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// Copyright (C) 2022-2023 Luke Shumaker <lukeshu@lukeshu.com>
//
// SPDX-License-Identifier: GPL-2.0-or-later
package btrfstree
import (
"context"
"fmt"
"strings"
"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsprim"
"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsvol"
"git.lukeshu.com/btrfs-progs-ng/lib/containers"
"git.lukeshu.com/btrfs-progs-ng/lib/slices"
)
// Path is a path from the superblock or a ROOT_ITEM to a node or
// item within one of the btrees in the system.
//
// - The first element will always have a FromSlot of -1.
//
// - For .Item() callbacks, the last element will always have a
// NodeAddr of 0.
//
// For example, a path through a tree, with the associated PathElems:
//
// [superblock: tree=B, lvl=3, gen=6]
// |
// | <------------------------------------------ PathRoot={Tree:B,
// | ToAddr:0x01, ToGen=6, ToLvl=3}
// +[0x01]-------------+
// | lvl=3 gen=6 own=B |
// +-+-+-+-+-+-+-+-+-+-+
// |0|1|2|3|4|5|6|7|8|9|
// +-+-+-+-+-+-+-+-+-+-+
// |
// | <------------------------------ PathKP={FromTree:B, FromSlot:7,
// | ToAddr:0x02, ToGen:5, ToLvl:2}
// +[0x02]--------------+
// | lvl=2 gen=5 own=B |
// +-+-+-+-+-+-+-+-+-+-+
// |0|1|2|3|4|5|6|7|8|9|
// +-+-+-+-+-+-+-+-+-+-+
// |
// | <-------------------- PathKP={FromTree:B, FromSlot:6,
// | ToAddr:0x03, ToGen:5, ToLvl:1}
// +[0x03]-------------+
// | lvl=1 gen=5 own=A |
// +-+-+-+-+-+-+-+-+-+-+
// |0|1|2|3|4|5|6|7|8|9|
// +-+-+-+-+-+-+-+-+-+-+
// |
// | <---------------- PathKP={FromTree:A, FromSlot:3,
// | ToAddr:0x04, ToGen:2, ToLvl:0}
// +[0x04]-------------+
// | lvl=0 gen=2 own=A |
// +-+-+-+-+-+-+-+-+-+-+
// |0|1|2|3|4|5|6|7|8|9|
// +-+-+-+-+-+-+-+-+-+-+
// |
// | <--------------- PathItem={FromTree:A, FromSlot:1}
// |
// [item]
type Path []PathElem
// A PathElem is either a PathRoot, a PathKP, or a PathItem.
type PathElem interface {
isPathElem()
}
type PathRoot struct {
Forrest Forrest
// It should be no surprise that these 4 members mimic the 4
// members of a 'RawTree'.
TreeID btrfsprim.ObjID
ToAddr btrfsvol.LogicalAddr
ToGeneration btrfsprim.Generation
ToLevel uint8
}
func (PathRoot) isPathElem() {}
type PathKP struct {
// From the containing Node.
FromTree btrfsprim.ObjID
FromSlot int
// From the KP itself.
ToAddr btrfsvol.LogicalAddr
ToGeneration btrfsprim.Generation
ToMinKey btrfsprim.Key
// From the structure of the tree.
ToMaxKey btrfsprim.Key
ToLevel uint8
}
func (PathKP) isPathElem() {}
type PathItem struct {
// From the containing Node.
FromTree btrfsprim.ObjID
FromSlot int
// From the Item itself.
