1 files changed, 411 insertions, 0 deletions
diff --git a/lib/btrfs/types_node.go b/lib/btrfs/types_node.go
new file mode 100644
index 0000000..5934f40
--- /dev/null
+++ b/lib/btrfs/types_node.go
@@ -0,0 +1,411 @@
+package btrfs
+
+import (
+	"encoding/binary"
+	"errors"
+	"fmt"
+
+	"git.lukeshu.com/btrfs-progs-ng/lib/binstruct"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsitem"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfssum"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsvol"
+	"git.lukeshu.com/btrfs-progs-ng/lib/util"
+)
+
+type NodeFlags uint64
+
+func (NodeFlags) BinaryStaticSize() int {
+	return 7
+}
+func (f NodeFlags) MarshalBinary() ([]byte, error) {
+	var bs [8]byte
+	binary.LittleEndian.PutUint64(bs[:], uint64(f))
+	return bs[:7], nil
+}
+func (f *NodeFlags) UnmarshalBinary(dat []byte) (int, error) {
+	var bs [8]byte
+	copy(bs[:7], dat[:7])
+	*f = NodeFlags(binary.LittleEndian.Uint64(bs[:]))
+	return 7, nil
+}
+
+var (
+	_ binstruct.StaticSizer = NodeFlags(0)
+	_ binstruct.Marshaler   = NodeFlags(0)
+	_ binstruct.Unmarshaler = (*NodeFlags)(nil)
+)
+
+const (
+	NodeWritten = NodeFlags(1 << iota)
+	NodeReloc
+)
+
+var nodeFlagNames = []string{
+	"WRITTEN",
+	"RELOC",
+}
+
+func (f NodeFlags) Has(req NodeFlags) bool { return f&req == req }
+func (f NodeFlags) String() string         { return util.BitfieldString(f, nodeFlagNames, util.HexLower) }
+
+type BackrefRev uint8
+
+const (
+	OldBackrefRev   = BackrefRev(iota)
+	MixedBackrefRev = BackrefRev(iota)
+)
+
+// Node: main //////////////////////////////////////////////////////////////////////////////////////
+
+type Node struct {
+	// Some context from the parent filesystem
+	Size         uint32            // superblock.NodeSize
+	ChecksumType btrfssum.CSumType // superblock.ChecksumType
+
+	// The node's header (always present)
+	Head NodeHeader
+
+	// The node's body (which one of these is present depends on
+	// the node's type, as specified in the header)
+	BodyInternal []KeyPointer // for internal nodes
+	BodyLeaf     []Item       // for leave nodes
+
+	Padding []byte
+}
+
+type NodeHeader struct {
+	Checksum      btrfssum.CSum        `bin:"off=0x0,  siz=0x20"`
+	MetadataUUID  UUID                 `bin:"off=0x20, siz=0x10"`
+	Addr          btrfsvol.LogicalAddr `bin:"off=0x30, siz=0x8"` // Logical address of this node
+	Flags         NodeFlags            `bin:"off=0x38, siz=0x7"`
+	BackrefRev    BackrefRev           `bin:"off=0x3f, siz=0x1"`
+	ChunkTreeUUID UUID                 `bin:"off=0x40, siz=0x10"`
+	Generation    Generation           `bin:"off=0x50, siz=0x8"`
+	Owner         ObjID                `bin:"off=0x58, siz=0x8"` // The ID of the tree that contains this node
+	NumItems      uint32               `bin:"off=0x60, siz=0x4"` // [ignored-when-writing]
+	Level         uint8                `bin:"off=0x64, siz=0x1"` // 0 for leaf nodes, >=1 for internal nodes
+	binstruct.End `bin:"off=0x65"`
+}
+
+// MaxItems returns the maximum possible valid value of
+// .Head.NumItems.
