chore(selftest): map-of-maps-outer-low-inner-low

Introduce a new selftest that tests a map of maps with outer and inner
maps not pre-allocated in the BPF program.

selftest/map-of-maps-outer-low-inner-low/Makefile

@@ -0,0 +1 @@
+../common/Makefile

selftest/map-of-maps-outer-low-inner-low/go.mod

@@ -0,0 +1,7 @@
+module github.com/aquasecurity/libbpfgo/selftest/map-update
+
+go 1.18
+
+require github.com/aquasecurity/libbpfgo v0.4.7-libbpf-1.2.0-b2e29a1
+
+replace github.com/aquasecurity/libbpfgo => ../../

selftest/map-of-maps-outer-low-inner-low/go.sum

@@ -0,0 +1,4 @@
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/stretchr/testify v1.8.2 h1:+h33VjcLVPDHtOdpUCuF+7gSuG3yGIftsP1YvFihtJ8=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=

selftest/map-of-maps-outer-low-inner-low/main.bpf.c

@@ -0,0 +1,7 @@
+//+build ignore
+
+#include <vmlinux.h>
+
+#include <bpf/bpf_helpers.h>
+
+char LICENSE[] SEC("license") = "Dual BSD/GPL";

selftest/map-of-maps-outer-low-inner-low/main.go

@@ -0,0 +1,71 @@
+package main
+
+import "C"
+
+import (
+	"encoding/binary"
+	"log"
+	"unsafe"
+
+	bpf "github.com/aquasecurity/libbpfgo"
+)
+
+func main() {
+	bpfModule, err := bpf.NewModuleFromFile("main.bpf.o")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer bpfModule.Close()
+
+	err = bpfModule.BPFLoadObject()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	innerArray, err := bpf.CreateMap(bpf.MapTypeArray, "inner_array", 4, 4, 1, nil)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Create the "outer_hash" map, using the "inner_array" map as a prototype.
+	opts := bpf.BPFMapCreateOpts{
+		InnerMapFD: uint32(innerArray.FileDescriptor()),
+	}
+	outerHash, err := bpf.CreateMap(bpf.MapTypeHash, "outer_hash", 4, 4, 1, &opts)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Save the inner map in the "outer_hash" map, using the hash key 1917.
+	// The value used to save the element is the the inner map file descriptor,
+	// however the actual saved value is the inner map ID.
+	key1 := uint32(1917)
+	key1Unsafe := unsafe.Pointer(&key1)
+	value1 := uint32(innerArray.FileDescriptor()) // "inner_array" FD.
+	value1Unsafe := unsafe.Pointer(&value1)
+	err = outerHash.Update(key1Unsafe, value1Unsafe)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Save an element in the "inner_array" map.
+	key1 = uint32(0) // index 0
+	value1 = uint32(191711)
+	value1Unsafe = unsafe.Pointer(&value1)
+	err = innerArray.Update(key1Unsafe, value1Unsafe)
+	if err != nil {
+		log.Fatal(err)
+	}
+}
+
+func endian() binary.ByteOrder {
+	var i int32 = 0x01020304
+	u := unsafe.Pointer(&i)
+	pb := (*byte)(u)
+	b := *pb
+	if b == 0x04 {
+		return binary.LittleEndian
+	}
+
+	return binary.BigEndian
+}

selftest/map-of-maps-outer-low-inner-low/run.sh

@@ -0,0 +1 @@
+../common/run.sh