1 files changed, 171 insertions, 0 deletions
diff --git a/pkg/ilist/list.go b/pkg/ilist/list.go
new file mode 100644
index 000000000..739575f17
--- /dev/null
+++ b/pkg/ilist/list.go
@@ -0,0 +1,171 @@
+// Copyright 2016 The Netstack 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 ilist provides the implementation of intrusive linked lists.
+package ilist
+
+// Linker is the interface that objects must implement if they want to be added
+// to and/or removed from List objects.
+//
+// N.B. When substituted in a template instantiation, Linker doesn't need to
+// be an interface, and in most cases won't be.
+type Linker interface {
+	Next() Linker
+	Prev() Linker
+	SetNext(Linker)
+	SetPrev(Linker)
+}
+
+// List is an intrusive list. Entries can be added to or removed from the list
+// in O(1) time and with no additional memory allocations.
+//
+// The zero value for List is an empty list ready to use.
+//
+// To iterate over a list (where l is a List):
+//      for e := l.Front(); e != nil; e = e.Next() {
+// 		// do something with e.
+//      }
+type List struct {
+	head Linker
+	tail Linker
+}
+
+// Reset resets list l to the empty state.
+func (l *List) Reset() {
+	l.head = nil
+	l.tail = nil
+}
+
+// Empty returns true iff the list is empty.
+func (l *List) Empty() bool {
+	return l.head == nil
+}
+
+// Front returns the first element of list l or nil.
+func (l *List) Front() Linker {
+	return l.head
+}
+
+// Back returns the last element of list l or nil.
+func (l *List) Back() Linker {
+	return l.tail
+}
+
+// PushFront inserts the element e at the front of list l.
+func (l *List) PushFront(e Linker) {
+	e.SetNext(l.head)
+	e.SetPrev(nil)
+
+	if l.head != nil {
+		l.head.SetPrev(e)
+	} else {
+		l.tail = e
+	}
+
+	l.head = e
+}
+
+// PushBack inserts the element e at the back of list l.
+func (l *List) PushBack(e Linker) {
+	e.SetNext(nil)
+	e.SetPrev(l.tail)
+
+	if l.tail != nil {
+		l.tail.SetNext(e)
+	} else {
+		l.head = e
+	}
+
+	l.tail = e
+}
+
+// PushBackList inserts list m at the end of list l, emptying m.
+func (l *List) PushBackList(m *List) {
+	if l.head == nil {
+		l.head = m.head
+		l.tail = m.tail
+	} else if m.head != nil {
+		l.tail.SetNext(m.head)
+		m.head.SetPrev(l.tail)
+
+		l.tail = m.tail
+	}
+
+	m.head = nil
+	m.tail = nil
+}
+
+// InsertAfter inserts e after b.
+func (l *List) InsertAfter(b, e Linker) {
+	a := b.Next()
+	e.SetNext(a)
+	e.SetPrev(b)
+	b.SetNext(e)
+
+	if a != nil {
+		a.SetPrev(e)
+	} else {
+		l.tail = e
+	}
+}
+
+// InsertBefore inserts e before a.
+func (l *List) InsertBefore(a, e Linker) {
+	b := a.Prev()
+	e.SetNext(a)
+	e.SetPrev(b)
+	a.SetPrev(e)
+
+	if b != nil {
+		b.SetNext(e)
+	} else {
+		l.head = e
+	}
+}
+
+// Remove removes e from l.
+func (l *List) Remove(e Linker) {
+	prev := e.Prev()
+	next := e.Next()
+
+	if prev != nil {
+		prev.SetNext(next)
+	} else {
+		l.head = next
+	}
+
+	if next != nil {
+		next.SetPrev(prev)
+	} else {
+		l.tail = prev
+	}
+}
+
+// Entry is a default implementation of Linker. Users can add anonymous fields
+// of this type to their structs to make them automatically implement the
+// methods needed by List.
+type Entry struct {
+	next Linker
+	prev Linker
+}
+
+// Next returns the entry that follows e in the list.
+func (e *Entry) Next() Linker {
+	return e.next
+}
+
+// Prev returns the entry that precedes e in the list.
+func (e *Entry) Prev() Linker {
+	return e.prev
+}
+
+// SetNext assigns 'entry' as the entry that follows e in the list.
+func (e *Entry) SetNext(entry Linker) {
+	e.next = entry
+}
+
+// SetPrev assigns 'entry' as the entry that precedes e in the list.
+func (e *Entry) SetPrev(entry Linker) {
+	e.prev = entry
+}