lookup: Support tbid option

Support bpf_fib_lookup with tbid option. We expose table option similar
to the iproute2. It requires an additional flag BFP_FIB_LOOKUP_TBID to
distinguish table 0 and unspecified, but we don't expose the flag
explicitly. Since we can distinguish them with the table option
specified vs unspecifid. When the table option is specified, we set it
transparently with BPF_FIB_LOOKUP_DIRECT.

Signed-off-by: Yutaro Hayakawa <[email protected]>

cmd/lookup.go

@@ -44,6 +44,7 @@ type lookupIn struct {
 	IPv6FlowInfo *uint32
 	SrcAddr      netip.Addr
 	DstAddr      netip.Addr
+	TableID      *uint32
 }
 
 func (in *lookupIn) marshal() []byte {
@@ -93,8 +94,14 @@ func (in *lookupIn) marshal() []byte {
 		a := in.DstAddr.As16()
 		buf.Write(a[:])
 	}
+	// param->tbid
+	if in.TableID != nil {
+		binary.Write(buf, binary.NativeEndian, in.TableID)
+	} else {
+		binary.Write(buf, binary.NativeEndian, uint32(0))
+	}
 	// Padding
-	buf.Write(bytes.Repeat([]byte{0}, 16))
+	buf.Write(bytes.Repeat([]byte{0}, 12))
 	return buf.Bytes()
 }
 
@@ -264,6 +271,13 @@ var lookupCmd = &cobra.Command{
 		if output, _ := cmd.Flags().GetBool("output"); output {
 			flags |= BFP_FIB_LOOKUP_OUTPUT
 		}
+		if in.TableID != nil {
+			if flags&BFP_FIB_LOOKUP_DIRECT == 0 {
+				cmd.PrintErrf("Forcefully setting BFP_FIB_LOOKUP_DIRECT option since you specified table option which requires direct lookup. To suppress this message, set --direct flag explicitly.\n")
+				flags |= BFP_FIB_LOOKUP_DIRECT
+			}
+			flags |= BFP_FIB_LOOKUP_TBID
+		}
 
 		// Serialize input parameters to write struct bpf_fib_lookup to map
 		param := in.marshal()
@@ -491,6 +505,22 @@ var lookupCmdOpts = map[string]lookupOpt{
 		},
 		probe: func() bool { return true },
 	},
+	"table": {
+		desc: []string{"table", "<table id>", "Table ID"},
+		handle: func(in *lookupIn, args []string) (int, error) {
+			if len(args) == 0 {
+				return 0, fmt.Errorf("table is unspecified")
+			}
+			tableID, err := strconv.ParseUint(args[0], 10, 32)
+			if err != nil {
+				return 0, fmt.Errorf("cannot parse table id: %w", err)
+			}
+			tableID32 := uint32(tableID)
+			in.TableID = &tableID32
+			return 1, nil
+		},
+		probe: func() bool { return true },
+	},
 }
 
 func parseLookupArgs(in *lookupIn, args []string) error {