dm array: introduce cursor api

More efficient way to iterate an array due to prefetching (makes use of
the new dm_btree_cursor_* api).

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

2 files changed, 119 insertions, 0 deletions

diff --git a/drivers/md/persistent-data/dm-array.c b/drivers/md/persistent-data/dm-array.c
index 155180954cdf..e83047cbb2da 100644
--- a/drivers/md/persistent-data/dm-array.c
+++ b/drivers/md/persistent-data/dm-array.c
@@ -899,3 +899,89 @@ int dm_array_walk(struct dm_array_info *info, dm_block_t root,
 EXPORT_SYMBOL_GPL(dm_array_walk);
 
 /*----------------------------------------------------------------*/
+
+static int load_ablock(struct dm_array_cursor *c)
+{
+        int r;
+        __le64 value_le;
+        uint64_t key;
+
+        if (c->block)
+                unlock_ablock(c->info, c->block);
+
+        c->block = NULL;
+        c->ab = NULL;
+        c->index = 0;
+
+        r = dm_btree_cursor_get_value(&c->cursor, &key, &value_le);
+        if (r) {
+                DMERR("dm_btree_cursor_get_value failed");
+                dm_btree_cursor_end(&c->cursor);
+
+        } else {
+                r = get_ablock(c->info, le64_to_cpu(value_le), &c->block, &c->ab);
+                if (r) {
+                        DMERR("get_ablock failed");
+                        dm_btree_cursor_end(&c->cursor);
+                }
+        }
+
+        return r;
+}
+
+int dm_array_cursor_begin(struct dm_array_info *info, dm_block_t root,
+                          struct dm_array_cursor *c)
+{
+        int r;
+
+        memset(c, 0, sizeof(*c));
+        c->info = info;
+        r = dm_btree_cursor_begin(&info->btree_info, root, true, &c->cursor);
+        if (r) {
+                DMERR("couldn't create btree cursor");
+                return r;
+        }
+
+        return load_ablock(c);
+}
+EXPORT_SYMBOL_GPL(dm_array_cursor_begin);
+
+void dm_array_cursor_end(struct dm_array_cursor *c)
+{
+        if (c->block) {
+                unlock_ablock(c->info, c->block);
+                dm_btree_cursor_end(&c->cursor);
+        }
+}
+EXPORT_SYMBOL_GPL(dm_array_cursor_end);
+
+int dm_array_cursor_next(struct dm_array_cursor *c)
+{
+        int r;
+
+        if (!c->block)
+                return -ENODATA;
+
+        c->index++;
+
+        if (c->index >= le32_to_cpu(c->ab->nr_entries)) {
+                r = dm_btree_cursor_next(&c->cursor);
+                if (r)
+                        return r;
+
+                r = load_ablock(c);
+                if (r)
+                        return r;
+        }
+
+        return 0;
+}
+EXPORT_SYMBOL_GPL(dm_array_cursor_next);
+
+void dm_array_cursor_get_value(struct dm_array_cursor *c, void **value_le)
+{
+        *value_le = element_at(c->info, c->ab, c->index);
+}
+EXPORT_SYMBOL_GPL(dm_array_cursor_get_value);
+
+/*----------------------------------------------------------------*/
diff --git a/drivers/md/persistent-data/dm-array.h b/drivers/md/persistent-data/dm-array.h
index 45ea3f6e1ded..27ee49a55473 100644
--- a/drivers/md/persistent-data/dm-array.h
+++ b/drivers/md/persistent-data/dm-array.h
@@ -182,4 +182,37 @@ int dm_array_walk(struct dm_array_info *info, dm_block_t root,
 
 /*----------------------------------------------------------------*/
 
+/*
+ * Cursor api.
+ *
+ * This lets you iterate through all the entries in an array efficiently
+ * (it will preload metadata).
+ *
+ * I'm using a cursor, rather than a walk function with a callback because
+ * the cache target needs to iterate both the mapping and hint arrays in
+ * unison.
+ */
+struct dm_array_cursor {
+        struct dm_array_info *info;
+        struct dm_btree_cursor cursor;
+
+        struct dm_block *block;
+        struct array_block *ab;
+        unsigned index;
+};
+
+int dm_array_cursor_begin(struct dm_array_info *info,
+                          dm_block_t root, struct dm_array_cursor *c);
+void dm_array_cursor_end(struct dm_array_cursor *c);
+
+uint32_t dm_array_cursor_index(struct dm_array_cursor *c);
+int dm_array_cursor_next(struct dm_array_cursor *c);
+
+/*
+ * value_le is only valid while the cursor points at the current value.
+ */
+void dm_array_cursor_get_value(struct dm_array_cursor *c, void **value_le);
+
+/*----------------------------------------------------------------*/
+
 #endif  /* _LINUX_DM_ARRAY_H */