Add atomicdir package

pkg/operator/staticpod/internal/atomicdir contains internal helpers for
performing atomic operations on directories.

This patch contains only a standalone swap function, which will be
subsequenty used for synchronizing directory with the given state.

Author: tchap

pkg/operator/staticpod/installerpod/cmd.go

@@ -3,14 +3,15 @@ package installerpod
 import (
 	"context"
 	"fmt"
-	"k8s.io/utils/clock"
 	"os"
 	"path"
 	"sort"
 	"strconv"
 	"strings"
 	"time"
 
+	"k8s.io/utils/clock"
+
 	"k8s.io/apimachinery/pkg/util/wait"
 
 	"github.com/blang/semver/v4"

pkg/operator/staticpod/internal/atomicdir/swap_linux.go

@@ -0,0 +1,22 @@
+//go:build linux
+
+package atomicdir
+
+import (
+	"golang.org/x/sys/unix"
+)
+
+// swap can be used to exchange two directories atomically.
+func swap(firstDir, secondDir string) error {
+	// Renameat2 can be used to exchange two directories atomically when RENAME_EXCHANGE flag is specified.
+	// The paths to be exchanged can be specified in multiple ways:
+	//
+	//   * You can specify a file descriptor and a relative path to that descriptor.
+	//   * You can specify an absolute path, in which case the file descriptor is ignored.
+	//
+	// We use AT_FDCWD special file descriptor so that when any of the paths is relative,
+	// it's relative to the current working directory.
+	//
+	// For more details, see `man renameat2` as that is the associated C library function.
+	return unix.Renameat2(unix.AT_FDCWD, firstDir, unix.AT_FDCWD, secondDir, unix.RENAME_EXCHANGE)
+}

