pkg/fileutils: move ReadSymlinkedDirectory internal to daemon

It has no external consumers, is written with specific behavior (including
some potentially surprising behavior), making it not a good candidate to
carry in the module.

This moves it internal to the daemon as a non-exported utility, so that
it's only accessible where it's currently used.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

daemon/containerfs_linux.go

@@ -18,7 +18,6 @@ import (
 	"github.com/docker/docker/daemon/container"
 	"github.com/docker/docker/daemon/internal/mounttree"
 	"github.com/docker/docker/daemon/internal/unshare"
-	"github.com/docker/docker/pkg/fileutils"
 	containertypes "github.com/moby/moby/api/types/container"
 )
 
@@ -104,7 +103,7 @@ func (daemon *Daemon) openContainerFS(ctr *container.Container) (_ *containerFSV
 				if err != nil {
 					return err
 				}
-				if err := fileutils.CreateIfNotExists(dest, stat.IsDir()); err != nil {
+				if err := createIfNotExists(dest, stat.IsDir()); err != nil {
 					return err
 				}
 
@@ -252,6 +251,27 @@ func (vw *containerFSView) Stat(ctx context.Context, path string) (*containertyp
 	return stat, err
 }
 
+// createIfNotExists creates a file or a directory only if it does not already exist.
+func createIfNotExists(dest string, isDir bool) error {
+	if _, err := os.Stat(dest); err != nil {
+		// FIXME(thaJeztah): this ignores any other error (which may include "dest" is of the wrong type, or permission errors).
+		if os.IsNotExist(err) {
+			if isDir {
+				return os.MkdirAll(dest, 0o755)
+			}
+			if err := os.MkdirAll(filepath.Dir(dest), 0o755); err != nil {
+				return err
+			}
+			f, err := os.OpenFile(dest, os.O_CREATE, 0o755)
+			if err != nil {
+				return err
+			}
+			_ = f.Close()
+		}
+	}
+	return nil
+}
+
 // makeMountRRO makes the mount recursively read-only.
 func makeMountRRO(dest string) error {
 	attr := &unix.MountAttr{

daemon/containerfs_linux_test.go

@@ -0,0 +1,39 @@
+package daemon
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"gotest.tools/v3/assert"
+)
+
+func TestCreateIfNotExists(t *testing.T) {
+	t.Run("directory", func(t *testing.T) {
+		toCreate := filepath.Join(t.TempDir(), "tocreate")
+
+		err := createIfNotExists(toCreate, true)
+		assert.NilError(t, err)
+
+		fileinfo, err := os.Stat(toCreate)
+		assert.NilError(t, err, "Did not create destination")
+		assert.Assert(t, fileinfo.IsDir(), "Should have been a dir, seems it's not")
+
+		err = createIfNotExists(toCreate, true)
+		assert.NilError(t, err, "Should not fail if already exists")
+	})
+	t.Run("file", func(t *testing.T) {
+		toCreate := filepath.Join(t.TempDir(), "file/to/create")
+
+		err := createIfNotExists(toCreate, false)
+		assert.NilError(t, err)
+
+		fileinfo, err := os.Stat(toCreate)
+		assert.NilError(t, err, "Did not create destination")
+
+		assert.Assert(t, !fileinfo.IsDir(), "Should have been a file, but created a directory")
+
+		err = createIfNotExists(toCreate, true)
+		assert.NilError(t, err, "Should not fail if already exists")
+	})
+}

pkg/fileutils/fileutils.go

@@ -27,23 +27,3 @@ func ReadSymlinkedDirectory(path string) (realPath string, _ error) {
 	}
 	return realPath, nil
 }
-
-// CreateIfNotExists creates a file or a directory only if it does not already exist.
-func CreateIfNotExists(path string, isDir bool) error {
-	if _, err := os.Stat(path); err != nil {
-		if os.IsNotExist(err) {
-			if isDir {
-				return os.MkdirAll(path, 0o755)
-			}
-			if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
-				return err
-			}
-			f, err := os.OpenFile(path, os.O_CREATE, 0o755)
-			if err != nil {
-				return err
-			}
-			_ = f.Close()
-		}
-	}
-	return nil
-}

pkg/fileutils/fileutils_test.go

@@ -107,35 +107,3 @@ func TestReadSymlinkedDirectoryToFile(t *testing.T) {
 		t.Errorf("failed to remove symlink: %s", err)
 	}
 }
-
-func TestCreateIfNotExistsDir(t *testing.T) {
-	folderToCreate := filepath.Join(t.TempDir(), "tocreate")
-
-	if err := CreateIfNotExists(folderToCreate, true); err != nil {
-		t.Fatal(err)
-	}
-	fileinfo, err := os.Stat(folderToCreate)
-	if err != nil {
-		t.Fatalf("Should have create a folder, got %v", err)
-	}
-
-	if !fileinfo.IsDir() {
-		t.Errorf("Should have been a dir, seems it's not")
-	}
-}
-
-func TestCreateIfNotExistsFile(t *testing.T) {
-	fileToCreate := filepath.Join(t.TempDir(), "file/to/create")
-
-	if err := CreateIfNotExists(fileToCreate, false); err != nil {
-		t.Error(err)
-	}
-	fileinfo, err := os.Stat(fileToCreate)
-	if err != nil {
-		t.Fatalf("Should have create a file, got %v", err)
-	}
-
-	if fileinfo.IsDir() {
-		t.Errorf("Should have been a file, seems it's not")
-	}
-}