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// 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
}
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