metropolis/pkg/erofs/erofs.go - monogon - Gitiles

 // Copyright 2020 The Monogon Project Authors.
 //
 // SPDX-License-Identifier: Apache-2.0
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.

 package erofs

 import (
 	"encoding/binary"
 	"errors"
 	"fmt"
 	"io"
 	"path"

 	"golang.org/x/sys/unix"
 )

 // Writer writes a new EROFS filesystem.
 type Writer struct {
 	w io.WriteSeeker
 	// fixDirectoryEntry contains for each referenced path where it is referenced from. Since self-references
 	// are required anyways (for the "." and ".." entries) we let the user write files in any order and just
 	// point the directory entries to the right target nid and file type on Close().
 	fixDirectoryEntry map[string][]direntFixupLocation
 	pathInodeMeta     map[string]*uncompressedInodeMeta
 	// legacyInodeIndex stores the next legacy (32-bit) inode to be allocated. 64 bit inodes are automatically
 	// calculated by EROFS on mount.
 	legacyInodeIndex    uint32
 	blockAllocatorIndex uint32
 	metadataBlocksFree  metadataBlocksMeta
 }

 // NewWriter creates a new EROFS filesystem writer. The given WriteSeeker needs to be at the start.
 func NewWriter(w io.WriteSeeker) (*Writer, error) {
 	erofsWriter := &Writer{
 		w:                 w,
 		fixDirectoryEntry: make(map[string][]direntFixupLocation),
 		pathInodeMeta:     make(map[string]*uncompressedInodeMeta),
 	}
 	_, err := erofsWriter.allocateMetadata(1024+binary.Size(&superblock{}), 0)
 	if err != nil {
 		return nil, fmt.Errorf("cannot allocate first metadata block: %w", err)
 	}
 	if _, err := erofsWriter.w.Write(make([]byte, 1024)); err != nil { // Padding
 		return nil, fmt.Errorf("failed to write initial padding: %w", err)
 	}
 	if err := binary.Write(erofsWriter.w, binary.LittleEndian, &superblock{
 		Magic:          Magic,
 		BlockSizeBits:  blockSizeBits,
 		RootNodeNumber: 36, // 1024 (padding) + 128 (superblock) / 32, not eligible for fixup as different int size
 	}); err != nil {
 		return nil, fmt.Errorf("failed to write superblock: %w", err)
 	}
 	return erofsWriter, nil
 }

 // allocateMetadata allocates metadata space of size bytes with a given alignment and seeks to the first byte of the
 // newly-allocated metadata space. It also returns the position of that first byte.
 func (w *Writer) allocateMetadata(size int, alignment uint16) (int64, error) {
 	if size > BlockSize {
 		panic("cannot allocate a metadata object bigger than BlockSize bytes")
 	}
 	sizeU16 := uint16(size)
 	pos, ok := w.metadataBlocksFree.findBlock(sizeU16, 32)
 	if !ok {
 		blockNumber, err := w.allocateBlocks(1)
 		if err != nil {
 			return 0, fmt.Errorf("failed to allocate additional metadata space: %w", err)
 		}
 		w.metadataBlocksFree = append(w.metadataBlocksFree, metadataBlockMeta{blockNumber: blockNumber, freeBytes: BlockSize - sizeU16})
 		if _, err := w.w.Write(make([]byte, BlockSize)); err != nil {
 			return 0, fmt.Errorf("failed to write metadata: %w", err)
 		}
 		pos = int64(blockNumber) * BlockSize // Always aligned to BlockSize, bigger alignments are unsupported anyways
 	}
 	if _, err := w.w.Seek(pos, io.SeekStart); err != nil {
 		return 0, fmt.Errorf("cannot seek to existing metadata nid, likely misaligned meta write")
 	}
 	return pos, nil
 }

 // allocateBlocks allocates n new BlockSize-sized block and seeks to the beginning of the first newly-allocated block.
 // It also returns the first newly-allocated block number.  The caller is expected to write these blocks completely
 // before calling allocateBlocks again.
 func (w *Writer) allocateBlocks(n uint32) (uint32, error) {
 	if _, err := w.w.Seek(int64(w.blockAllocatorIndex)*BlockSize, io.SeekStart); err != nil {
 		return 0, fmt.Errorf("cannot seek to end of last block, check write alignment: %w", err)
 	}
 	firstBlock := w.blockAllocatorIndex
 	w.blockAllocatorIndex += n
 	return firstBlock, nil
 }

 func (w *Writer) create(pathname string, inode Inode) *uncompressedInodeWriter {
 	i := &uncompressedInodeWriter{
 		writer:            w,
 		inode:             *inode.inode(),
 		legacyInodeNumber: w.legacyInodeIndex,
 		pathname:          path.Clean(pathname),
 	}
 	w.legacyInodeIndex++
 	return i
 }