+func (node Node) MaxItems() uint32 {
+	bodyBytes := node.Size - uint32(binstruct.StaticSize(NodeHeader{}))
+	if node.Head.Level > 0 {
+		return bodyBytes / uint32(binstruct.StaticSize(KeyPointer{}))
+	} else {
+		return bodyBytes / uint32(binstruct.StaticSize(ItemHeader{}))
+	}
+}
+
+func (node Node) CalculateChecksum() (btrfssum.CSum, error) {
+	data, err := binstruct.Marshal(node)
+	if err != nil {
+		return btrfssum.CSum{}, err
+	}
+	return node.ChecksumType.Sum(data[binstruct.StaticSize(btrfssum.CSum{}):])
+}
+
+func (node Node) ValidateChecksum() error {
+	stored := node.Head.Checksum
+	calced, err := node.CalculateChecksum()
+	if err != nil {
+		return err
+	}
+	if calced != stored {
+		return fmt.Errorf("node checksum mismatch: stored=%v calculated=%v",
+			stored, calced)
+	}
+	return nil
+}
+
+func (node *Node) UnmarshalBinary(nodeBuf []byte) (int, error) {
+	*node = Node{
+		Size:         uint32(len(nodeBuf)),
+		ChecksumType: node.ChecksumType,
+	}
+	n, err := binstruct.Unmarshal(nodeBuf, &node.Head)
+	if err != nil {
+		return n, fmt.Errorf("btrfs.Node.UnmarshalBinary: %w", err)
+	}
+	if node.Head.Level > 0 {
+		_n, err := node.unmarshalInternal(nodeBuf[n:])
+		n += _n
+		if err != nil {
+			return n, fmt.Errorf("btrfs.Node.UnmarshalBinary: internal: %w", err)
+		}
+	} else {
+		_n, err := node.unmarshalLeaf(nodeBuf[n:])
+		n += _n
+		if err != nil {
+			return n, fmt.Errorf("btrfs.Node.UnmarshalBinary: leaf: %w", err)
+		}
+	}
+	if n != len(nodeBuf) {
+		return n, fmt.Errorf("btrfs.Node.UnmarshalBinary: left over data: got %v bytes but only consumed %v",
+			len(nodeBuf), n)
+	}
+	return n, nil
+}
+
+func (node Node) MarshalBinary() ([]byte, error) {
+	if node.Size == 0 {
+		return nil, fmt.Errorf("btrfs.Node.MarshalBinary: .Size must be set")
+	}
+	if node.Size <= uint32(binstruct.StaticSize(NodeHeader{})) {
+		return nil, fmt.Errorf("btrfs.Node.MarshalBinary: .Size must be greater than %v",
+			binstruct.StaticSize(NodeHeader{}))
+	}
+	if node.Head.Level > 0 {
+		node.Head.NumItems = uint32(len(node.BodyInternal))
+	} else {
+		node.Head.NumItems = uint32(len(node.BodyLeaf))
+	}
+
+	buf := make([]byte, node.Size)
+
+	if bs, err := binstruct.Marshal(node.Head); err != nil {
+		return buf, err
+	} else if len(bs) != binstruct.StaticSize(NodeHeader{}) {
+		return nil, fmt.Errorf("btrfs.Node.MarshalBinary: header is %v bytes but expected %v",
+			len(bs), binstruct.StaticSize(NodeHeader{}))
+	} else {
+		copy(buf, bs)
+	}
+
+	if node.Head.Level > 0 {
+		if err := node.marshalInternalTo(buf[binstruct.StaticSize(NodeHeader{}):]); err != nil {
+			return buf, err
+		}
+	} else {
+		if err := node.marshalLeafTo(buf[binstruct.StaticSize(NodeHeader{}):]); err != nil {
+			return buf, err
+		}
+	}
+
+	return buf, nil
+}
+
+// Node: "internal" ////////////////////////////////////////////////////////////////////////////////
+
+type KeyPointer struct {
+	Key           Key                  `bin:"off=0x0, siz=0x11"`
+	BlockPtr      btrfsvol.LogicalAddr `bin:"off=0x11, siz=0x8"`
+	Generation    Generation           `bin:"off=0x19, siz=0x8"`
+	binstruct.End `bin:"off=0x21"`
+}
+
+func (node *Node) unmarshalInternal(bodyBuf []byte) (int, error) {
+	n := 0
+	for i := uint32(0); i < node.Head.NumItems; i++ {
+		var item KeyPointer
