Initial commit

Proof-of-concept implementation. Bugs will occur.

vendor/github.com/hanwen/go-fuse/v2/fs/inode_parents.go

@@ -0,0 +1,101 @@
+// Copyright 2021 the Go-FUSE Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package fs
+
+// inodeParents stores zero or more parents of an Inode,
+// remembering which one is the most recent.
+//
+// No internal locking: the caller is responsible for preventing
+// concurrent access.
+type inodeParents struct {
+	// newest is the most-recently add()'ed parent.
+	// nil when we don't have any parents.
+	newest *parentData
+	// other are parents in addition to the newest.
+	// nil or empty when we have <= 1 parents.
+	other map[parentData]struct{}
+}
+
+// add adds a parent to the store.
+func (p *inodeParents) add(n parentData) {
+	// one and only parent
+	if p.newest == nil {
+		p.newest = &n
+	}
+	// already known as `newest`
+	if *p.newest == n {
+		return
+	}
+	// old `newest` gets displaced into `other`
+	if p.other == nil {
+		p.other = make(map[parentData]struct{})
+	}
+	p.other[*p.newest] = struct{}{}
+	// new parent becomes `newest` (possibly moving up from `other`)
+	delete(p.other, n)
+	p.newest = &n
+}
+
+// get returns the most recent parent
+// or nil if there is no parent at all.
+func (p *inodeParents) get() *parentData {
+	return p.newest
+}
+
+// all returns all known parents
+// or nil if there is no parent at all.
+func (p *inodeParents) all() []parentData {
+	count := p.count()
+	if count == 0 {
+		return nil
+	}
+	out := make([]parentData, 0, count)
+	out = append(out, *p.newest)
+	for i := range p.other {
+		out = append(out, i)
+	}
+	return out
+}
+
+func (p *inodeParents) delete(n parentData) {
+	// We have zero parents, so we can't delete any.
+	if p.newest == nil {
+		return
+	}
+	// If it's not the `newest` it must be in `other` (or nowhere).
+	if *p.newest != n {
+		delete(p.other, n)
+		return
+	}
+	// We want to delete `newest`, but there is no other to replace it.
+	if len(p.other) == 0 {
+		p.newest = nil
+		return
+	}
+	// Move random entry from `other` over `newest`.
+	var i parentData
+	for i = range p.other {
+		p.newest = &i
+		break
+	}
+	delete(p.other, i)
+}
+
+func (p *inodeParents) clear() {
+	p.newest = nil
+	p.other = nil
+}
+
+func (p *inodeParents) count() int {
+	if p.newest == nil {
+		return 0
+	}
+	return 1 + len(p.other)
+}
+
+type parentData struct {
+	name   string
+	parent *Inode
+}