1 files changed, 196 insertions, 0 deletions
diff --git a/cmd/btrfs-mount/subvol_fuse.go b/cmd/btrfs-mount/subvol_fuse.go
new file mode 100644
index 0000000..6ffc7d6
--- /dev/null
+++ b/cmd/btrfs-mount/subvol_fuse.go
@@ -0,0 +1,196 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"sync/atomic"
+	"syscall"
+
+	"github.com/jacobsa/fuse/fuseops"
+	"github.com/jacobsa/fuse/fuseutil"
+
+	"lukeshu.com/btrfs-tools/pkg/btrfs"
+	"lukeshu.com/btrfs-tools/pkg/btrfs/btrfsitem"
+	"lukeshu.com/btrfs-tools/pkg/util"
+)
+
+type dirState struct {
+	Dir *dir
+}
+
+type subvolumeFUSE struct {
+	fuseutil.NotImplementedFileSystem
+	lastHandle uint64
+	dirHandles util.SyncMap[uint64, *dirState]
+}
+
+func (sv *subvolumeFUSE) init() {}
+
+func inodeItemToFUSE(itemBody btrfsitem.Inode) fuseops.InodeAttributes {
+	return fuseops.InodeAttributes{
+		Size:  uint64(itemBody.Size),
+		Nlink: uint32(itemBody.NLink),
+		Mode:  uint32(itemBody.Mode),
+		//RDev: itemBody.Rdev, // jacobsa/fuse doesn't expose rdev
+		Atime: itemBody.ATime.ToStd(),
+		Mtime: itemBody.MTime.ToStd(),
+		Ctime: itemBody.CTime.ToStd(),
+		//Crtime: itemBody.OTime,
+		Uid: uint32(itemBody.UID),
+		Gid: uint32(itemBody.GID),
+	}
+}
+
+func (sv *Subvolume) StatFS(_ context.Context, op *fuseops.StatFSOp) error {
+	// See linux.git/fs/btrfs/super.c:btrfs_statfs()
+	sb, err := sv.FS.Superblock()
+	if err != nil {
+		return err
+	}
+
+	op.IoSize = sb.Data.SectorSize
+	op.BlockSize = sb.Data.SectorSize
+	op.Blocks = sb.Data.TotalBytes / uint64(sb.Data.SectorSize) // TODO: adjust for RAID type
+	//op.BlocksFree = TODO
+
+	// btrfs doesn't have a fixed number of inodes
+	op.Inodes = 0
+	op.InodesFree = 0
+
+	// jacobsa/fuse doesn't expose namelen, instead hard-coding it
+	// to 255.  Which is fine by us, because that's what it is for
+	// btrfs.
+
+	return nil
+}
+
+func (sv *Subvolume) LookUpInode(_ context.Context, op *fuseops.LookUpInodeOp) error {
+	if op.Parent == fuseops.RootInodeID {
+		parent, err := sv.getRootInode()
+		if err != nil {
+			return err
+		}
+		op.Parent = fuseops.InodeID(parent)
+	}
+
+	dir, err := sv.loadDir(btrfs.ObjID(op.Parent))
+	if err != nil {
+		return err
+	}
+	entry, ok := dir.ChildrenByName[op.Name]
+	if !ok {
+		return syscall.ENOENT
+	}
+	if entry.Location.ItemType != btrfsitem.INODE_ITEM_KEY {
+		return fmt.Errorf("child %q is not an inode: %w", op.Name, syscall.ENOSYS)
+	}
+	inodeItem, err := sv.loadInode(entry.Location.ObjectID)
+	if err != nil {
+		return err
+	}
+	op.Entry = fuseops.ChildInodeEntry{
+		Child:      fuseops.InodeID(entry.Location.ObjectID),
+		Generation: fuseops.GenerationNumber(inodeItem.Sequence),
+		Attributes: inodeItemToFUSE(inodeItem),
+	}
+	return nil
+}
+
+func (sv *Subvolume) GetInodeAttributes(_ context.Context, op *fuseops.GetInodeAttributesOp) error {
