feat(map): introduce GetMapFDByID()

This function allows to get a file descriptor of a map by its ID.

map-common.go

@@ -125,6 +125,16 @@ type BPFMapInfo struct {
 	MapExtra              uint64
 }
 
+// GetMapFDByID returns a file descriptor for the map with the given ID.
+func GetMapFDByID(id uint32) (int, error) {
+	fdC := C.bpf_map_get_fd_by_id(C.uint(id))
+	if fdC < 0 {
+		return int(fdC), fmt.Errorf("could not find map id %d: %w", id, syscall.Errno(-fdC))
+	}
+
+	return int(fdC), nil
+}
+
 // GetMapInfoByFD returns the BPFMapInfo for the map with the given file descriptor.
 func GetMapInfoByFD(fd int) (*BPFMapInfo, error) {
 	var info C.struct_bpf_map_info

selftest/map-getfdbyid/Makefile

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

selftest/map-getfdbyid/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-getfdbyid/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-getfdbyid/main.bpf.c

@@ -0,0 +1,14 @@
+//+build ignore
+
+#include <vmlinux.h>
+
+#include <bpf/bpf_helpers.h>
+
+struct {
+    __uint(type, BPF_MAP_TYPE_HASH);
+    __type(key, u32);
+    __type(value, u32);
+    __uint(max_entries, 1);
+} tester SEC(".maps");
+
+char LICENSE[] SEC("license") = "Dual BSD/GPL";

selftest/map-getfdbyid/main.go

@@ -0,0 +1,85 @@
+package main
+
+import "C"
+
+import (
+	"log"
+
+	bpf "github.com/aquasecurity/libbpfgo"
+)
+
+func main() {
+	bpfModule, err := bpf.NewModuleFromFile("main.bpf.o")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer bpfModule.Close()
+
+	bpfModule.BPFLoadObject()
+
+	testerMap, err := bpfModule.GetMap("tester")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Get info about the "tester" map
+	infoTester, err := bpf.GetMapInfoByFD(testerMap.FileDescriptor())
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Get a new FD pointing to the "tester" map
+	newFD, err := bpf.GetMapFDByID(infoTester.ID)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Get info about the "tester" map again, this time using the new FD
+	infoNewFD, err := bpf.GetMapInfoByFD(newFD)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	if infoTester.Type != infoNewFD.Type {
+		log.Fatal("Types do not match")
+	}
+	if infoTester.ID != infoNewFD.ID {
+		log.Fatal("IDs do not match")
+	}
+	if infoTester.KeySize != infoNewFD.KeySize {
+		log.Fatal("Key sizes do not match")
+	}
+	if infoTester.ValueSize != infoNewFD.ValueSize {
+		log.Fatal("Value sizes do not match")
+	}
+	if infoTester.MaxEntries != infoNewFD.MaxEntries {
+		log.Fatal("Max entries do not match")
+	}
+	if infoTester.MapFlags != infoNewFD.MapFlags {
+		log.Fatal("Map flags do not match")
+	}
+	if infoTester.Name != infoNewFD.Name {
+		log.Fatal("Names do not match")
+	}
+	if infoTester.IfIndex != infoNewFD.IfIndex {
+		log.Fatal("Ifindexes do not match")
+	}
+	if infoTester.NetnsDev != infoNewFD.NetnsDev {
+		log.Fatal("Netns do not match")
+	}
+	if infoTester.NetnsIno != infoNewFD.NetnsIno {
+		log.Fatal("Netns inodes do not match")
+	}
+	if infoTester.BTFID != infoNewFD.BTFID {
+		log.Fatal("BTF IDs do not match")
+	}
+	if infoTester.BTFKeyTypeID != infoNewFD.BTFKeyTypeID {
+		log.Fatal("BTF key type IDs do not match")
+	}
+	if infoTester.BTFValueTypeID != infoNewFD.BTFValueTypeID {
+		log.Fatal("BTF value type IDs do not match")
+	}
+	if infoTester.MapExtra != infoNewFD.MapExtra {
+		log.Fatal("Map extras do not match")
+	}
+}

selftest/map-getfdbyid/run.sh

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