list: list_append_list / list_prepend_list

Operations for moving the entire contents of a list.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/ccan/list/list.h b/ccan/list/list.h
index faad86f5c736a3a53ed08c79e74f92c39086a810..8e2f6df0273998764bb89cb69fb4c25d6e5b1070 100644 (file)
--- a/ccan/list/list.h
+++ b/ccan/list/list.h
@@ -371,6 +371,68 @@ static inline const void *list_tail_(const struct list_head *h, size_t off)
 #define list_for_each_safe(h, i, nxt, member)                          \
        list_for_each_safe_off(h, i, nxt, list_off_var_(i, member))
 
+/**
+ * list_append_list - empty one list onto the end of another.
+ * @to: the list to append into
+ * @from: the list to empty.
+ *
+ * This takes the entire contents of @from and moves it to the end of
+ * @to.  After this @from will be empty.
+ *
+ * Example:
+ *     struct list_head adopter;
+ *
+ *     list_append_list(&adopter, &parent->children);
+ *     assert(list_empty(&parent->children));
+ *     parent->num_children = 0;
+ */
+static inline void list_append_list(struct list_head *to,
+                                   struct list_head *from)
+{
+       struct list_node *from_tail = list_debug(from)->n.prev;
+       struct list_node *to_tail = list_debug(to)->n.prev;
+
+       /* Sew in head and entire list. */
+       to->n.prev = from_tail;
+       from_tail->next = &to->n;
+       to_tail->next = &from->n;
+       from->n.prev = to_tail;
+
+       /* Now remove head. */
+       list_del(&from->n);
+       list_head_init(from);
+}
+
+/**
+ * list_prepend_list - empty one list into the start of another.
+ * @to: the list to prepend into
+ * @from: the list to empty.
+ *
+ * This takes the entire contents of @from and moves it to the start
+ * of @to.  After this @from will be empty.
+ *
+ * Example:
+ *     list_prepend_list(&adopter, &parent->children);
+ *     assert(list_empty(&parent->children));
+ *     parent->num_children = 0;
+ */
+static inline void list_prepend_list(struct list_head *to,
+                                    struct list_head *from)
+{
+       struct list_node *from_tail = list_debug(from)->n.prev;
+       struct list_node *to_head = list_debug(to)->n.next;
+
+       /* Sew in head and entire list. */
+       to->n.next = &from->n;
+       from->n.prev = &to->n;
+       to_head->prev = from_tail;
+       from_tail->next = to_head;
+
+       /* Now remove head. */
+       list_del(&from->n);
+       list_head_init(from);
+}
+
 /**
  * list_for_each_off - iterate through a list of memory regions.
  * @h: the list_head

diff --git a/ccan/list/test/run-prepend_list.c b/ccan/list/test/run-prepend_list.c
new file mode 100644 (file)
index 0000000..d382f5a
--- /dev/null
+++ b/ccan/list/test/run-prepend_list.c
@@ -0,0 +1,111 @@
+#include <ccan/list/list.h>
+#include <ccan/tap/tap.h>
+#include <ccan/list/list.c>
+#include <stdarg.h>
+
+static bool list_expect(struct list_head *h, ...)
+{
+       va_list ap;
+       struct list_node *n = &h->n, *expected;
+
+       va_start(ap, h);
+       while ((expected = va_arg(ap, struct list_node *)) != NULL) {
+               n = n->next;
+               if (n != expected)
+                       return false;
+       }
+       return (n->next == &h->n);
+}
+
+int main(int argc, char *argv[])
+{
+       struct list_head h1, h2;
+       struct list_node n[4];
+
+       plan_tests(40);
+
+       list_head_init(&h1);
+       list_head_init(&h2);
+
+       /* Append an empty list to an empty list. */
+       list_append_list(&h1, &h2);
+       ok1(list_empty(&h1));
+       ok1(list_empty(&h2));
+       ok1(list_check(&h1, NULL));
+       ok1(list_check(&h2, NULL));
+
+       /* Prepend an empty list to an empty list. */
+       list_prepend_list(&h1, &h2);
+       ok1(list_empty(&h1));
+       ok1(list_empty(&h2));
+       ok1(list_check(&h1, NULL));
+       ok1(list_check(&h2, NULL));
+
+       /* Append an empty list to a non-empty list */
+       list_add(&h1, &n[0]);
+       list_append_list(&h1, &h2);
+       ok1(list_empty(&h2));
+       ok1(list_check(&h1, NULL));
+       ok1(list_check(&h2, NULL));
+       ok1(list_expect(&h1, &n[0], NULL));
+
+       /* Prepend an empty list to a non-empty list */
+       list_prepend_list(&h1, &h2);
+       ok1(list_empty(&h2));
+       ok1(list_check(&h1, NULL));
+       ok1(list_check(&h2, NULL));
+       ok1(list_expect(&h1, &n[0], NULL));
+
+       /* Append a non-empty list to an empty list. */
+       list_append_list(&h2, &h1);
+       ok1(list_empty(&h1));
+       ok1(list_check(&h1, NULL));
+       ok1(list_check(&h2, NULL));
+       ok1(list_expect(&h2, &n[0], NULL));
+
+       /* Prepend a non-empty list to an empty list. */
+       list_prepend_list(&h1, &h2);
+       ok1(list_empty(&h2));
+       ok1(list_check(&h1, NULL));
+       ok1(list_check(&h2, NULL));
+       ok1(list_expect(&h1, &n[0], NULL));
+
+       /* Prepend a non-empty list to non-empty list. */
+       list_add(&h2, &n[1]);
+       list_prepend_list(&h1, &h2);
+       ok1(list_empty(&h2));
+       ok1(list_check(&h1, NULL));
+       ok1(list_check(&h2, NULL));
+       ok1(list_expect(&h1, &n[1], &n[0], NULL));
+
+       /* Append a non-empty list to non-empty list. */
+       list_add(&h2, &n[2]);
+       list_append_list(&h1, &h2);
+       ok1(list_empty(&h2));
+       ok1(list_check(&h1, NULL));
+       ok1(list_check(&h2, NULL));
+       ok1(list_expect(&h1, &n[1], &n[0], &n[2], NULL));
+
+       /* Prepend a 2-entry list to a 2-entry list. */
+       list_del_from(&h1, &n[2]);
+       list_add(&h2, &n[2]);
+       list_add_tail(&h2, &n[3]);
+       list_prepend_list(&h1, &h2);
+       ok1(list_empty(&h2));
+       ok1(list_check(&h1, NULL));
+       ok1(list_check(&h2, NULL));
+       ok1(list_expect(&h1, &n[2], &n[3], &n[1], &n[0], NULL));
+
+       /* Append a 2-entry list to a 2-entry list. */
+       list_del_from(&h1, &n[2]);
+       list_del_from(&h1, &n[3]);
+       list_add(&h2, &n[2]);
+       list_add_tail(&h2, &n[3]);
+       list_append_list(&h1, &h2);
+       ok1(list_empty(&h2));
+       ok1(list_check(&h1, NULL));
+       ok1(list_check(&h2, NULL));
+       ok1(list_expect(&h1, &n[1], &n[0], &n[2], &n[3], NULL));
+
+       return exit_status();
+}