan_tci) */
 	BPF_FUNC_skb_vlan_pop,  /* bpf_skb_vlan_pop(skb) */
+
+	/**
+	 * bpf_skb_[gs]et_tunnel_key(skb, key, size, flags)
+	 * retrieve or populate tunnel metadata
+	 * @skb: pointer to skb
+	 * @key: pointer to 'struct bpf_tunnel_key'
+	 * @size: size of 'struct bpf_tunnel_key'
+	 * @flags: room for future extensions
+	 * Retrun: 0 on success
+	 */
+	BPF_FUNC_skb_get_tunnel_key,
+	BPF_FUNC_skb_set_tunnel_key,
 	__BPF_FUNC_MAX_ID,
 };
 
@@ -280,4 +292,9 @@ struct __sk_buff {
 	__u32 cb[5];
 };
 
+struct bpf_tunnel_key {
+	__u32 tunnel_id;
+	__u32 remote_ipv4;
+};
+
 #endif /* _UAPI__LINUX_BPF_H__ */