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package btrfs
import (
"errors"
"fmt"
"io"
iofs "io/fs"
"math"
"strings"
"lukeshu.com/btrfs-tools/pkg/btrfs/btrfsitem"
"lukeshu.com/btrfs-tools/pkg/util"
)
// A TreePathElem essentially represents a KeyPointer.
type TreePathElem struct {
// ItemIdx is the index of this KeyPointer in the parent Node;
// or -1 if this is the root and there is no KeyPointer.
ItemIdx int
// NodeAddr is the address of the node that the KeyPointer
// points at, or 0 if this is a leaf item and nothing is
// being pointed at.
NodeAddr LogicalAddr
// NodeLevel is the expected or actual level of the node at
// NodeAddr, or 255 if there is no knowledge of the level.
NodeLevel uint8
}
func (elem TreePathElem) writeNodeTo(w io.Writer) {
if elem.NodeLevel != math.MaxUint8 {
fmt.Fprintf(w, "node:%d@%v", elem.NodeLevel, elem.NodeAddr)
} else {
fmt.Fprintf(w, "node@%v", elem.NodeAddr)
}
}
// - The first element will always have an ItemIdx of -1.
//
// - For .Item() callbacks, the last element will always have a
// NodeAddr of 0.
type TreePath []TreePathElem
func (path TreePath) String() string {
if len(path) == 0 {
return "(empty-path)"
}
var ret strings.Builder
path[0].writeNodeTo(&ret)
for _, elem := range path[1:] {
fmt.Fprintf(&ret, "[%v]", elem.ItemIdx)
if elem.NodeAddr != 0 {
ret.WriteString("->")
elem.writeNodeTo(&ret)
}
}
return ret.String()
}
type TreeWalkHandler struct {
// Callbacks for entire nodes
PreNode func(TreePath) error
Node func(TreePath, *util.Ref[LogicalAddr, Node], error) error
PostNode func(TreePath, *util.Ref[LogicalAddr, Node]) error
// Callbacks for items on internal nodes
PreKeyPointer func(TreePath, KeyPointer) error
PostKeyPointer func(TreePath, KeyPointer) error
// Callbacks for items on leaf nodes
Item func(TreePath, Item) error
}
// The lifecycle of callbacks is:
//
// 001 .PreNode()
// 002 (read node)
// 003 .Node()
// for item in node.items:
// if internal:
// 004 .PreKeyPointer()
// 005 (recurse)
// 006 .PostKeyPointer()
// else:
// 004 .Item()
// 007 .PostNode()
func (fs *FS) TreeWalk(treeRoot LogicalAddr, cbs TreeWalkHandler) error {
path := TreePath{
TreePathElem{
ItemIdx: -1,
NodeAddr: treeRoot,
NodeLevel: math.MaxUint8,
},
}
return fs.treeWalk(path, cbs)
}
func (fs *FS) treeWalk(path TreePath, cbs TreeWalkHandler) error {
if path[len(path)-1].NodeAddr == 0 {
return nil
}
if cbs.PreNode != nil {
if err := cbs.PreNode(path); err != nil {
if errors.Is(err, iofs.SkipDir) {
return nil
}
return err
}
}
node, err := fs.ReadNode(path[len(path)-1].NodeAddr)
if node != nil {
if exp := path[len(path)-1].NodeLevel; exp != math.MaxUint8 && node.Data.Head.Level != exp && err == nil {
err = fmt.Errorf("btrfs.FS.TreeWalk: node@%v: expected level %v but has level %v",
node.Addr, exp, node.Data.Head.Level)
}
path[len(path)-1].NodeLevel = node.Data.Head.Level
}
if cbs.Node != nil {
err = cbs.Node(path, node, err)
}
if err != nil {
if errors.Is(err, iofs.SkipDir) {
return nil
}
return fmt.Errorf("btrfs.FS.TreeWalk: %w", err)
}
if node != nil {
for i, item := range node.Data.BodyInternal {
itemPath := append(path, TreePathElem{
ItemIdx: i,
NodeAddr: item.BlockPtr,
NodeLevel: node.Data.Head.Level - 1,
})
if cbs.PreKeyPointer != nil {
if err := cbs.PreKeyPointer(itemPath, item); err != nil {
if errors.Is(err, iofs.SkipDir) {
continue
}
return err
}
}
if err := fs.treeWalk(itemPath, cbs); err != nil {
return err
}
if cbs.PostKeyPointer != nil {
if err := cbs.PostKeyPointer(itemPath, item); err != nil {
if errors.Is(err, iofs.SkipDir) {
continue
}
return err
}
}
}
for i, item := range node.Data.BodyLeaf {
if cbs.Item != nil {
itemPath := append(path, TreePathElem{
ItemIdx: i,
})
if err := cbs.Item(itemPath, item); err != nil {
if errors.Is(err, iofs.SkipDir) {
continue
}
return fmt.Errorf("btrfs.FS.TreeWalk: callback: %w", err)
}
}
}
}
if cbs.PostNode != nil {
if err := cbs.PostNode(path, node); err != nil {
if errors.Is(err, iofs.SkipDir) {
return nil
}
return err
}
}
return nil
}
func (fs *FS) TreeSearch(treeRoot LogicalAddr, fn func(Key) int) (Key, btrfsitem.Item, error) {
nodeAddr := treeRoot
for {
if nodeAddr == 0 {
return Key{}, nil, iofs.ErrNotExist
}
node, err := fs.ReadNode(nodeAddr)
if err != nil {
return Key{}, nil, err
}
if node.Data.Head.Level > 0 {
// internal node
// Search for the right-most node.Data.BodyInternal item for which
// `fn(item.Key) >= 0`.
//
// + + + + 0 - - - -
//
// There may or may not be a value that returns '0'.
//
// Implement this search as a binary search.
lastGood := -1
firstBad := len(node.Data.BodyInternal)
for firstBad > lastGood+1 {
midpoint := (lastGood + firstBad) / 2
direction := fn(node.Data.BodyInternal[midpoint].Key)
if direction < 0 {
firstBad = midpoint
} else {
lastGood = midpoint
}
}
if lastGood < 0 {
return Key{}, nil, iofs.ErrNotExist
}
nodeAddr = node.Data.BodyInternal[lastGood].BlockPtr
} else {
// leaf node
// Search for a member of node.Data.BodyLeaf for which
// `fn(item.Head.Key) == 0`.
//
// + + + + 0 - - - -
//
// Such an item might not exist; in this case, return nil/ErrNotExist.
// Multiple such items might exist; in this case, it does not matter which
// is returned.
//
// Implement this search as a binary search.
items := node.Data.BodyLeaf
for len(items) > 0 {
midpoint := len(items) / 2
direction := fn(items[midpoint].Head.Key)
switch {
case direction < 0:
items = items[:midpoint]
case direction > 0:
items = items[midpoint+1:]
case direction == 0:
return items[midpoint].Head.Key, items[midpoint].Body, nil
}
}
return Key{}, nil, iofs.ErrNotExist
}
}
}
func (fs *FS) TreeLookup(treeRoot LogicalAddr, key Key) (Key, btrfsitem.Item, error) {
return fs.TreeSearch(treeRoot, key.Cmp)
}
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