btrfs: io4_fs.go: Subvolume: Don't have public members; use a constructor

3 files changed, 71 insertions, 58 deletions

diff --git a/cmd/btrfs-rec/inspect/mount/mount.go b/cmd/btrfs-rec/inspect/mount/mount.go
index 0e8faf1..4049393 100644
--- a/cmd/btrfs-rec/inspect/mount/mount.go
+++ b/cmd/btrfs-rec/inspect/mount/mount.go
@@ -28,6 +28,7 @@ import (
 	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs"
 	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsitem"
 	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsprim"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfstree"
 	"git.lukeshu.com/btrfs-progs-ng/lib/btrfsutil"
 	"git.lukeshu.com/btrfs-progs-ng/lib/containers"
 	"git.lukeshu.com/btrfs-progs-ng/lib/maps"
@@ -45,14 +46,21 @@ func MountRO(ctx context.Context, fs *btrfs.FS, mountpoint string, noChecksums b
 		deviceName = abs
 	}
 
+	sb, err := fs.Superblock()
+	if err != nil {
+		return err
+	}
+
 	rootSubvol := &subvolume{
-		Subvolume: btrfs.Subvolume{
-			FS:          btrfsutil.NewOldRebuiltForrest(ctx, fs),
-			TreeID:      btrfsprim.FS_TREE_OBJECTID,
-			NoChecksums: noChecksums,
-		},
+		Subvolume: btrfs.NewSubvolume(
+			btrfsutil.NewOldRebuiltForrest(ctx, fs),
+			btrfsprim.FS_TREE_OBJECTID,
+			noChecksums,
+		),
 		DeviceName: deviceName,
 		Mountpoint: mountpoint,
+
+		sb: sb,
 	}
 	return rootSubvol.Run(ctx)
 }
@@ -107,10 +115,12 @@ type fileState struct {
 }
 
 type subvolume struct {
-	btrfs.Subvolume
+	*btrfs.Subvolume
 	DeviceName string
 	Mountpoint string
 
+	sb *btrfstree.Superblock
+
 	fuseutil.NotImplementedFileSystem
 	lastHandle  uint64
 	dirHandles  typedsync.Map[fuseops.HandleID, *dirState]
@@ -189,11 +199,8 @@ func (sv *subvolume) LoadDir(inode btrfsprim.ObjID) (val *btrfs.Dir, err error)
 					workerName := fmt.Sprintf("%d-%s", val.Inode, filepath.Base(subMountpoint))
 					sv.grp.Go(workerName, func(ctx context.Context) error {
 						subSv := &subvolume{
-							Subvolume: btrfs.Subvolume{
-								FS:          sv.FS,
-								TreeID:      entry.Location.ObjectID,
-								NoChecksums: sv.NoChecksums,
-							},
+							sb:         sv.sb,
+							Subvolume:  sv.NewChildSubvolume(entry.Location.ObjectID),
 							DeviceName: sv.DeviceName,
 							Mountpoint: filepath.Join(sv.Mountpoint, subMountpoint[1:]),
 						}
@@ -208,11 +215,9 @@ func (sv *subvolume) LoadDir(inode btrfsprim.ObjID) (val *btrfs.Dir, err error)
 }
 
 func (sv *subvolume) StatFS(_ context.Context, op *fuseops.StatFSOp) error {
+	sb := sv.sb
+
 	// See linux.git/fs/btrfs/super.c:btrfs_statfs()
-	sb, err := sv.FS.Superblock()
-	if err != nil {
-		return err
-	}
 
 	op.IoSize = sb.SectorSize
 	op.BlockSize = sb.SectorSize
diff --git a/cmd/btrfs-rec/inspect_lsfiles.go b/cmd/btrfs-rec/inspect_lsfiles.go
index a2b46ab..e9fd057 100644
--- a/cmd/btrfs-rec/inspect_lsfiles.go
+++ b/cmd/btrfs-rec/inspect_lsfiles.go
@@ -45,10 +45,11 @@ func init() {
 			}()
 			ctx := cmd.Context()
 
