1 files changed, 46 insertions, 0 deletions
diff --git a/drivers/md/dm-vdo/indexer/sparse-cache.h b/drivers/md/dm-vdo/indexer/sparse-cache.h
new file mode 100644
index 0000000000..45e2dcf165
--- /dev/null
+++ b/drivers/md/dm-vdo/indexer/sparse-cache.h
@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright 2023 Red Hat
+ */
+
+#ifndef UDS_SPARSE_CACHE_H
+#define UDS_SPARSE_CACHE_H
+
+#include "geometry.h"
+#include "indexer.h"
+
+/*
+ * The sparse cache is a cache of entire chapter indexes from sparse chapters used for searching
+ * for names after all other search paths have failed. It contains only complete chapter indexes;
+ * record pages from sparse chapters and single index pages used for resolving hooks are kept in
+ * the regular page cache in the volume.
+ *
+ * The most important property of this cache is the absence of synchronization for read operations.
+ * Safe concurrent access to the cache by the zone threads is controlled by the triage queue and
+ * the barrier requests it issues to the zone queues. The set of cached chapters does not and must
+ * not change between the carefully coordinated calls to uds_update_sparse_cache() from the zone
+ * threads. Outside of updates, every zone will get the same result when calling
+ * uds_sparse_cache_contains() as every other zone.
+ */
+
+struct index_zone;
+struct sparse_cache;
+
+int __must_check uds_make_sparse_cache(const struct index_geometry *geometry,
+				       unsigned int capacity, unsigned int zone_count,
+				       struct sparse_cache **cache_ptr);
+
+void uds_free_sparse_cache(struct sparse_cache *cache);
+
+bool uds_sparse_cache_contains(struct sparse_cache *cache, u64 virtual_chapter,
+			       unsigned int zone_number);
+
+int __must_check uds_update_sparse_cache(struct index_zone *zone, u64 virtual_chapter);
+
+void uds_invalidate_sparse_cache(struct sparse_cache *cache);
+
+int __must_check uds_search_sparse_cache(struct index_zone *zone,
+					 const struct uds_record_name *name,
+					 u64 *virtual_chapter_ptr, u16 *record_page_ptr);
+
+#endif /* UDS_SPARSE_CACHE_H */