collection: unexport CollectionSpec.BTF

It's currently not clear what the use case is for allowing the caller to
replace CollectionSpec.BTF, since the type graph is currently read-only.

Signed-off-by: Timo Beckers <timo@isovalent.com>

cmd/bpf2go/output.go

@@ -255,7 +255,7 @@ func output(args outputArgs) error {
 	}
 
 	// Collect any types which we've been asked for explicitly.
-	cTypes, err := collectCTypes(spec.BTF, args.cTypes)
+	cTypes, err := collectCTypes(spec.BTF(), args.cTypes)
 	if err != nil {
 		return err
 	}

collection.go

@@ -27,12 +27,12 @@ type CollectionSpec struct {
 	Maps     map[string]*MapSpec
 	Programs map[string]*ProgramSpec
 
-	// The BTF used by maps and programs.
-	BTF *btf.Spec
-
 	// ByteOrder specifies whether the ELF was compiled for
 	// big-endian or little-endian architectures.
 	ByteOrder binary.ByteOrder
+
+	// The BTF used by maps and programs.
+	btf *btf.Spec
 }
 
 // Copy returns a recursive copy of the spec.
@@ -45,7 +45,7 @@ func (cs *CollectionSpec) Copy() *CollectionSpec {
 		Maps:      make(map[string]*MapSpec, len(cs.Maps)),
 		Programs:  make(map[string]*ProgramSpec, len(cs.Programs)),
 		ByteOrder: cs.ByteOrder,
-		BTF:       cs.BTF,
+		btf:       cs.btf,
 	}
 
 	for name, spec := range cs.Maps {
@@ -59,6 +59,11 @@ func (cs *CollectionSpec) Copy() *CollectionSpec {
 	return &cpy
 }
 
+// BTF returns the BTF spec used by the CollectionSpec's Maps and Programs.
+func (cs *CollectionSpec) BTF() *btf.Spec {
+	return cs.btf
+}
+
 // RewriteMaps replaces all references to specific maps.
 //
 // Use this function to use pre-existing maps instead of creating new ones
@@ -413,8 +418,8 @@ func (cl *collectionLoader) loadMap(mapName string) (*Map, error) {
 		return nil, fmt.Errorf("missing map %s", mapName)
 	}
 
-	if mapSpec.BTF != nil && cl.coll.BTF != mapSpec.BTF.Spec {
-		return nil, fmt.Errorf("map %s: BTF doesn't match collection", mapName)
+	if mapSpec.BTF != nil && cl.coll.BTF() != mapSpec.BTF.Spec {
+		return nil, fmt.Errorf("map %s: BTF doesn't match collection %v %v", mapName, cl.coll.BTF(), mapSpec.BTF.Spec)
 	}
 
 	m, err := newMapWithOptions(mapSpec, cl.opts.Maps, cl.handles)
@@ -442,7 +447,7 @@ func (cl *collectionLoader) loadProgram(progName string) (*Program, error) {
 		return nil, fmt.Errorf("cannot load program %s: program type is unspecified", progName)
 	}
 
-	if progSpec.BTF != nil && cl.coll.BTF != progSpec.BTF.Spec() {
+	if progSpec.BTF != nil && cl.coll.BTF() != progSpec.BTF.Spec() {
 		return nil, fmt.Errorf("program %s: BTF doesn't match collection", progName)
 	}
 

collection_test.go

@@ -67,12 +67,12 @@ func TestCollectionSpecCopy(t *testing.T) {
 				License: "MIT",
 			},
 		},
-		BTF: &btf.Spec{},
+		btf: &btf.Spec{},
 	}
 	cpy := cs.Copy()
 
 	if cpy == cs {
-		t.Error("Copy returned the same pointner")
+		t.Error("Copy returned the same pointer")
 	}
 
 	if cpy.Maps["my-map"] == cs.Maps["my-map"] {
@@ -83,7 +83,7 @@ func TestCollectionSpecCopy(t *testing.T) {
 		t.Error("Copy returned same Programs")
 	}
 
-	if cpy.BTF != cs.BTF {
+	if cpy.BTF() != cs.BTF() {
 		t.Error("Copy returned different BTF")
 	}
 }

elf_reader.go

@@ -164,7 +164,7 @@ func LoadCollectionSpecFromReader(rd io.ReaderAt) (*CollectionSpec, error) {
 		return nil, fmt.Errorf("load programs: %w", err)
 	}
 
-	return &CollectionSpec{maps, progs, btfSpec, ec.ByteOrder}, nil
+	return &CollectionSpec{maps, progs, ec.ByteOrder, btfSpec}, nil
 }
 
 func loadLicense(sec *elf.Section) (string, error) {

elf_reader_test.go

@@ -143,7 +143,7 @@ func TestLoadCollectionSpec(t *testing.T) {
 			return false
 		}),
 		cmpopts.IgnoreTypes(new(btf.Map), new(btf.Program)),
-		cmpopts.IgnoreFields(CollectionSpec{}, "ByteOrder", "BTF"),
+		cmpopts.IgnoreFields(CollectionSpec{}, "ByteOrder", "btf"),
 		cmpopts.IgnoreFields(ProgramSpec{}, "Instructions", "ByteOrder"),
 		cmpopts.IgnoreUnexported(ProgramSpec{}),
 		cmpopts.IgnoreMapEntries(func(key string, _ *MapSpec) bool {