-			printSubvol(out, "", true, "/", &btrfs.Subvolume{
-				FS:     btrfsutil.NewOldRebuiltForrest(ctx, fs),
-				TreeID: btrfsprim.FS_TREE_OBJECTID,
-			})
+			printSubvol(out, "", true, "/", btrfs.NewSubvolume(
+				btrfsutil.NewOldRebuiltForrest(ctx, fs),
+				btrfsprim.FS_TREE_OBJECTID,
+				false,
+			))
 
 			return nil
 		}),
@@ -160,10 +161,7 @@ func printDirEntry(out io.Writer, prefix string, isLast bool, subvol *btrfs.Subv
 			}
 			printDir(out, prefix, isLast, name, dir)
 		case btrfsitem.ROOT_ITEM_KEY:
-			printSubvol(out, prefix, isLast, name, &btrfs.Subvolume{
-				FS:     subvol.FS,
-				TreeID: entry.Location.ObjectID,
-			})
+			printSubvol(out, prefix, isLast, name, subvol.NewChildSubvolume(entry.Location.ObjectID))
 		default:
 			panic(fmt.Errorf("TODO: I don't know how to handle an FT_DIR with location.ItemType=%v: %q",
 				entry.Location.ItemType, name))
diff --git a/lib/btrfs/io4_fs.go b/lib/btrfs/io4_fs.go
index e4511a5..0445441 100644
--- a/lib/btrfs/io4_fs.go
+++ b/lib/btrfs/io4_fs.go
@@ -10,7 +10,6 @@ import (
 	"path/filepath"
 	"reflect"
 	"sort"
-	"sync"
 
 	"github.com/datawire/dlib/derror"
 
@@ -63,15 +62,13 @@ type File struct {
 }
 
 type Subvolume struct {
-	FS interface {
+	fs interface {
 		btrfstree.TreeOperator
 		Superblock() (*btrfstree.Superblock, error)
 		diskio.ReaderAt[btrfsvol.LogicalAddr]
 	}
 	TreeID      btrfsprim.ObjID
-	NoChecksums bool
-
-	initOnce sync.Once
+	noChecksums bool
 
 	rootVal btrfsitem.Root
 	rootErr error
@@ -82,41 +79,57 @@ type Subvolume struct {
 	fileCache      containers.ARCache[btrfsprim.ObjID, *File]
 }
 
-func (sv *Subvolume) init() {
-	sv.initOnce.Do(func() {
-		root, err := sv.FS.TreeSearch(btrfsprim.ROOT_TREE_OBJECTID, btrfstree.SearchRootItem(sv.TreeID))
-		if err != nil {
-			sv.rootErr = err
-		} else {
-			switch rootBody := root.Body.(type) {
-			case *btrfsitem.Root:
-				sv.rootVal = rootBody.Clone()
-			case *btrfsitem.Error:
-				sv.rootErr = fmt.Errorf("FS_TREE ROOT_ITEM has malformed body: %w", rootBody.Err)
-			default:
-				panic(fmt.Errorf("should not happen: ROOT_ITEM has unexpected item type: %T", rootBody))
-			}
+func NewSubvolume(
+	fs interface {
+		btrfstree.TreeOperator
+		Superblock() (*btrfstree.Superblock, error)
+		diskio.ReaderAt[btrfsvol.LogicalAddr]
+	},
+	treeID btrfsprim.ObjID,
+	noChecksums bool,
+) *Subvolume {
+	sv := &Subvolume{
+		fs:          fs,
+		TreeID:      treeID,
+		noChecksums: noChecksums,
+	}
+
+	root, err := sv.fs.TreeSearch(btrfsprim.ROOT_TREE_OBJECTID, btrfstree.SearchRootItem(sv.TreeID))
+	if err != nil {
+		sv.rootErr = err
+	} else {
+		switch rootBody := root.Body.(type) {
+		case *btrfsitem.Root:
+			sv.rootVal = rootBody.Clone()
+		case *btrfsitem.Error:
+			sv.rootErr = fmt.Errorf("FS_TREE ROOT_ITEM has malformed body: %w", rootBody.Err)
+		default:
+			panic(fmt.Errorf("should not happen: ROOT_ITEM has unexpected item type: %T", rootBody))
 		}
+	}
 
-		sv.bareInodeCache.MaxLen = textui.Tunable(128)
-		sv.fullInodeCache.MaxLen = textui.Tunable(128)
-		sv.dirCache.MaxLen = textui.Tunable(128)
-		sv.fileCache.MaxLen = textui.Tunable(128)
-	})
+	sv.bareInodeCache.MaxLen = textui.Tunable(128)
+	sv.fullInodeCache.MaxLen = textui.Tunable(128)
+	sv.dirCache.MaxLen = textui.Tunable(128)
+	sv.fileCache.MaxLen = textui.Tunable(128)
+
+	return sv
+}
+
+func (sv *Subvolume) NewChildSubvolume(childID btrfsprim.ObjID) *Subvolume {
+	return NewSubvolume(sv.fs, childID, sv.noChecksums)
 }
 
 func (sv *Subvolume) GetRootInode() (btrfsprim.ObjID, error) {
-	sv.init()
 	return sv.rootVal.RootDirID, sv.rootErr
 }
 
