add function to return all inherited files

fds.go

@@ -323,6 +323,36 @@ func (f *Fds) addSyscallConnLocked(kind, network, addr string, conn syscall.Conn
 	return nil
 }
 
+// Files returns all inherited files and mark them as used.
+//
+// The descriptors may be in blocking mode.
+func (f *Fds) Files() ([]*os.File, error) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+
+	var files []*os.File
+
+	for key, file := range f.inherited {
+		if key[0] != fdKind {
+			continue
+		}
+
+		// Make a copy of the file, since we don't want to
+		// allow the caller to invalidate fds in f.inherited.
+		dup, err := dupFd(file.fd, key)
+		if err != nil {
+			return nil, err
+		}
+
+		f.used[key] = file
+		delete(f.inherited, key)
+
+		files = append(files, dup.File)
+	}
+
+	return files, nil
+}
+
 // File returns an inherited file or nil.
 //
 // The descriptor may be in blocking mode.

fds_test.go

@@ -315,3 +315,62 @@ func TestFdsFile(t *testing.T) {
 	}
 	file.Close()
 }
+
+func TestFdsFiles(t *testing.T) {
+	r1, w1, err := os.Pipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer r1.Close()
+
+	r2, w2, err := os.Pipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer r2.Close()
+
+	testcases := []struct {
+		f        *os.File
+		name     string
+		expected string
+	}{
+		{
+			w1,
+			"test1",
+			"fd:test1:",
+		},
+		{
+			w2,
+			"test2",
+			"fd:test2:",
+		},
+	}
+
+	parent := newFds(nil, nil)
+	for _, tc := range testcases {
+		if err := parent.AddFile(tc.name, tc.f); err != nil {
+			t.Fatal("Can't add file:", err)
+		}
+		tc.f.Close()
+	}
+
+	child := newFds(parent.copy(), nil)
+	files, err := child.Files()
+	if err != nil {
+		t.Fatal("Can't get inherited files:", err)
+	}
+
+	if len(files) != len(testcases) {
+		t.Fatalf("Expected %d files, got %d", len(testcases), len(files))
+	}
+
+	for i, ff := range files {
+		tc := testcases[i]
+
+		if ff.Name() != tc.expected {
+			t.Errorf("Expected file %q, got %q", tc.expected, ff.Name())
+		}
+
+		ff.Close()
+	}
+}