xarray: Add xas_for_each_conflict

This iterator iterates over each entry that is stored in the index or
indices specified by the xa_state.  This is intended for use for a
conditional store of a multiindex entry, or to allow entries which are
about to be removed from the xarray to be disposed of properly.

Signed-off-by: Matthew Wilcox <willy@infradead.org>

1 files changed, 61 insertions, 0 deletions

diff --git a/lib/xarray.c b/lib/xarray.c
index 303c46579598..41f8ebc651f5 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -1111,6 +1111,67 @@ max:
 EXPORT_SYMBOL_GPL(xas_find_marked);
 
 /**
+ * xas_find_conflict() - Find the next present entry in a range.
+ * @xas: XArray operation state.
+ *
+ * The @xas describes both a range and a position within that range.
+ *
+ * Context: Any context.  Expects xa_lock to be held.
+ * Return: The next entry in the range covered by @xas or %NULL.
+ */
+void *xas_find_conflict(struct xa_state *xas)
+{
+        void *curr;
+
+        if (xas_error(xas))
+                return NULL;
+
+        if (!xas->xa_node)
+                return NULL;
+
+        if (xas_top(xas->xa_node)) {
+                curr = xas_start(xas);
+                if (!curr)
+                        return NULL;
+                while (xa_is_node(curr)) {
+                        struct xa_node *node = xa_to_node(curr);
+                        curr = xas_descend(xas, node);
+                }
+                if (curr)
+                        return curr;
+        }
+
+        if (xas->xa_node->shift > xas->xa_shift)
+                return NULL;
+
+        for (;;) {
+                if (xas->xa_node->shift == xas->xa_shift) {
+                        if ((xas->xa_offset & xas->xa_sibs) == xas->xa_sibs)
+                                break;
+                } else if (xas->xa_offset == XA_CHUNK_MASK) {
+                        xas->xa_offset = xas->xa_node->offset;
+                        xas->xa_node = xa_parent_locked(xas->xa, xas->xa_node);
+                        if (!xas->xa_node)
+                                break;
+                        continue;
+                }
+                curr = xa_entry_locked(xas->xa, xas->xa_node, ++xas->xa_offset);
+                if (xa_is_sibling(curr))
+                        continue;
+                while (xa_is_node(curr)) {
+                        xas->xa_node = xa_to_node(curr);
+                        xas->xa_offset = 0;
+                        curr = xa_entry_locked(xas->xa, xas->xa_node, 0);
+                }
+                if (curr)
+                        return curr;
+        }
+        xas->xa_offset -= xas->xa_sibs;
+        return NULL;
+}
+EXPORT_SYMBOL_GPL(xas_find_conflict);
+
+/**
  * xa_init_flags() - Initialise an empty XArray with flags.
  * @xa: XArray.
  * @flags: XA_FLAG values.