Add godoc comment

Signed-off-by: grantseltzer <grantseltzer@gmail.com>

libbpfgo.go

@@ -394,8 +394,14 @@ func bpfMapCreateOptsToC(createOpts *BPFMapCreateOpts) *C.struct_bpf_map_create_
 	return &opts
 }
 
-// CreateMap returns file descriptor of newly created map
-func (m *Module) CreateMap(mapType MapType, mapName string, keySize, valueSize, maxEntries int, opts *BPFMapCreateOpts) (*BPFMap, error) {
+// CreateMap creates a BPF map from userspace. This can be used for populating
+// BPF array of maps or hash of maps. However, this function uses a low-level
+// libbpf API; maps created in this way do not conform to libbpf map formats,
+// and therefore do not have access to libbpf high level bpf_map__* APIS
+// which causes different behavior from maps created in the kernel side code
+//
+// See usage of `bpf_map_create()` in kernel selftests for more info
+func CreateMap(mapType MapType, mapName string, keySize, valueSize, maxEntries int, opts *BPFMapCreateOpts) (*BPFMap, error) {
 	cs := C.CString(mapName)
 	fdOrError := C.bpf_map_create(uint32(mapType), cs, C.uint(keySize), C.uint(valueSize), C.uint(maxEntries), bpfMapCreateOptsToC(opts))
 	C.free(unsafe.Pointer(cs))
@@ -405,9 +411,9 @@ func (m *Module) CreateMap(mapType MapType, mapName string, keySize, valueSize,
 
 	return &BPFMap{
 		name:   mapName,
-		bpfMap: nil, //FIXME: find by name?
 		fd:     fdOrError,
-		module: m,
+		module: nil,
+		bpfMap: nil,
 	}, nil
 }
 

selftest/create-map/main.go

@@ -6,16 +6,12 @@ import (
 	"fmt"
 	"log"
 	"os"
-	"time"
+	"unsafe"
 
 	"github.com/aquasecurity/libbpfgo"
 	bpf "github.com/aquasecurity/libbpfgo"
 )
 
-func getSupposedPinPath(m *bpf.BPFMap) string {
-	return "/sys/fs/bpf/" + m.GetName()
-}
-
 func main() {
 	bpfModule, err := bpf.NewModuleFromFile("main.bpf.o")
 	if err != nil {
@@ -25,13 +21,20 @@ func main() {
 	defer bpfModule.Close()
 
 	bpfModule.BPFLoadObject()
+	opts := bpf.BPFMapCreateOpts{}
+	opts.Size = uint64(unsafe.Sizeof(opts))
 
-	m, err := bpfModule.CreateMap(libbpfgo.MapTypeArray, "foobar", 1, 1, 1, nil)
+	m, err := libbpfgo.CreateMap(libbpfgo.MapTypeHash, "foobar", 4, 4, 420, nil)
 	if err != nil {
-		log.Fatal(m, err)
+		log.Fatal(err)
 	}
 
-	fmt.Println(m)
-
-	time.Sleep(time.Second * 30)
+	key1 := uint32(1)
+	value1 := uint32(55)
+	key1Unsafe := unsafe.Pointer(&key1)
+	value1Unsafe := unsafe.Pointer(&value1)
+	err = m.Update(key1Unsafe, value1Unsafe)
+	if err != nil {
+		log.Fatal(err)
+	}
 }