pkg/operator/staticpod/internal/atomicdir/swap_linux_test.go

@@ -0,0 +1,251 @@
+//go:build linux
+
+package atomicdir
+
+import (
+	"bytes"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+
+	"k8s.io/apimachinery/pkg/util/sets"
+)
+
+func TestSwap(t *testing.T) {
+	stateFirst := directoryState{
+		"1.txt": {
+			Content: []byte("hello 1 world"),
+			Perm:    0600,
+		},
+		"2.txt": {
+			Content: []byte("hello 2 world"),
+			Perm:    0400,
+		},
+	}
+	stateSecond := directoryState{
+		"a.txt": {
+			Content: []byte("hello a world"),
+			Perm:    0600,
+		},
+	}
+	stateEmpty := directoryState{}
+
+	expectNoError := func(t *testing.T, err error) {
+		t.Helper()
+		if err != nil {
+			t.Fatalf("Expected no error, got %v", err)
+		}
+	}
+
+	checkSuccess := func(t *testing.T, pathFirst string, stateFirst directoryState, pathSecond string, stateSecond directoryState, err error) {
+		t.Helper()
+		expectNoError(t, err)
+
+		// Make sure the contents are swapped.
+		stateFirst.CheckDirectoryMatches(t, pathSecond)
+		stateSecond.CheckDirectoryMatches(t, pathFirst)
+	}
+
+	testCases := []struct {
+		name        string
+		setup       func(t *testing.T, tmpDir string) (pathFirst string, stateFirst directoryState, pathSecond string, stateSecond directoryState)
+		checkResult func(t *testing.T, pathFirst string, stateFirst directoryState, pathSecond string, stateSecond directoryState, err error)
+	}{
+		{
+			name: "success with absolute paths",
+			setup: func(t *testing.T, tmpDir string) (string, directoryState, string, directoryState) {
+				pathFirst := filepath.Join(tmpDir, "first")
+				pathSecond := filepath.Join(tmpDir, "second")
+
+				stateFirst.Write(t, pathFirst)
+				stateSecond.Write(t, pathSecond)
+
+				return pathFirst, stateFirst, pathSecond, stateSecond
+			},
+			checkResult: checkSuccess,
+		},
+		{
+			name: "success with the first path relative",
+			setup: func(t *testing.T, tmpDir string) (string, directoryState, string, directoryState) {
+				pathFirst := filepath.Join(tmpDir, "first")
+				pathSecond := filepath.Join(tmpDir, "second")
+
+				stateFirst.Write(t, pathFirst)
+				stateSecond.Write(t, pathSecond)
+
+				cwd, err := os.Getwd()
+				expectNoError(t, err)
+
+				relFirst, err := filepath.Rel(cwd, pathFirst)
+				expectNoError(t, err)
+
+				return relFirst, stateFirst, pathSecond, stateSecond
+			},
+			checkResult: checkSuccess,
+		},
+		{
+			name: "success with the second path relative",
+			setup: func(t *testing.T, tmpDir string) (string, directoryState, string, directoryState) {
+				pathFirst := filepath.Join(tmpDir, "first")
+				pathSecond := filepath.Join(tmpDir, "second")
+
+				stateFirst.Write(t, pathFirst)
+				stateSecond.Write(t, pathSecond)
+
+				cwd, err := os.Getwd()
+				expectNoError(t, err)
+
+				relSecond, err := filepath.Rel(cwd, pathSecond)
+				expectNoError(t, err)
+
+				return pathFirst, stateFirst, relSecond, stateSecond
+			},
+			checkResult: checkSuccess,
+		},
+		{
+			name: "success with an empty directory",
+			setup: func(t *testing.T, tmpDir string) (string, directoryState, string, directoryState) {
+				pathFirst := filepath.Join(tmpDir, "first")
+				pathSecond := filepath.Join(tmpDir, "second")
+
+				stateFirst.Write(t, pathFirst)
+				stateEmpty.Write(t, pathSecond)
+
+				return pathFirst, stateFirst, pathSecond, stateEmpty
+			},
+			checkResult: checkSuccess,
+		},
+		{
+			name: "success with both directories empty",
+			setup: func(t *testing.T, tmpDir string) (string, directoryState, string, directoryState) {
+				pathFirst := filepath.Join(tmpDir, "first")
+				pathSecond := filepath.Join(tmpDir, "second")
+
+				stateEmpty.Write(t, pathFirst)
+				stateEmpty.Write(t, pathSecond)
+
+				return pathFirst, stateEmpty, pathSecond, stateEmpty
+			},
+			checkResult: checkSuccess,
+		},
+		{
+			name: "error with the first directory not existing",
+			setup: func(t *testing.T, tmpDir string) (string, directoryState, string, directoryState) {
+				pathFirst := filepath.Join(tmpDir, "first")
+				pathSecond := filepath.Join(tmpDir, "second")
+
+				expectNoError(t, os.Mkdir(pathSecond, 0755))
+
+				return pathFirst, stateEmpty, pathSecond, stateEmpty
+			},
+			checkResult: func(t *testing.T, pathFirst string, stateFirst directoryState, pathSecond string, stateSecond directoryState, err error) {
+				if !os.IsNotExist(err) {
+					t.Errorf("Expected a directory not exists error, got %v", err)
+				}
+			},
+		},
+		{
+			name: "error with the second directory not existing",
+			setup: func(t *testing.T, tmpDir string) (string, directoryState, string, directoryState) {
+				pathFirst := filepath.Join(tmpDir, "first")
+				pathSecond := filepath.Join(tmpDir, "second")
+
+				expectNoError(t, os.Mkdir(pathFirst, 0755))
+
+				return pathFirst, stateEmpty, pathSecond, stateEmpty
+			},
+			checkResult: func(t *testing.T, pathFirst string, stateFirst directoryState, pathSecond string, stateSecond directoryState, err error) {
+				if !os.IsNotExist(err) {
+					t.Errorf("Expected a directory not exists error, got %v", err)
+				}
+			},
+		},
+		{
+			name: "error with no directory existing",
+			setup: func(t *testing.T, tmpDir string) (string, directoryState, string, directoryState) {
+				pathFirst := filepath.Join(tmpDir, "first")
+				pathSecond := filepath.Join(tmpDir, "second")
+
+				return pathFirst, stateEmpty, pathSecond, stateEmpty
+			},
+			checkResult: func(t *testing.T, pathFirst string, stateFirst directoryState, pathSecond string, stateSecond directoryState, err error) {
+				if !os.IsNotExist(err) {
+					t.Errorf("Expected a directory not exists error, got %v", err)
+				}
+			},
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			pathFirst, stateFirst, pathSecond, stateSecond := tc.setup(t, t.TempDir())
+			tc.checkResult(t, pathFirst, stateFirst, pathSecond, stateSecond, swap(pathFirst, pathSecond))
+		})
+	}
+}
+
+type fileState struct {
+	Content []byte
+	Perm    os.FileMode
+}
+
+type directoryState map[string]fileState
+
+func (dir directoryState) Write(t *testing.T, path string) {
+	if err := os.MkdirAll(path, 0755); err != nil && !os.IsExist(err) {
+		t.Fatalf("Failed to create directory %q: %v", path, err)
+	}
+
+	for filename, state := range dir {
+		fullFilename := filepath.Join(path, filename)
+		if err := os.WriteFile(fullFilename, state.Content, state.Perm); err != nil {
+			t.Fatalf("Failed to write file %q: %v", fullFilename, err)
+		}
+	}
+}
+
+func (dir directoryState) CheckDirectoryMatches(t *testing.T, path string) {
+	entries, err := os.ReadDir(path)
+	if err != nil {
+		t.Fatalf("Failed to read directory %q: %v", path, err)
+	}
+
+	expectedFiles := sets.KeySet(dir)
+	for _, entry := range entries {
+		// Mark the file as visited.
+		expectedFiles.Delete(entry.Name())
+
+		// Get the expected state.
+		state, ok := dir[entry.Name()]
+		if !ok {
+			t.Errorf("Directory %q contains unexpected file %q", path, entry.Name())
+			continue
+		}
+
+		// Check permissions.
+		info, err := entry.Info()
+		if err != nil {
+			t.Errorf("Failed to stat file %q: %v", entry.Name(), err)
+			continue
+		}
+
+		if info.Mode() != state.Perm {
+			t.Errorf("Unexpected permissions on file %q: expected %v, got %v", entry.Name(), state.Perm, info.Mode())
+		}
+
+		// Check file content.
+		content, err := os.ReadFile(filepath.Join(path, entry.Name()))
+		if err != nil {
+			t.Errorf("Failed to read file %q: %v", entry.Name(), err)
+			continue
+		}
+		if !bytes.Equal(state.Content, content) {
+			t.Errorf("Unexpected content in file %q:\n%v", entry.Name(), cmp.Diff(string(state.Content), string(content)))
+		}
+	}
+	if expectedFiles.Len() != 0 {
+		t.Errorf("Some expected files were not found in directory %q: %s", path, expectedFiles.UnsortedList())
+	}
+}

pkg/operator/staticpod/internal/atomicdir/swap_other.go

@@ -0,0 +1,10 @@
+//go:build !linux
+
+package atomicdir
+
+// swap can be used to exchange two directories atomically.
+//
+// This function is only implemented for Linux and returns an error on other platforms.
+func swap(firstDir, secondDir string) error {
+	return errors.New("swap is not supported on this platform")
+}