 // CreateFile adds a new file to the EROFS. It returns a WriteCloser to which the file contents should be written and
 // which then needs to be closed. The last writer obtained by calling CreateFile() needs to be closed first before
 // opening a new one. The given pathname needs to be referenced by a directory created using Create(), otherwise it will
 // not be accessible.
 func (w *Writer) CreateFile(pathname string, meta *FileMeta) io.WriteCloser {
 	return w.create(pathname, meta)
 }

 // Create adds a new non-file inode to the EROFS. This includes directories, device nodes, symlinks and FIFOs.
 // The first call to Create() needs to be with pathname "." and a directory inode.
 // The given pathname needs to be referenced by a directory, otherwise it will not be accessible (with the exception of
 // the directory ".").
 func (w *Writer) Create(pathname string, inode Inode) error {
 	iw := w.create(pathname, inode)
 	switch i := inode.(type) {
 	case *Directory:
 		if err := i.writeTo(iw); err != nil {
 			return fmt.Errorf("failed to write directory contents: %w", err)
 		}
 	case *SymbolicLink:
 		if err := i.writeTo(iw); err != nil {
 			return fmt.Errorf("failed to write symbolic link contents: %w", err)
 		}
 	}
 	return iw.Close()
 }

 // Close finishes writing an EROFS filesystem. Errors by this function need to be handled as they indicate if the
 // written filesystem is consistent (i.e. there are no directory entries pointing to nonexistent inodes).
 func (w *Writer) Close() error {
 	for targetPath, entries := range w.fixDirectoryEntry {
 		for _, entry := range entries {
 			targetMeta, ok := w.pathInodeMeta[targetPath]
 			if !ok {
 				return fmt.Errorf("failed to link filesystem tree: dangling reference to %v", targetPath)
 			}
 			if err := direntFixup(w.pathInodeMeta[entry.path], int64(entry.entryIndex), targetMeta); err != nil {
 				return err
 			}
 		}
 	}
 	return nil
 }

 // uncompressedInodeMeta tracks enough metadata about a written inode to be able to point dirents to it and to provide
 // a WriteSeeker into the inode itself.
 type uncompressedInodeMeta struct {
 	nid   uint64
 	ftype uint8

 	// Physical placement metdata
 	blockStart   int64
 	blockLength  int64
 	inlineStart  int64
 	inlineLength int64

 	writer        *Writer
 	currentOffset int64
 }

 func (a *uncompressedInodeMeta) Seek(offset int64, whence int) (int64, error) {
 	switch whence {
 	case io.SeekCurrent:
 		break
 	case io.SeekStart:
 		a.currentOffset = 0
 	case io.SeekEnd:
 		a.currentOffset = a.blockLength + a.inlineLength
 	}
 	a.currentOffset += offset
 	return a.currentOffset, nil
 }

 func (a *uncompressedInodeMeta) Write(p []byte) (int, error) {
 	if a.currentOffset < a.blockLength {
 		// TODO(lorenz): Handle the special case where a directory inode is spread across multiple
 		// blocks (depending on other factors this occurs around ~200 direct children).
 		return 0, errors.New("relocating dirents in multi-block directory inodes is unimplemented")
 	}
 	if _, err := a.writer.w.Seek(a.inlineStart+a.currentOffset, io.SeekStart); err != nil {
 		return 0, err
 	}
 	a.currentOffset += int64(len(p))
 	return a.writer.w.Write(p)
 }

 type direntFixupLocation struct {
 	path       string
 	entryIndex uint16
 }

 // direntFixup overrides nid and file type from the path the dirent is pointing to. The given iw is expected to be at
 // the start of the dirent inode to be fixed up.
 func direntFixup(iw io.WriteSeeker, entryIndex int64, meta *uncompressedInodeMeta) error {
 	if _, err := iw.Seek(entryIndex*12, io.SeekStart); err != nil {
 		return fmt.Errorf("failed to seek to dirent: %w", err)
 	}
 	if err := binary.Write(iw, binary.LittleEndian, meta.nid); err != nil {
 		return fmt.Errorf("failed to write nid: %w", err)
 	}
 	if _, err := iw.Seek(2, io.SeekCurrent); err != nil { // Skip NameStartOffset
 		return fmt.Errorf("failed to seek to dirent: %w", err)
 	}
 	if err := binary.Write(iw, binary.LittleEndian, meta.ftype); err != nil {
 		return fmt.Errorf("failed to write ftype: %w", err)
 	}
 	return nil
 }