 func (sv *Subvolume) LoadBareInode(inode btrfsprim.ObjID) (*BareInode, error) {
-	sv.init()
 	val := containers.LoadOrElse[btrfsprim.ObjID, *BareInode](&sv.bareInodeCache, inode, func(inode btrfsprim.ObjID) (val *BareInode) {
 		val = &BareInode{
 			Inode: inode,
 		}
-		item, err := sv.FS.TreeLookup(sv.TreeID, btrfsprim.Key{
+		item, err := sv.fs.TreeLookup(sv.TreeID, btrfsprim.Key{
 			ObjectID: inode,
 			ItemType: btrfsitem.INODE_ITEM_KEY,
 			Offset:   0,
@@ -145,7 +158,6 @@ func (sv *Subvolume) LoadBareInode(inode btrfsprim.ObjID) (*BareInode, error) {
 }
 
 func (sv *Subvolume) LoadFullInode(inode btrfsprim.ObjID) (*FullInode, error) {
-	sv.init()
 	val := containers.LoadOrElse[btrfsprim.ObjID, *FullInode](&sv.fullInodeCache, inode, func(indoe btrfsprim.ObjID) (val *FullInode) {
 		val = &FullInode{
 			BareInode: BareInode{
@@ -153,7 +165,7 @@ func (sv *Subvolume) LoadFullInode(inode btrfsprim.ObjID) (*FullInode, error) {
 			},
 			XAttrs: make(map[string]string),
 		}
-		items, err := sv.FS.TreeSearchAll(sv.TreeID, btrfstree.SearchObject(inode))
+		items, err := sv.fs.TreeSearchAll(sv.TreeID, btrfstree.SearchObject(inode))
 		if err != nil {
 			val.Errs = append(val.Errs, err)
 			if len(items) == 0 {
@@ -200,7 +212,6 @@ func (sv *Subvolume) LoadFullInode(inode btrfsprim.ObjID) (*FullInode, error) {
 }
 
 func (sv *Subvolume) LoadDir(inode btrfsprim.ObjID) (*Dir, error) {
-	sv.init()
 	val := containers.LoadOrElse[btrfsprim.ObjID, *Dir](&sv.dirCache, inode, func(inode btrfsprim.ObjID) (val *Dir) {
 		val = new(Dir)
 		fullInode, err := sv.LoadFullInode(inode)
@@ -337,7 +348,6 @@ func (dir *Dir) AbsPath() (string, error) {
 }
 
 func (sv *Subvolume) LoadFile(inode btrfsprim.ObjID) (*File, error) {
-	sv.init()
 	val := containers.LoadOrElse[btrfsprim.ObjID, *File](&sv.fileCache, inode, func(inode btrfsprim.ObjID) (val *File) {
 		val = new(File)
 		fullInode, err := sv.LoadFullInode(inode)
@@ -449,7 +459,7 @@ func (file *File) maybeShortReadAt(dat []byte, off int64) (int, error) {
 		case btrfsitem.FILE_EXTENT_INLINE:
 			return copy(dat, extent.BodyInline[offsetWithinExt:offsetWithinExt+readSize]), nil
 		case btrfsitem.FILE_EXTENT_REG, btrfsitem.FILE_EXTENT_PREALLOC:
-			sb, err := file.SV.FS.Superblock()
+			sb, err := file.SV.fs.Superblock()
 			if err != nil {
 				return 0, err
 			}
@@ -458,7 +468,7 @@ func (file *File) maybeShortReadAt(dat []byte, off int64) (int, error) {
 				Add(btrfsvol.AddrDelta(offsetWithinExt))
 			var block [btrfssum.BlockSize]byte
 			blockBeg := (beg / btrfssum.BlockSize) * btrfssum.BlockSize
-			n, err := file.SV.FS.ReadAt(block[:], blockBeg)
+			n, err := file.SV.fs.ReadAt(block[:], blockBeg)
 			if n > int(beg-blockBeg) {
 				n = copy(dat[:readSize], block[beg-blockBeg:])
 			} else {
@@ -467,8 +477,8 @@ func (file *File) maybeShortReadAt(dat []byte, off int64) (int, error) {
 			if err != nil {
 				return 0, err
 			}
-			if !file.SV.NoChecksums {
-				sumRun, err := LookupCSum(file.SV.FS, sb.ChecksumType, blockBeg)
+			if !file.SV.noChecksums {
+				sumRun, err := LookupCSum(file.SV.fs, sb.ChecksumType, blockBeg)
 				if err != nil {
 					return 0, fmt.Errorf("checksum@%v: %w", blockBeg, err)
 				}