Extend the metadata backend to read the attributes from a locked source

pkg/storage/utils/decomposedfs/lookup/lookup.go

@@ -295,15 +295,15 @@ func (lu *Lookup) CopyMetadata(src, target string, filter func(attributeName str
 // The optional filter function can be used to filter by attribute name, e.g. by checking a prefix
 // For the source file, a matching lockedfile is required.
 // NOTE: target resource will be write locked!
-func (lu *Lookup) CopyMetadataWithSourceLock(source, target string, filter func(attributeName string) bool, readLock *lockedfile.File) (err error) {
+func (lu *Lookup) CopyMetadataWithSourceLock(sourcePath, targetPath string, filter func(attributeName string) bool, lockedSource *lockedfile.File) (err error) {
 	switch {
-	case readLock == nil:
+	case lockedSource == nil:
 		return errors.New("no lock provided")
-	case readLock.File.Name() != lu.MetadataBackend().MetadataPath(source):
+	case lockedSource.File.Name() != lu.MetadataBackend().MetadataPath(sourcePath):
 		return errors.New("lockpath does not match filepath")
 	}
 
-	attrs, err := lu.metadataBackend.All(source)
+	attrs, err := lu.metadataBackend.AllWithLockedSource(sourcePath, lockedSource)
 	if err != nil {
 		return err
 	}
@@ -315,5 +315,5 @@ func (lu *Lookup) CopyMetadataWithSourceLock(source, target string, filter func(
 		}
 	}
 
-	return lu.MetadataBackend().SetMultiple(target, newAttrs, true)
+	return lu.MetadataBackend().SetMultiple(targetPath, newAttrs, true)
 }

pkg/storage/utils/decomposedfs/metadata/messagepack_backend.go

@@ -57,14 +57,14 @@ func NewMessagePackBackend(rootPath string, o options.CacheOptions) MessagePackB
 func (b MessagePackBackend) All(path string) (map[string][]byte, error) {
 	path = b.MetadataPath(path)
 
-	return b.loadAttributes(path)
+	return b.loadAttributes(path, nil)
 }
 
 // Get an extended attribute value for the given key
 func (b MessagePackBackend) Get(path, key string) ([]byte, error) {
 	path = b.MetadataPath(path)
 
-	attribs, err := b.loadAttributes(path)
+	attribs, err := b.loadAttributes(path, nil)
 	if err != nil {
 		return []byte{}, err
 	}
@@ -79,7 +79,7 @@ func (b MessagePackBackend) Get(path, key string) ([]byte, error) {
 func (b MessagePackBackend) GetInt64(path, key string) (int64, error) {
 	path = b.MetadataPath(path)
 
-	attribs, err := b.loadAttributes(path)
+	attribs, err := b.loadAttributes(path, nil)
 	if err != nil {
 		return 0, err
 	}
@@ -99,7 +99,7 @@ func (b MessagePackBackend) GetInt64(path, key string) (int64, error) {
 func (b MessagePackBackend) List(path string) ([]string, error) {
 	path = b.MetadataPath(path)
 
-	attribs, err := b.loadAttributes(path)
+	attribs, err := b.loadAttributes(path, nil)
 	if err != nil {
 		return nil, err
 	}
@@ -125,6 +125,13 @@ func (b MessagePackBackend) Remove(path, key string) error {
 	return b.saveAttributes(path, nil, []string{key}, true)
 }
 
+// AllWithLockedSource reads all extended attributes from the given reader (if possible).
+// The path argument is used for storing the data in the cache
+func (b MessagePackBackend) AllWithLockedSource(path string, source io.Reader) (map[string][]byte, error) {
+	path = b.MetadataPath(path)
+	return b.loadAttributes(path, source)
+}
+
 func (b MessagePackBackend) saveAttributes(path string, setAttribs map[string][]byte, deleteAttribs []string, acquireLock bool) error {
 	var (
 		f   readWriteCloseSeekTruncater
@@ -188,31 +195,32 @@ func (b MessagePackBackend) saveAttributes(path string, setAttribs map[string][]
 	return b.metaCache.PushToCache(b.cacheKey(path), attribs)
 }
 
-func (b MessagePackBackend) loadAttributes(path string) (map[string][]byte, error) {
+func (b MessagePackBackend) loadAttributes(path string, source io.Reader) (map[string][]byte, error) {
 	attribs := map[string][]byte{}
 	err := b.metaCache.PullFromCache(b.cacheKey(path), &attribs)
 	if err == nil {
 		return attribs, err
 	}
 
-	lockedFile, err := lockedfile.Open(path)
-
-	// // No cached entry found. Read from storage and store in cache
-	if err != nil {
-		if os.IsNotExist(err) {
-			// some of the caller rely on ENOTEXISTS to be returned when the
-			// actual file (not the metafile) does not exist in order to
-			// determine whether a node exists or not -> stat the actual node
-			_, err := os.Stat(strings.TrimSuffix(path, ".mpk"))
-			if err != nil {
-				return nil, err
+	if source == nil {
+		source, err = lockedfile.Open(path)
+		// // No cached entry found. Read from storage and store in cache
+		if err != nil {
+			if os.IsNotExist(err) {
+				// some of the caller rely on ENOTEXISTS to be returned when the
+				// actual file (not the metafile) does not exist in order to
+				// determine whether a node exists or not -> stat the actual node
+				_, err := os.Stat(strings.TrimSuffix(path, ".mpk"))
+				if err != nil {
+					return nil, err
+				}
+				return attribs, nil // no attributes set yet
 			}
-			return attribs, nil // no attributes set yet
 		}
+		defer source.(*lockedfile.File).Close()
 	}
-	defer lockedFile.Close()
 
-	msgBytes, err := io.ReadAll(lockedFile)
+	msgBytes, err := io.ReadAll(source)
 	if err != nil {
 		return nil, err
 	}

pkg/storage/utils/decomposedfs/metadata/metadata.go

@@ -18,7 +18,10 @@
 
 package metadata
 
-import "errors"
+import (
+	"errors"
+	"io"
+)
 
 var errUnconfiguredError = errors.New("no metadata backend configured. Bailing out")
 
@@ -36,6 +39,8 @@ type Backend interface {
 	Rename(oldPath, newPath string) error
 	IsMetaFile(path string) bool
 	MetadataPath(path string) string
+
+	AllWithLockedSource(path string, source io.Reader) (map[string][]byte, error)
 }
 
 // NullBackend is the default stub backend, used to enforce the configuration of a proper backend
@@ -76,3 +81,9 @@ func (NullBackend) Rename(oldPath, newPath string) error { return errUnconfigure
 
 // MetadataPath returns the path of the file holding the metadata for the given path
 func (NullBackend) MetadataPath(path string) string { return "" }
+
+// AllWithLockedSource reads all extended attributes from the given reader
+// The path argument is used for storing the data in the cache
+func (NullBackend) AllWithLockedSource(path string, source io.Reader) (map[string][]byte, error) {
+	return nil, errUnconfiguredError
+}

pkg/storage/utils/decomposedfs/metadata/xattrs_backend.go

@@ -19,6 +19,7 @@
 package metadata
 
 import (
+	"io"
 	"os"
 	"path/filepath"
 	"strconv"
@@ -166,3 +167,9 @@ func cleanupLockfile(f *lockedfile.File) {
 	_ = f.Close()
 	_ = os.Remove(f.Name())
 }
+
+// AllFromSource reads all extended attributes from the given reader.
+// The path argument is used for storing the data in the cache
+func (b XattrsBackend) AllWithLockedSource(path string, _ io.Reader) (map[string][]byte, error) {
+	return b.All(path)
+}