+		_n, err := binstruct.Unmarshal(bodyBuf[n:], &item)
+		n += _n
+		if err != nil {
+			return n, fmt.Errorf("item %v: %w", i, err)
+		}
+		node.BodyInternal = append(node.BodyInternal, item)
+	}
+	node.Padding = bodyBuf[n:]
+	return len(bodyBuf), nil
+}
+
+func (node *Node) marshalInternalTo(bodyBuf []byte) error {
+	n := 0
+	for i, item := range node.BodyInternal {
+		bs, err := binstruct.Marshal(item)
+		if err != nil {
+			return fmt.Errorf("item %v: %w", i, err)
+		}
+		if copy(bodyBuf[n:], bs) < len(bs) {
+			return fmt.Errorf("item %v: not enough space: need at least %v+%v=%v bytes, but only have %v",
+				i, n, len(bs), n+len(bs), len(bodyBuf))
+		}
+		n += len(bs)
+	}
+	if copy(bodyBuf[n:], node.Padding) < len(node.Padding) {
+		return fmt.Errorf("padding: not enough space: need at least %v+%v=%v bytes, but only have %v",
+			n, len(node.Padding), n+len(node.Padding), len(bodyBuf))
+	}
+	return nil
+}
+
+// Node: "leaf" ////////////////////////////////////////////////////////////////////////////////////
+
+type Item struct {
+	Head ItemHeader
+	Body btrfsitem.Item
+}
+
+type ItemHeader struct {
+	Key           Key    `bin:"off=0x0, siz=0x11"`
+	DataOffset    uint32 `bin:"off=0x11, siz=0x4"` // [ignored-when-writing] relative to the end of the header (0x65)
+	DataSize      uint32 `bin:"off=0x15, siz=0x4"` // [ignored-when-writing]
+	binstruct.End `bin:"off=0x19"`
+}
+
+func (node *Node) unmarshalLeaf(bodyBuf []byte) (int, error) {
+	head := 0
+	tail := len(bodyBuf)
+	for i := uint32(0); i < node.Head.NumItems; i++ {
+		var item Item
+
+		n, err := binstruct.Unmarshal(bodyBuf[head:], &item.Head)
+		head += n
+		if err != nil {
+			return 0, fmt.Errorf("item %v: head: %w", i, err)
+		}
+		if head > tail {
+			return 0, fmt.Errorf("item %v: head: end_offset=%#x is in the body section (offset>%#x)",
+				i, head, tail)
+		}
+
+		dataOff := int(item.Head.DataOffset)
+		if dataOff < head {
+			return 0, fmt.Errorf("item %v: body: beg_offset=%#x is in the head section (offset<%#x)",
+				i, dataOff, head)
+		}
+		dataSize := int(item.Head.DataSize)
+		if dataOff+dataSize != tail {
+			return 0, fmt.Errorf("item %v: body: end_offset=%#x is not cur_tail=%#x)",
+				i, dataOff+dataSize, tail)
+		}
+		tail = dataOff
+		dataBuf := bodyBuf[dataOff : dataOff+dataSize]
+		item.Body = btrfsitem.UnmarshalItem(item.Head.Key, node.ChecksumType, dataBuf)
+
+		node.BodyLeaf = append(node.BodyLeaf, item)
+	}
+
+	node.Padding = bodyBuf[head:tail]
+	return len(bodyBuf), nil
+}
+
+func (node *Node) marshalLeafTo(bodyBuf []byte) error {
+	head := 0
+	tail := len(bodyBuf)
+	for i, item := range node.BodyLeaf {
+		itemBodyBuf, err := binstruct.Marshal(item.Body)
+		if err != nil {
+			return fmt.Errorf("item %v: body: %w", i, err)
+		}
+		item.Head.DataSize = uint32(len(itemBodyBuf))
+		item.Head.DataOffset = uint32(tail - len(itemBodyBuf))
+		itemHeadBuf, err := binstruct.Marshal(item.Head)
+		if err != nil {
+			return fmt.Errorf("item %v: head: %w", i, err)
+		}
+
+		if tail-head < len(itemHeadBuf)+len(itemBodyBuf) {
+			return fmt.Errorf("item %v: not enough space: need at least (head_len:%v)+(body_len:%v)=%v free bytes, but only have %v",
+				i, len(itemHeadBuf), len(itemBodyBuf), len(itemHeadBuf)+len(itemBodyBuf), tail-head)
+		}
+
+		copy(bodyBuf[head:], itemHeadBuf)