+	if op.Inode == fuseops.RootInodeID {
+		inode, err := sv.getRootInode()
+		if err != nil {
+			return err
+		}
+		op.Inode = fuseops.InodeID(inode)
+	}
+
+	inodeItem, err := sv.loadInode(btrfs.ObjID(op.Inode))
+	if err != nil {
+		return err
+	}
+
+	op.Attributes = inodeItemToFUSE(inodeItem)
+	return nil
+}
+
+func (sv *Subvolume) OpenDir(_ context.Context, op *fuseops.OpenDirOp) error {
+	if op.Inode == fuseops.RootInodeID {
+		inode, err := sv.getRootInode()
+		if err != nil {
+			return err
+		}
+		op.Inode = fuseops.InodeID(inode)
+	}
+
+	dir, err := sv.loadDir(btrfs.ObjID(op.Inode))
+	if err != nil {
+		return err
+	}
+	handle := atomic.AddUint64(&sv.lastHandle, 1)
+	sv.dirHandles.Store(handle, &dirState{
+		Dir: dir,
+	})
+	op.Handle = fuseops.HandleID(handle)
+	return nil
+}
+
+func (sv *Subvolume) ReadDir(_ context.Context, op *fuseops.ReadDirOp) error {
+	state, ok := sv.dirHandles.Load(uint64(op.Handle))
+	if !ok {
+		return syscall.EBADF
+	}
+	indexes := util.SortedMapKeys(state.Dir.ChildrenByIndex)
+	origOffset := op.Offset
+	for _, index := range indexes {
+		if index < uint64(origOffset) {
+			continue
+		}
+		entry := state.Dir.ChildrenByIndex[index]
+		n := fuseutil.WriteDirent(op.Dst[op.BytesRead:], fuseutil.Dirent{
+			Offset: fuseops.DirOffset(index + 1),
+			Inode:  fuseops.InodeID(entry.Location.ObjectID),
+			Name:   string(entry.Name),
+			Type: map[btrfsitem.FileType]fuseutil.DirentType{
+				btrfsitem.FT_UNKNOWN:  fuseutil.DT_Unknown,
+				btrfsitem.FT_REG_FILE: fuseutil.DT_File,
+				btrfsitem.FT_DIR:      fuseutil.DT_Directory,
+				btrfsitem.FT_CHRDEV:   fuseutil.DT_Char,
+				btrfsitem.FT_BLKDEV:   fuseutil.DT_Block,
+				btrfsitem.FT_FIFO:     fuseutil.DT_FIFO,
+				btrfsitem.FT_SOCK:     fuseutil.DT_Socket,
+				btrfsitem.FT_SYMLINK:  fuseutil.DT_Link,
+			}[entry.Type],
+		})
+		if n == 0 {
+			break
+		}
+		op.BytesRead += n
+	}
+	return nil
+}
+
+func (sv *Subvolume) ReleaseDirHandle(_ context.Context, op *fuseops.ReleaseDirHandleOp) error {
+	_, ok := sv.dirHandles.LoadAndDelete(uint64(op.Handle))
+	if !ok {
+		return syscall.EBADF
+	}
+	return nil
+}
+
+func (sv *Subvolume) OpenFile(_ context.Context, op *fuseops.OpenFileOp) error { return syscall.ENOSYS }
+func (sv *Subvolume) ReadFile(_ context.Context, op *fuseops.ReadFileOp) error { return syscall.ENOSYS }
+func (sv *Subvolume) ReleaseFileHandle(_ context.Context, op *fuseops.ReleaseFileHandleOp) error {
+	return syscall.ENOSYS
+}
+
+func (sv *Subvolume) ReadSymlink(_ context.Context, op *fuseops.ReadSymlinkOp) error {
+	return syscall.ENOSYS
+}
+
+func (sv *Subvolume) GetXattr(_ context.Context, op *fuseops.GetXattrOp) error { return syscall.ENOSYS }
+func (sv *Subvolume) ListXattr(_ context.Context, op *fuseops.ListXattrOp) error {
+	return syscall.ENOSYS
+}
+
+func (sv *Subvolume) Destroy() {}