ebpf: export BPF_PSEUDO_MAP_FD to uapi

We need to export BPF_PSEUDO_MAP_FD to user space, as it's used in the
ELF BPF loader where instructions are being loaded that need map fixups.

An initial stage loads all maps into the kernel, and later on replaces
related instructions in the eBPF blob with BPF_PSEUDO_MAP_FD as source
register and the actual fd as immediate value.

The kernel verifier recognizes this keyword and replaces the map fd with
a real pointer internally.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/bpf.h

@@ -120,6 +120,8 @@ enum bpf_prog_type {
 	BPF_PROG_TYPE_SOCKET_FILTER,
 };
 
+#define BPF_PSEUDO_MAP_FD	1
+
 /* flags for BPF_MAP_UPDATE_ELEM command */
 #define BPF_ANY		0 /* create new element or update existing */
 #define BPF_NOEXIST	1 /* create new element if it didn't exist */