list_bl: Add hlist_bl_add_before/behind helpers

Add hlist_bl_add_before/behind helpers to add an element before/after an
existing element in a bl_list.

Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Reviewed-by: Paul E. McKenney <paulmck@linux.ibm.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/include/linux/list_bl.h b/include/linux/list_bl.h
index 3fc2cc57ba1bc6d5badfd24ef67982683457507e..ae1b541446c906158cb057538b62241161e4b361 100644 (file)
--- a/include/linux/list_bl.h
+++ b/include/linux/list_bl.h
@@ -86,6 +86,32 @@ static inline void hlist_bl_add_head(struct hlist_bl_node *n,
        hlist_bl_set_first(h, n);
 }
 
+static inline void hlist_bl_add_before(struct hlist_bl_node *n,
+                                      struct hlist_bl_node *next)
+{
+       struct hlist_bl_node **pprev = next->pprev;
+
+       n->pprev = pprev;
+       n->next = next;
+       next->pprev = &n->next;
+
+       /* pprev may be `first`, so be careful not to lose the lock bit */
+       WRITE_ONCE(*pprev,
+                  (struct hlist_bl_node *)
+                       ((uintptr_t)n | ((uintptr_t)*pprev & LIST_BL_LOCKMASK)));
+}
+
+static inline void hlist_bl_add_behind(struct hlist_bl_node *n,
+                                      struct hlist_bl_node *prev)
+{
+       n->next = prev->next;
+       n->pprev = &prev->next;
+       prev->next = n;
+
+       if (n->next)
+               n->next->pprev = &n->next;
+}
+
 static inline void __hlist_bl_del(struct hlist_bl_node *n)
 {
        struct hlist_bl_node *next = n->next;