btrfstree: Distinguish between tree-not-found and item-not-found

5 files changed, 108 insertions, 5 deletions

diff --git a/lib/btrfs/btrfstree/btree.go b/lib/btrfs/btrfstree/btree.go
index 2fd7c39..7b3721b 100644
--- a/lib/btrfs/btrfstree/btree.go
+++ b/lib/btrfs/btrfstree/btree.go
@@ -45,7 +45,10 @@ type TreeOperator interface {
 	// If some items are able to be read, but there is an error reading the
 	// full set, then it might return *both* a list of items and an error.
 	//
-	// If no such item is found, an error that is io/fs.ErrNotExist is
+	// If the tree is not found, an error that is ErrNoTree is
+	// returned.
+	//
+	// If no such item is found, an error that is ErrNoItem is
 	// returned.
 	TreeSearchAll(treeID btrfsprim.ObjID, fn func(key btrfsprim.Key, size uint32) int) ([]Item, error) // size is math.MaxUint32 for key-pointers
 }
diff --git a/lib/btrfs/btrfstree/btree_err.go b/lib/btrfs/btrfstree/btree_err.go
new file mode 100644
index 0000000..57fb283
--- /dev/null
+++ b/lib/btrfs/btrfstree/btree_err.go
@@ -0,0 +1,32 @@
+// Copyright (C) 2023  Luke Shumaker <lukeshu@lukeshu.com>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+package btrfstree
+
+import (
+	iofs "io/fs"
+)
+
+// For both ErrNoItem and ErrNoTree, `errors.Is(err,
+// io/fs.ErrNotExist)` returns true.
+var (
+	ErrNoItem = errNotExist("item")
+	ErrNoTree = errNotExist("tree")
+)
+
+func errNotExist(thing string) error {
+	return &notExistError{thing}
+}
+
+type notExistError struct {
+	thing string
+}
+
+func (e *notExistError) Error() string {
+	return e.thing + " does not exist"
+}
+
+func (*notExistError) Is(target error) bool {
+	return target == iofs.ErrNotExist
+}
diff --git a/lib/btrfs/btrfstree/btree_err_test.go b/lib/btrfs/btrfstree/btree_err_test.go
new file mode 100644
index 0000000..381bd56
--- /dev/null
+++ b/lib/btrfs/btrfstree/btree_err_test.go
@@ -0,0 +1,64 @@
+// Copyright (C) 2023  Luke Shumaker <lukeshu@lukeshu.com>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+package btrfstree_test
+
+import (
+	"errors"
+	"fmt"
+	iofs "io/fs"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfstree"
+)
+
+func TestErrs(t *testing.T) {
+	t.Parallel()
+
+	errItem := fmt.Errorf("my item: %w", btrfstree.ErrNoItem)
+	errTree := fmt.Errorf("my tree: %w", btrfstree.ErrNoTree)
+
+	// 1. errItem
+	// 2. errTree
+	// 3. btrfstree.ErrNoItem
+	// 4. btrfstree.ErrNoTree
+	// 5. iofs.ErrNotExist
+
+	// 1
+	assert.Equal(t, errors.Is(errItem, errItem), true)
+	assert.Equal(t, errors.Is(errItem, errTree), false)
+	assert.Equal(t, errors.Is(errItem, btrfstree.ErrNoItem), true)
+	assert.Equal(t, errors.Is(errItem, btrfstree.ErrNoTree), false)
+	assert.Equal(t, errors.Is(errItem, iofs.ErrNotExist), true)
+
+	// 2
+	assert.Equal(t, errors.Is(errTree, errItem), false)
+	assert.Equal(t, errors.Is(errTree, errTree), true)
+	assert.Equal(t, errors.Is(errTree, btrfstree.ErrNoItem), false)
+	assert.Equal(t, errors.Is(errTree, btrfstree.ErrNoTree), true)
+	assert.Equal(t, errors.Is(errTree, iofs.ErrNotExist), true)
+
+	// 3
+	assert.Equal(t, errors.Is(btrfstree.ErrNoItem, errItem), false)
+	assert.Equal(t, errors.Is(btrfstree.ErrNoItem, errTree), false)
+	assert.Equal(t, errors.Is(btrfstree.ErrNoItem, btrfstree.ErrNoItem), true)
+	assert.Equal(t, errors.Is(btrfstree.ErrNoItem, btrfstree.ErrNoTree), false)
+	assert.Equal(t, errors.Is(btrfstree.ErrNoItem, iofs.ErrNotExist), true)
+
+	// 4
+	assert.Equal(t, errors.Is(btrfstree.ErrNoTree, errItem), false)
+	assert.Equal(t, errors.Is(btrfstree.ErrNoTree, errTree), false)
+	assert.Equal(t, errors.Is(btrfstree.ErrNoTree, btrfstree.ErrNoItem), false)
+	assert.Equal(t, errors.Is(btrfstree.ErrNoTree, btrfstree.ErrNoTree), true)
+	assert.Equal(t, errors.Is(btrfstree.ErrNoTree, iofs.ErrNotExist), true)
+
+	// 5
+	assert.Equal(t, errors.Is(iofs.ErrNotExist, errItem), false)
+	assert.Equal(t, errors.Is(iofs.ErrNotExist, errTree), false)
+	assert.Equal(t, errors.Is(iofs.ErrNotExist, btrfstree.ErrNoItem), false)
+	assert.Equal(t, errors.Is(iofs.ErrNotExist, btrfstree.ErrNoTree), false)
+	assert.Equal(t, errors.Is(iofs.ErrNotExist, iofs.ErrNotExist), true)
+}
diff --git a/lib/btrfs/btrfstree/btree_forrest.go b/lib/btrfs/btrfstree/btree_forrest.go
index 0bab610..625fb30 100644
--- a/lib/btrfs/btrfstree/btree_forrest.go
+++ b/lib/btrfs/btrfstree/btree_forrest.go
@@ -5,6 +5,7 @@
 package btrfstree
 