 type metadataBlockMeta struct {
 	blockNumber uint32
 	freeBytes   uint16
 }

 // metadataBlocksMeta contains metadata about all metadata blocks, most importantly the amount of free
 // bytes in each block. This is not a map for reproducibility (map ordering).
 type metadataBlocksMeta []metadataBlockMeta

 // findBlock returns the absolute position where `size` bytes with the specified alignment can still fit.
 // If there is not enough space in any metadata block it returns false as the second return value.
 func (m metadataBlocksMeta) findBlock(size uint16, alignment uint16) (int64, bool) {
 	for i, blockMeta := range m {
 		freeBytesAligned := blockMeta.freeBytes - (blockMeta.freeBytes % alignment)
 		if freeBytesAligned > size {
 			m[i] = metadataBlockMeta{
 				blockNumber: blockMeta.blockNumber,
 				freeBytes:   freeBytesAligned - size,
 			}
 			pos := int64(blockMeta.blockNumber+1)*BlockSize - int64(freeBytesAligned)
 			return pos, true
 		}
 	}
 	return 0, false
 }

 var unixModeToFTMap = map[uint16]uint8{
 	unix.S_IFREG:  fileTypeRegularFile,
 	unix.S_IFDIR:  fileTypeDirectory,
 	unix.S_IFCHR:  fileTypeCharacterDevice,
 	unix.S_IFBLK:  fileTypeBlockDevice,
 	unix.S_IFIFO:  fileTypeFIFO,
 	unix.S_IFSOCK: fileTypeSocket,
 	unix.S_IFLNK:  fileTypeSymbolicLink,
 }

 // unixModeToFT maps a Unix file type to an EROFS file type.
 func unixModeToFT(mode uint16) uint8 {
 	return unixModeToFTMap[mode&unix.S_IFMT]
 }
	// Copyright 2020 The Monogon Project Authors.
	//
	// SPDX-License-Identifier: Apache-2.0
	//
	// Licensed under the Apache License, Version 2.0 (the "License");
	// you may not use this file except in compliance with the License.
	// You may obtain a copy of the License at
	//
	// http://www.apache.org/licenses/LICENSE-2.0
	//
	// Unless required by applicable law or agreed to in writing, software
	// distributed under the License is distributed on an "AS IS" BASIS,
	// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	// See the License for the specific language governing permissions and
	// limitations under the License.

	package erofs

	import (
	"encoding/binary"
	"errors"
	"fmt"
	"io"
	"path"

	"golang.org/x/sys/unix"
	)

	// Writer writes a new EROFS filesystem.
	type Writer struct {
	w io.WriteSeeker
	// fixDirectoryEntry contains for each referenced path where it is referenced from. Since self-references
	// are required anyways (for the "." and ".." entries) we let the user write files in any order and just
	// point the directory entries to the right target nid and file type on Close().
	fixDirectoryEntry map[string][]direntFixupLocation
	pathInodeMeta map[string]*uncompressedInodeMeta
	// legacyInodeIndex stores the next legacy (32-bit) inode to be allocated. 64 bit inodes are automatically
	// calculated by EROFS on mount.
	legacyInodeIndex uint32
	blockAllocatorIndex uint32
	metadataBlocksFree metadataBlocksMeta
	}

	// NewWriter creates a new EROFS filesystem writer. The given WriteSeeker needs to be at the start.
	func NewWriter(w io.WriteSeeker) (*Writer, error) {
	erofsWriter := &Writer{
	w: w,
	fixDirectoryEntry: make(map[string][]direntFixupLocation),
	pathInodeMeta: make(map[string]*uncompressedInodeMeta),
	}
	_, err := erofsWriter.allocateMetadata(1024+binary.Size(&superblock{}), 0)
	if err != nil {
	return nil, fmt.Errorf("cannot allocate first metadata block: %w", err)
	}
	if _, err := erofsWriter.w.Write(make([]byte, 1024)); err != nil { // Padding
	return nil, fmt.Errorf("failed to write initial padding: %w", err)
	}
	if err := binary.Write(erofsWriter.w, binary.LittleEndian, &superblock{
	Magic: Magic,
	BlockSizeBits: blockSizeBits,
	RootNodeNumber: 36, // 1024 (padding) + 128 (superblock) / 32, not eligible for fixup as different int size
	}); err != nil {
	return nil, fmt.Errorf("failed to write superblock: %w", err)
	}
	return erofsWriter, nil
	}

