list: add macro for iterating through a list an item is in, skipping the item

src/shared/list.h

@@ -138,6 +138,16 @@
 #define LIST_FOREACH_AFTER(name,i,p)                                    \
         for ((i) = (p)->name##_next; (i); (i) = (i)->name##_next)
 
+/* Iterate through all the members of the list p is included in, but skip over p */
+#define LIST_FOREACH_OTHERS(name,i,p)                                   \
+        for (({                                                         \
+                (i) = (p);                                              \
+                while ((i) && (i)->name##_prev)                         \
+                        (i) = (i)->name##_prev;                         \
+             });                                                        \
+             (i);                                                       \
+             (i) = (i)->name##_next == (p) ? (p)->name##_next : (i)->name##_next)
+
 /* Loop starting from p->next until p->prev.
    p can be adjusted meanwhile. */
 #define LIST_LOOP_BUT_ONE(name,i,head,p)                                \

src/test/test-list.c

@@ -38,6 +38,13 @@ int main(int argc, const char *argv[]) {
                 LIST_PREPEND(item, head, &items[i]);
         }
 
+        i = 0;
+        LIST_FOREACH_OTHERS(item, cursor, &items[2]) {
+                i++;
+                assert_se(cursor != &items[2]);
+        }
+        assert_se(i == ELEMENTSOF(items)-1);
+
         assert_se(!LIST_JUST_US(item, head));
 
         assert_se(items[0].item_next == NULL);
@@ -125,7 +132,7 @@ int main(int argc, const char *argv[]) {
         assert_se(items[3].item_prev == &items[2]);
 
         for (i = 0; i < ELEMENTSOF(items); i++)
-          LIST_REMOVE(item, head, &items[i]);
+                LIST_REMOVE(item, head, &items[i]);
 
         assert_se(head == NULL);