+		head += len(itemHeadBuf)
+		tail -= len(itemBodyBuf)
+		copy(bodyBuf[tail:], itemBodyBuf)
+	}
+	if copy(bodyBuf[head:tail], node.Padding) < len(node.Padding) {
+		return fmt.Errorf("padding: not enough space: need at least %v free bytes, but only have %v",
+			len(node.Padding), tail-head)
+	}
+	return nil
+}
+
+func (node *Node) LeafFreeSpace() uint32 {
+	if node.Head.Level > 0 {
+		panic(fmt.Errorf("Node.LeafFreeSpace: not a leaf node"))
+	}
+	freeSpace := node.Size
+	freeSpace -= uint32(binstruct.StaticSize(NodeHeader{}))
+	for _, item := range node.BodyLeaf {
+		freeSpace -= uint32(binstruct.StaticSize(ItemHeader{}))
+		freeSpace -= item.Head.DataSize
+	}
+	return freeSpace
+}
+
+// Tie Nodes in to the FS //////////////////////////////////////////////////////////////////////////
+
+var ErrNotANode = errors.New("does not look like a node")
+
+func ReadNode[Addr ~int64](fs util.File[Addr], sb Superblock, addr Addr, laddrCB func(btrfsvol.LogicalAddr) error) (*util.Ref[Addr, Node], error) {
+	nodeBuf := make([]byte, sb.NodeSize)
+	if _, err := fs.ReadAt(nodeBuf, addr); err != nil {
+		return nil, err
+	}
+
+	// parse (early)
+
+	nodeRef := &util.Ref[Addr, Node]{
+		File: fs,
+		Addr: addr,
+		Data: Node{
+			Size:         sb.NodeSize,
+			ChecksumType: sb.ChecksumType,
+		},
+	}
+	if _, err := binstruct.Unmarshal(nodeBuf, &nodeRef.Data.Head); err != nil {
+		return nodeRef, fmt.Errorf("btrfs.ReadNode: node@%v: %w", addr, err)
+	}
+
+	// sanity checking
+
+	if nodeRef.Data.Head.MetadataUUID != sb.EffectiveMetadataUUID() {
+		return nodeRef, fmt.Errorf("btrfs.ReadNode: node@%v: %w", addr, ErrNotANode)
+	}
+
+	stored := nodeRef.Data.Head.Checksum
+	calced, err := nodeRef.Data.ChecksumType.Sum(nodeBuf[binstruct.StaticSize(btrfssum.CSum{}):])
+	if err != nil {
+		return nodeRef, fmt.Errorf("btrfs.ReadNode: node@%v: %w", addr, err)
+	}
+	if stored != calced {
+		return nodeRef, fmt.Errorf("btrfs.ReadNode: node@%v: looks like a node but is corrupt: checksum mismatch: stored=%v calculated=%v",
+			addr, stored, calced)
+	}
+
+	if laddrCB != nil {
+		if err := laddrCB(nodeRef.Data.Head.Addr); err != nil {
+			return nodeRef, fmt.Errorf("btrfs.ReadNode: node@%v: %w", addr, err)
+		}
+	}
+
+	// parse (main)
+
+	if _, err := nodeRef.Data.UnmarshalBinary(nodeBuf); err != nil {
+		return nodeRef, fmt.Errorf("btrfs.ReadNode: node@%v: %w", addr, err)
+	}
+
+	// return
+
+	return nodeRef, nil
+}
+
+func (fs *FS) ReadNode(addr btrfsvol.LogicalAddr) (*util.Ref[btrfsvol.LogicalAddr, Node], error) {
+	sb, err := fs.Superblock()
+	if err != nil {
+		return nil, fmt.Errorf("btrfs.FS.ReadNode: %w", err)
+	}
+
+	return ReadNode[btrfsvol.LogicalAddr](fs, sb.Data, addr, func(claimAddr btrfsvol.LogicalAddr) error {
+		if claimAddr != addr {
+			return fmt.Errorf("read from laddr=%v but claims to be at laddr=%v",
+				addr, claimAddr)
+		}
+		return nil
+	})
+}
+
+func (fs *FS) readNodeAtLevel(addr btrfsvol.LogicalAddr, expLevel uint8) (*util.Ref[btrfsvol.LogicalAddr, Node], error) {
+	node, err := fs.ReadNode(addr)
+	if err != nil {
+		return node, err
+	}
+	if node.Data.Head.Level != expLevel {
+		return node, fmt.Errorf("btrfs.FS.ReadNode: node@%v: expected level %v but has level %v",
+			node.Addr, expLevel, node.Data.Head.Level)
+	}
+	return node, nil
+}