	// allocateMetadata allocates metadata space of size bytes with a given alignment and seeks to the first byte of the
	// newly-allocated metadata space. It also returns the position of that first byte.
	func (w *Writer) allocateMetadata(size int, alignment uint16) (int64, error) {
	if size > BlockSize {
	panic("cannot allocate a metadata object bigger than BlockSize bytes")
	}
	sizeU16 := uint16(size)
	pos, ok := w.metadataBlocksFree.findBlock(sizeU16, 32)
	if !ok {
	blockNumber, err := w.allocateBlocks(1)
	if err != nil {
	return 0, fmt.Errorf("failed to allocate additional metadata space: %w", err)
	}
	w.metadataBlocksFree = append(w.metadataBlocksFree, metadataBlockMeta{blockNumber: blockNumber, freeBytes: BlockSize - sizeU16})
	if _, err := w.w.Write(make([]byte, BlockSize)); err != nil {
	return 0, fmt.Errorf("failed to write metadata: %w", err)
	}
	pos = int64(blockNumber) * BlockSize // Always aligned to BlockSize, bigger alignments are unsupported anyways
	}
	if _, err := w.w.Seek(pos, io.SeekStart); err != nil {
	return 0, fmt.Errorf("cannot seek to existing metadata nid, likely misaligned meta write")
	}
	return pos, nil
	}

	// allocateBlocks allocates n new BlockSize-sized block and seeks to the beginning of the first newly-allocated block.
	// It also returns the first newly-allocated block number. The caller is expected to write these blocks completely
	// before calling allocateBlocks again.
	func (w *Writer) allocateBlocks(n uint32) (uint32, error) {
	if _, err := w.w.Seek(int64(w.blockAllocatorIndex)*BlockSize, io.SeekStart); err != nil {
	return 0, fmt.Errorf("cannot seek to end of last block, check write alignment: %w", err)
	}
	firstBlock := w.blockAllocatorIndex
	w.blockAllocatorIndex += n
	return firstBlock, nil
	}

	func (w Writer) create(pathname string, inode Inode) uncompressedInodeWriter {
	i := &uncompressedInodeWriter{
	writer: w,
	inode: *inode.inode(),
	legacyInodeNumber: w.legacyInodeIndex,
	pathname: path.Clean(pathname),
	}
	w.legacyInodeIndex++
	return i
	}

	// CreateFile adds a new file to the EROFS. It returns a WriteCloser to which the file contents should be written and
	// which then needs to be closed. The last writer obtained by calling CreateFile() needs to be closed first before
	// opening a new one. The given pathname needs to be referenced by a directory created using Create(), otherwise it will
	// not be accessible.
	func (w Writer) CreateFile(pathname string, meta FileMeta) io.WriteCloser {
	return w.create(pathname, meta)
	}

	// Create adds a new non-file inode to the EROFS. This includes directories, device nodes, symlinks and FIFOs.
	// The first call to Create() needs to be with pathname "." and a directory inode.
	// The given pathname needs to be referenced by a directory, otherwise it will not be accessible (with the exception of
	// the directory ".").
	func (w *Writer) Create(pathname string, inode Inode) error {
	iw := w.create(pathname, inode)
	switch i := inode.(type) {
	case *Directory:
	if err := i.writeTo(iw); err != nil {
	return fmt.Errorf("failed to write directory contents: %w", err)
	}
	case *SymbolicLink:
	if err := i.writeTo(iw); err != nil {
	return fmt.Errorf("failed to write symbolic link contents: %w", err)
	}
	}
	return iw.Close()
	}

	// Close finishes writing an EROFS filesystem. Errors by this function need to be handled as they indicate if the
	// written filesystem is consistent (i.e. there are no directory entries pointing to nonexistent inodes).
	func (w *Writer) Close() error {
	for targetPath, entries := range w.fixDirectoryEntry {
	for _, entry := range entries {
	targetMeta, ok := w.pathInodeMeta[targetPath]
	if !ok {
	return fmt.Errorf("failed to link filesystem tree: dangling reference to %v", targetPath)
	}
	if err := direntFixup(w.pathInodeMeta[entry.path], int64(entry.entryIndex), targetMeta); err != nil {
	return err
	}
	}
	}
	return nil
	}

