Support ARRAY_OF_MAPS and HASH_OF_MAPS

[masibw]

Hi all, thanks for the good library.

I wanna use ARRAY_OF_MAPS and HASH_OF_MAPS. I think I have to provide a file descriptor of the maps. But I think there is no way to get the table file descriptor.

Maybe ID is not file descriptor. We need int(C.bpf_table_fd_id(mod, table.id)), , is It?

Also, if the key of the parent table's key is a string and the value is a file descriptor, I don't think it is possible to set this value even if the Get File Descriptor function exists.

test.c

BPF_ARRAY(innerMap, int, 32);
BPF_HASH_OF_MAPS(parentMap, "innerMap", 10);

... some codes ...

main.go

type ParentKey struct{
  ID string
}

	m := bpf.NewModule(string(bpfText), []string{})

	parentTable := bpf.NewTable(m.TableId("parentMap"), m)

	innerTable := bpf.NewTable(m.TableId("innerMap"), m)
        key, _ := innerTable.KeyStrToBytes("1")
        leaf, _ := innerTable.LeafStrToBytes("11")

	if err := table.Set(key, leaf); err != nil {
		fmt.Fprintf(os.Stderr, "Failed to add data to rules: %s\n", err)
		os.Exit(1)
	}

	parentKey := &ParentKey{
	     ID: "test_id",
	}

        fd := innerTable.Fd() // I need this function

        // I think `cgo argument has Go pointer to Go pointer` error will be occured, also  parentTable.Set is not satisfied this usecase. 
	if err := parentTable.SetP(parentKey, fd); err != nil {
		fmt.Fprintf(os.Stderr, "Failed to add data to policyList: %s\n", err)
		os.Exit(1)
	}

The assumption is that if I want to use a string in a Map, I need to wrap it in a structure, right?

Maybe We need SetMap(key unsafe.Pointer, fd int) error