Reorganize chunkedDiffer

Try to split fields by purpose, and document some of the context.

For consistency, use the same order in the struct literals.

Only reorders existing fields, should not change behavior.

Signed-off-by: Miloslav Trmač <[email protected]>

pkg/chunked/storage_linux.go

@@ -62,46 +62,53 @@ const (
 type compressedFileType int
 
 type chunkedDiffer struct {
+	// Initial parameters, used throughout and never modified
+	// ==========
+	pullOptions pullOptions
 	stream      ImageSourceSeekable
-	manifest    []byte
-	toc         *minimal.TOC // The parsed contents of manifest, or nil if not yet available
-	tarSplit    []byte
-	layersCache *layersCache
-	tocOffset   int64
-	fileType    compressedFileType
-
-	copyBuffer []byte
-
-	gzipReader *pgzip.Reader
-	zstdReader *zstd.Decoder
-	rawReader  io.Reader
-
-	// tocDigest is the digest of the TOC document when the layer
-	// is partially pulled.
-	tocDigest digest.Digest
+	// blobDigest is the digest of the whole compressed layer.  It is used if
+	// convertToZstdChunked to validate a layer when it is converted since there
+	// is no TOC referenced by the manifest.
+	blobDigest digest.Digest
+	blobSize   int64
 
+	// Input format
+	// ==========
+	fileType compressedFileType
 	// convertedToZstdChunked is set to true if the layer needs to
 	// be converted to the zstd:chunked format before it can be
 	// handled.
 	convertToZstdChunked bool
 
+	// Chunked metadata
+	// This is usually set in GetDiffer, but if convertToZstdChunked, it is only computed in chunkedDiffer.ApplyDiff
+	// ==========
+	// tocDigest is the digest of the TOC document when the layer
+	// is partially pulled, or "" if not relevant to consumers.
+	tocDigest           digest.Digest
+	tocOffset           int64
+	manifest            []byte
+	toc                 *minimal.TOC // The parsed contents of manifest, or nil if not yet available
+	tarSplit            []byte
+	uncompressedTarSize int64 // -1 if unknown
 	// skipValidation is set to true if the individual files in
 	// the layer are trusted and should not be validated.
 	skipValidation bool
 
-	// blobDigest is the digest of the whole compressed layer.  It is used if
-	// convertToZstdChunked to validate a layer when it is converted since there
-	// is no TOC referenced by the manifest.
-	blobDigest digest.Digest
-
-	blobSize            int64
-	uncompressedTarSize int64 // -1 if unknown
-
-	pullOptions pullOptions
-
-	useFsVerity     graphdriver.DifferFsVerity
+	// Long-term caches
+	// This is set in GetDiffer, when the caller must not hold any storage locks, and later consumed in .ApplyDiff()
+	// ==========
+	layersCache     *layersCache
+	copyBuffer      []byte
+	fsVerityMutex   sync.Mutex // protects fsVerityDigests
 	fsVerityDigests map[string]string
-	fsVerityMutex   sync.Mutex
+
+	// Private state of .ApplyDiff
+	// ==========
+	gzipReader  *pgzip.Reader
+	zstdReader  *zstd.Decoder
+	rawReader   io.Reader
+	useFsVerity graphdriver.DifferFsVerity
 }
 
 var xattrsToIgnore = map[string]interface{}{
@@ -277,15 +284,18 @@ func makeConvertFromRawDiffer(store storage.Store, blobDigest digest.Digest, blo
 	}
 
 	return &chunkedDiffer{
-		fsVerityDigests:      make(map[string]string),
-		blobDigest:           blobDigest,
-		blobSize:             blobSize,
-		uncompressedTarSize:  -1, // Will be computed later
+		pullOptions: pullOptions,
+		stream:      iss,
+		blobDigest:  blobDigest,
+		blobSize:    blobSize,
+
 		convertToZstdChunked: true,
-		copyBuffer:           makeCopyBuffer(),
-		layersCache:          layersCache,
-		pullOptions:          pullOptions,
-		stream:               iss,
+
+		uncompressedTarSize: -1, // Will be computed later
+
+		layersCache:     layersCache,
+		copyBuffer:      makeCopyBuffer(),
+		fsVerityDigests: make(map[string]string),
 	}, nil
 }
 
@@ -317,19 +327,22 @@ func makeZstdChunkedDiffer(store storage.Store, blobSize int64, tocDigest digest
 	}
 
 	return &chunkedDiffer{
-		fsVerityDigests:     make(map[string]string),
-		blobSize:            blobSize,
-		uncompressedTarSize: uncompressedTarSize,
+		pullOptions: pullOptions,
+		stream:      iss,
+		blobSize:    blobSize,
+
+		fileType: fileTypeZstdChunked,
+
 		tocDigest:           tocDigest,
-		copyBuffer:          makeCopyBuffer(),
-		fileType:            fileTypeZstdChunked,
-		layersCache:         layersCache,
+		tocOffset:           tocOffset,
 		manifest:            manifest,
 		toc:                 toc,
-		pullOptions:         pullOptions,
-		stream:              iss,
 		tarSplit:            tarSplit,
-		tocOffset:           tocOffset,
+		uncompressedTarSize: uncompressedTarSize,
+
+		layersCache:     layersCache,
+		copyBuffer:      makeCopyBuffer(),
+		fsVerityDigests: make(map[string]string),
 	}, false, nil
 }
 
@@ -354,17 +367,20 @@ func makeEstargzChunkedDiffer(store storage.Store, blobSize int64, tocDigest dig
 	}
 
 	return &chunkedDiffer{
-		fsVerityDigests:     make(map[string]string),
-		blobSize:            blobSize,
-		uncompressedTarSize: -1, // We would have to read and decompress the whole layer
+		pullOptions: pullOptions,
+		stream:      iss,
+		blobSize:    blobSize,
+
+		fileType: fileTypeEstargz,
+
 		tocDigest:           tocDigest,
-		copyBuffer:          makeCopyBuffer(),
-		fileType:            fileTypeEstargz,
-		layersCache:         layersCache,
-		manifest:            manifest,
-		pullOptions:         pullOptions,
-		stream:              iss,
 		tocOffset:           tocOffset,
+		manifest:            manifest,
+		uncompressedTarSize: -1, // We would have to read and decompress the whole layer
+
+		layersCache:     layersCache,
+		copyBuffer:      makeCopyBuffer(),
+		fsVerityDigests: make(map[string]string),
 	}, false, nil
 }