	// uncompressedInodeMeta tracks enough metadata about a written inode to be able to point dirents to it and to provide
	// a WriteSeeker into the inode itself.
	type uncompressedInodeMeta struct {
	nid uint64
	ftype uint8

	// Physical placement metdata
	blockStart int64
	blockLength int64
	inlineStart int64
	inlineLength int64

	writer *Writer
	currentOffset int64
	}

	func (a *uncompressedInodeMeta) Seek(offset int64, whence int) (int64, error) {
	switch whence {
	case io.SeekCurrent:
	break
	case io.SeekStart:
	a.currentOffset = 0
	case io.SeekEnd:
	a.currentOffset = a.blockLength + a.inlineLength
	}
	a.currentOffset += offset
	return a.currentOffset, nil
	}

	func (a *uncompressedInodeMeta) Write(p []byte) (int, error) {
	if a.currentOffset < a.blockLength {
	// TODO(lorenz): Handle the special case where a directory inode is spread across multiple
	// blocks (depending on other factors this occurs around ~200 direct children).
	return 0, errors.New("relocating dirents in multi-block directory inodes is unimplemented")
	}
	if _, err := a.writer.w.Seek(a.inlineStart+a.currentOffset, io.SeekStart); err != nil {
	return 0, err
	}
	a.currentOffset += int64(len(p))
	return a.writer.w.Write(p)
	}

	type direntFixupLocation struct {
	path string
	entryIndex uint16
	}

	// direntFixup overrides nid and file type from the path the dirent is pointing to. The given iw is expected to be at
	// the start of the dirent inode to be fixed up.
	func direntFixup(iw io.WriteSeeker, entryIndex int64, meta *uncompressedInodeMeta) error {
	if _, err := iw.Seek(entryIndex*12, io.SeekStart); err != nil {
	return fmt.Errorf("failed to seek to dirent: %w", err)
	}
	if err := binary.Write(iw, binary.LittleEndian, meta.nid); err != nil {
	return fmt.Errorf("failed to write nid: %w", err)
	}
	if _, err := iw.Seek(2, io.SeekCurrent); err != nil { // Skip NameStartOffset
	return fmt.Errorf("failed to seek to dirent: %w", err)
	}
	if err := binary.Write(iw, binary.LittleEndian, meta.ftype); err != nil {
	return fmt.Errorf("failed to write ftype: %w", err)
	}
	return nil
	}

	type metadataBlockMeta struct {
	blockNumber uint32
	freeBytes uint16
	}

	// metadataBlocksMeta contains metadata about all metadata blocks, most importantly the amount of free
	// bytes in each block. This is not a map for reproducibility (map ordering).
	type metadataBlocksMeta []metadataBlockMeta

	// findBlock returns the absolute position where `size` bytes with the specified alignment can still fit.
	// If there is not enough space in any metadata block it returns false as the second return value.
	func (m metadataBlocksMeta) findBlock(size uint16, alignment uint16) (int64, bool) {
	for i, blockMeta := range m {
	freeBytesAligned := blockMeta.freeBytes - (blockMeta.freeBytes % alignment)
	if freeBytesAligned > size {
	m[i] = metadataBlockMeta{
	blockNumber: blockMeta.blockNumber,
	freeBytes: freeBytesAligned - size,
	}
	pos := int64(blockMeta.blockNumber+1)*BlockSize - int64(freeBytesAligned)
	return pos, true
	}
	}
	return 0, false
	}

	var unixModeToFTMap = map[uint16]uint8{
	unix.S_IFREG: fileTypeRegularFile,
	unix.S_IFDIR: fileTypeDirectory,
	unix.S_IFCHR: fileTypeCharacterDevice,
	unix.S_IFBLK: fileTypeBlockDevice,
	unix.S_IFIFO: fileTypeFIFO,
	unix.S_IFSOCK: fileTypeSocket,
	unix.S_IFLNK: fileTypeSymbolicLink,
	}

	// unixModeToFT maps a Unix file type to an EROFS file type.
	func unixModeToFT(mode uint16) uint8 {
	return unixModeToFTMap[mode&unix.S_IFMT]
	}