list: list_swap to exchange elements

This allows deleting and re-inserting an element in place
of the deleted element without branching.

Signed-off-by: Eric Wong <normalperson@yhbt.net>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/ccan/list/list.h b/ccan/list/list.h
index 5c1159f48159987994341266616620f6f1c915c1..983675b81f9d53877fd5d0dfaa56abc1d742a641 100644 (file)
--- a/ccan/list/list.h
+++ b/ccan/list/list.h
@@ -368,6 +368,39 @@ static inline void list_del_from(struct list_head *h, struct list_node *n)
        list_del(n);
 }
 
        list_del(n);
 }
 

+/**
+ * list_swap - swap out an entry from an (unknown) linked list for a new one.
+ * @o: the list_node to replace from the list.
+ * @n: the list_node to insert in place of the old one.
+ *
+ * Note that this leaves @o in an undefined state; it can be added to
+ * another list, but not deleted/swapped again.
+ *
+ * See also:
+ *     list_del()
+ *
+ * Example:
+ *     struct child x1, x2;
+ *     LIST_HEAD(xh);
+ *
+ *     list_add(&xh, &x1.list);
+ *     list_swap(&x1.list, &x2.list);
+ */
+#define list_swap(o, n) list_swap_(o, n, LIST_LOC)
+static inline void list_swap_(struct list_node *o,
+                             struct list_node *n,
+                             const char* abortstr)
+{
+       (void)list_debug_node(o, abortstr);
+       *n = *o;
+       n->next->prev = n;
+       n->prev->next = n;
+#ifdef CCAN_LIST_DEBUG
+       /* Catch use-after-del. */
+       o->next = o->prev = NULL;
+#endif
+}
+

 /**
  * list_entry - convert a list_node back into the structure containing it.
  * @n: the list_node
 /**
  * list_entry - convert a list_node back into the structure containing it.
  * @n: the list_node

diff --git a/ccan/list/test/run.c b/ccan/list/test/run.c
index 2f1acc78a0605e959fbc94a21cd7eae2a5595018..306744598e2461a5bd6eb28de70593c7b009088e 100644 (file)
--- a/ccan/list/test/run.c
+++ b/ccan/list/test/run.c
@@ -19,13 +19,13 @@ static LIST_HEAD(static_list);
 int main(int argc, char *argv[])
 {
        struct parent parent;
 int main(int argc, char *argv[])
 {
        struct parent parent;

-       struct child c1, c2, c3, *c, *n;
+       struct child c1, c2, c3, x1, *c, *n;

        unsigned int i;
        struct list_head list = LIST_HEAD_INIT(list);
        opaque_t *q, *nq;
        struct list_head opaque_list = LIST_HEAD_INIT(opaque_list);
 
        unsigned int i;
        struct list_head list = LIST_HEAD_INIT(list);
        opaque_t *q, *nq;
        struct list_head opaque_list = LIST_HEAD_INIT(opaque_list);
 

-       plan_tests(79);
+       plan_tests(84);

        /* Test LIST_HEAD, LIST_HEAD_INIT, list_empty and check_list */
        ok1(list_empty(&static_list));
        ok1(list_check(&static_list, NULL));
        /* Test LIST_HEAD, LIST_HEAD_INIT, list_empty and check_list */
        ok1(list_empty(&static_list));
        ok1(list_check(&static_list, NULL));


@@ -253,5 +253,24 @@ int main(int argc, char *argv[])
        }
        ok1(i == 3);
 
        }
        ok1(i == 3);
 

+       /* test list_swap */
+       list_swap(&c3.list, &x1.list);
+       ok1(list_check(&parent.children, "list_swap"));
+       i = 0;
+       list_for_each(&parent.children, c, list) {
+               switch (i++) {
+               case 0:
+                       ok1(c == &c1);
+                       break;
+               case 1:
+                       ok1(c == &x1);
+                       break;
+               case 2:
+                       ok1(c == &c2);
+                       break;
+               }
+       }
+       ok1(i == 3);
+

        return exit_status();
 }
        return exit_status();
 }