auto import from //depot/cupcake/@135843
diff --git a/libc/private/isc/list.h b/libc/private/isc/list.h
new file mode 100644
index 0000000..489766a
--- /dev/null
+++ b/libc/private/isc/list.h
@@ -0,0 +1,114 @@
+/* $NetBSD: list.h,v 1.2 2004/05/20 19:51:55 christos Exp $ */
+
+/*
+ * Copyright (c) 2004 by Internet Systems Consortium, Inc. ("ISC")
+ * Copyright (c) 1997,1999 by Internet Software Consortium.
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
+ * OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#ifndef LIST_H
+#define LIST_H 1
+#include <isc/assertions.h>
+
+#define LIST(type) struct { type *head, *tail; }
+#define INIT_LIST(list) \
+ do { (list).head = NULL; (list).tail = NULL; } while (/*CONSTCOND*/0)
+
+#define LINK(type) struct { type *prev, *next; }
+#define INIT_LINK_TYPE(elt, link, type) \
+ do { \
+ (elt)->link.prev = (type *)(-1); \
+ (elt)->link.next = (type *)(-1); \
+ } while (/*CONSTCOND*/0)
+#define INIT_LINK(elt, link) \
+ INIT_LINK_TYPE(elt, link, void)
+#define LINKED(elt, link) ((void *)((elt)->link.prev) != (void *)(-1))
+
+#define HEAD(list) ((list).head)
+#define TAIL(list) ((list).tail)
+#define EMPTY(list) ((list).head == NULL)
+
+#define PREPEND(list, elt, link) \
+ do { \
+ INSIST(!LINKED(elt, link));\
+ if ((list).head != NULL) \
+ (list).head->link.prev = (elt); \
+ else \
+ (list).tail = (elt); \
+ (elt)->link.prev = NULL; \
+ (elt)->link.next = (list).head; \
+ (list).head = (elt); \
+ } while (/*CONSTCOND*/0)
+
+#define APPEND(list, elt, link) \
+ do { \
+ INSIST(!LINKED(elt, link));\
+ if ((list).tail != NULL) \
+ (list).tail->link.next = (elt); \
+ else \
+ (list).head = (elt); \
+ (elt)->link.prev = (list).tail; \
+ (elt)->link.next = NULL; \
+ (list).tail = (elt); \
+ } while (/*CONSTCOND*/0)
+
+#define UNLINK_TYPE(list, elt, link, type) \
+ do { \
+ INSIST(LINKED(elt, link));\
+ if ((elt)->link.next != NULL) \
+ (elt)->link.next->link.prev = (elt)->link.prev; \
+ else \
+ (list).tail = (elt)->link.prev; \
+ if ((elt)->link.prev != NULL) \
+ (elt)->link.prev->link.next = (elt)->link.next; \
+ else \
+ (list).head = (elt)->link.next; \
+ INIT_LINK_TYPE(elt, link, type); \
+ } while (/*CONSTCOND*/0)
+#define UNLINK(list, elt, link) \
+ UNLINK_TYPE(list, elt, link, void)
+
+#define PREV(elt, link) ((elt)->link.prev)
+#define NEXT(elt, link) ((elt)->link.next)
+
+#define INSERT_BEFORE(list, before, elt, link) \
+ do { \
+ INSIST(!LINKED(elt, link));\
+ if ((before)->link.prev == NULL) \
+ PREPEND(list, elt, link); \
+ else { \
+ (elt)->link.prev = (before)->link.prev; \
+ (before)->link.prev = (elt); \
+ (elt)->link.prev->link.next = (elt); \
+ (elt)->link.next = (before); \
+ } \
+ } while (/*CONSTCOND*/0)
+
+#define INSERT_AFTER(list, after, elt, link) \
+ do { \
+ INSIST(!LINKED(elt, link));\
+ if ((after)->link.next == NULL) \
+ APPEND(list, elt, link); \
+ else { \
+ (elt)->link.next = (after)->link.next; \
+ (after)->link.next = (elt); \
+ (elt)->link.next->link.prev = (elt); \
+ (elt)->link.prev = (after); \
+ } \
+ } while (/*CONSTCOND*/0)
+
+#define ENQUEUE(list, elt, link) APPEND(list, elt, link)
+#define DEQUEUE(list, elt, link) UNLINK(list, elt, link)
+
+#endif /* LIST_H */