 import (
+	"errors"
 	"fmt"
 
 	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsitem"
@@ -69,6 +70,9 @@ func LookupTreeRoot(fs TreeOperator, sb Superblock, treeID btrfsprim.ObjID) (*Tr
 	default:
 		rootItem, err := fs.TreeSearch(btrfsprim.ROOT_TREE_OBJECTID, RootItemSearchFn(treeID))
 		if err != nil {
+			if errors.Is(err, ErrNoItem) {
+				err = ErrNoTree
+			}
 			return nil, err
 		}
 		switch rootItemBody := rootItem.Body.(type) {
diff --git a/lib/btrfs/btrfstree/btree_tree.go b/lib/btrfs/btrfstree/btree_tree.go
index afaaf92..c51efa5 100644
--- a/lib/btrfs/btrfstree/btree_tree.go
+++ b/lib/btrfs/btrfstree/btree_tree.go
@@ -180,7 +180,7 @@ func (fs TreeOperatorImpl) treeSearch(treeRoot TreeRoot, fn func(btrfsprim.Key,
 	}}
 	for {
 		if path.Node(-1).ToNodeAddr == 0 {
-			return nil, nil, iofs.ErrNotExist
+			return nil, nil, ErrNoItem
 		}
 		node, err := fs.ReadNode(path)
 		if err != nil {
@@ -204,7 +204,7 @@ func (fs TreeOperatorImpl) treeSearch(treeRoot TreeRoot, fn func(btrfsprim.Key,
 			})
 			if !ok {
 				FreeNodeRef(node)
-				return nil, nil, iofs.ErrNotExist
+				return nil, nil, ErrNoItem
 			}
 			toMaxKey := path.Node(-1).ToMaxKey
 			if lastGood+1 < len(node.Data.BodyInterior) {
@@ -228,7 +228,7 @@ func (fs TreeOperatorImpl) treeSearch(treeRoot TreeRoot, fn func(btrfsprim.Key,
 			//
 			//    + + + + 0 - - - -
 			//
-			// Such an item might not exist; in this case, return nil/ErrNotExist.
+			// Such an item might not exist; in this case, return (nil, ErrNoItem).
 			// Multiple such items might exist; in this case, it does not matter which
 			// is returned.
 			//
@@ -238,7 +238,7 @@ func (fs TreeOperatorImpl) treeSearch(treeRoot TreeRoot, fn func(btrfsprim.Key,
 			})
 			if !ok {
 				FreeNodeRef(node)
-				return nil, nil, iofs.ErrNotExist
+				return nil, nil, ErrNoItem
 			}
 			path = append(path, TreePathElem{
 				FromTree:     node.Data.Head.Owner,