ToKey btrfsprim.Key
}
func (PathItem) isPathElem() {}
func (path Path) String() string {
if len(path) == 0 {
return "(empty-path)"
}
var ret strings.Builder
for _, elem := range path {
switch elem := elem.(type) {
case PathRoot:
fmt.Fprintf(&ret, "%s->node:%d@%v",
elem.TreeID.Format(btrfsprim.ROOT_TREE_OBJECTID),
elem.ToLevel, elem.ToAddr)
case PathKP:
fmt.Fprintf(&ret, "[%d]->node:%d@%v",
elem.FromSlot,
elem.ToLevel, elem.ToAddr)
case PathItem:
// fmt.Fprintf(&ret, "[%d]->item:%v",
// elem.FromSlot,
// elem.ToKey)
fmt.Fprintf(&ret, "[%d]",
elem.FromSlot)
default:
panic(fmt.Errorf("should not happen: unexpected PathElem type: %T", elem))
}
}
return ret.String()
}
func checkOwner(
ctx context.Context, forrest Forrest, treeID btrfsprim.ObjID,
ownerToCheck btrfsprim.ObjID, genToCheck btrfsprim.Generation,
) error {
var stack []btrfsprim.ObjID
for {
if ownerToCheck == treeID {
return nil
}
tree, err := forrest.ForrestLookup(ctx, treeID)
if err != nil {
return fmt.Errorf("unable to determine whether owner=%v generation=%v is acceptable: %w",
ownerToCheck, genToCheck, err)
}
parentID, parentGen, err := tree.TreeParentID(ctx)
if err != nil {
return fmt.Errorf("unable to determine whether owner=%v generation=%v is acceptable: %w",
ownerToCheck, genToCheck, err)
}
stack = append(stack, treeID)
if slices.Contains(parentID, stack) {
// Don't get stuck in an infinite loop if there's a cycle.
parentID = 0
}
if parentID == 0 && parentGen == 0 {
return fmt.Errorf("owner=%v is not acceptable in this tree",
ownerToCheck)
}
if genToCheck > parentGen {
return fmt.Errorf("claimed owner=%v might be acceptable in this tree (if generation<=%v) but not with claimed generation=%v",
ownerToCheck, parentGen, genToCheck)
}
treeID = parentID
}
}
// NodeExpectations returns the address to read and the expectations
// to have when reading the node pointed to by this Path.
//
// `ok` is false if the path is empty or if this Path points to an
// item rather than a node.
func (path Path) NodeExpectations(ctx context.Context) (_ btrfsvol.LogicalAddr, _ NodeExpectations, ok bool) {
if len(path) == 0 {
return 0, NodeExpectations{}, false
}
firstElem, ok := path[0].(PathRoot)
if !ok {
panic(fmt.Errorf("should not happen: first PathElem is not PathRoot: %T", path[0]))
}
switch lastElem := path[len(path)-1].(type) {
case PathRoot:
return lastElem.ToAddr, NodeExpectations{
LAddr: containers.OptionalValue(lastElem.ToAddr),
Level: containers.OptionalValue(lastElem.ToLevel),
Generation: containers.OptionalValue(lastElem.ToGeneration),
Owner: func(owner btrfsprim.ObjID, gen btrfsprim.Generation) error {
return checkOwner(ctx, firstElem.Forrest, lastElem.TreeID,
owner, gen)
},
MinItem: containers.OptionalValue(btrfsprim.Key{}),
MaxItem: containers.OptionalValue(btrfsprim.MaxKey),
}, true
case PathKP:
return lastElem.ToAddr, NodeExpectations{
LAddr: containers.OptionalValue(lastElem.ToAddr),
Level: containers.OptionalValue(lastElem.ToLevel),
Generation: containers.OptionalValue(lastElem.ToGeneration),
Owner: func(owner btrfsprim.ObjID, gen btrfsprim.Generation) error {
return checkOwner(ctx, firstElem.Forrest, lastElem.FromTree,
owner, gen)
},
MinItem: containers.OptionalValue(lastElem.ToMinKey),
MaxItem: containers.OptionalValue(lastElem.ToMaxKey),
}, true
case PathItem:
return 0, NodeExpectations{}, false
default:
panic(fmt.Errorf("should not happen: unexpected PathElem type: %T", lastElem))
}
}
func (path Path) Parent() Path {
return path[:len(path)-1]
}
|
