1 files changed, 186 insertions, 0 deletions
diff --git a/drivers/md/dm-cache-policy.h b/drivers/md/dm-cache-policy.h
new file mode 100644
index 000000000..c05fc3436
--- /dev/null
+++ b/drivers/md/dm-cache-policy.h
@@ -0,0 +1,186 @@
+/*
+ * Copyright (C) 2012 Red Hat. All rights reserved.
+ *
+ * This file is released under the GPL.
+ */
+
+#ifndef DM_CACHE_POLICY_H
+#define DM_CACHE_POLICY_H
+
+#include "dm-cache-block-types.h"
+
+#include <linux/device-mapper.h>
+
+/*----------------------------------------------------------------*/
+
+/*
+ * The cache policy makes the important decisions about which blocks get to
+ * live on the faster cache device.
+ */
+enum policy_operation {
+	POLICY_PROMOTE,
+	POLICY_DEMOTE,
+	POLICY_WRITEBACK
+};
+
+/*
+ * This is the instruction passed back to the core target.
+ */
+struct policy_work {
+	enum policy_operation op;
+	dm_oblock_t oblock;
+	dm_cblock_t cblock;
+};
+
+/*
+ * The cache policy object.  It is envisaged that this structure will be
+ * embedded in a bigger, policy specific structure (ie. use container_of()).
+ */
+struct dm_cache_policy {
+	/*
+	 * Destroys this object.
+	 */
+	void (*destroy)(struct dm_cache_policy *p);
+
+	/*
+	 * Find the location of a block.
+	 *
+	 * Must not block.
+	 *
+	 * Returns 0 if in cache (cblock will be set), -ENOENT if not, < 0 for
+	 * other errors (-EWOULDBLOCK would be typical).  data_dir should be
+	 * READ or WRITE. fast_copy should be set if migrating this block would
+	 * be 'cheap' somehow (eg, discarded data). background_queued will be set
+	 * if a migration has just been queued.
+	 */
+	int (*lookup)(struct dm_cache_policy *p, dm_oblock_t oblock, dm_cblock_t *cblock,
+		      int data_dir, bool fast_copy, bool *background_queued);
+
+	/*
+	 * Sometimes the core target can optimise a migration, eg, the
+	 * block may be discarded, or the bio may cover an entire block.
+	 * In order to optimise it needs the migration immediately though
+	 * so it knows to do something different with the bio.
+	 *
+	 * This method is optional (policy-internal will fallback to using
+	 * lookup).
+	 */
+	int (*lookup_with_work)(struct dm_cache_policy *p,
+				dm_oblock_t oblock, dm_cblock_t *cblock,
+				int data_dir, bool fast_copy,
+				struct policy_work **work);
+
+	/*
+	 * Retrieves background work.  Returns -ENODATA when there's no
+	 * background work.
+	 */
+	int (*get_background_work)(struct dm_cache_policy *p, bool idle,
+			           struct policy_work **result);
+
+	/*
+	 * You must pass in the same work pointer that you were given, not
+	 * a copy.
+	 */
+	void (*complete_background_work)(struct dm_cache_policy *p,
+					 struct policy_work *work,
+					 bool success);
+
+	void (*set_dirty)(struct dm_cache_policy *p, dm_cblock_t cblock);
+	void (*clear_dirty)(struct dm_cache_policy *p, dm_cblock_t cblock);
+
+	/*
+	 * Called when a cache target is first created.  Used to load a
+	 * mapping from the metadata device into the policy.
+	 */
+	int (*load_mapping)(struct dm_cache_policy *p, dm_oblock_t oblock,
+			    dm_cblock_t cblock, bool dirty,
+			    uint32_t hint, bool hint_valid);
+
+	/*
+	 * Drops the mapping, irrespective of whether it's clean or dirty.
+	 * Returns -ENODATA if cblock is not mapped.
+	 */
+	int (*invalidate_mapping)(struct dm_cache_policy *p, dm_cblock_t cblock);
+
+	/*
+	 * Gets the hint for a given cblock.  Called in a single threaded
+	 * context.  So no locking required.
+	 */
+	uint32_t (*get_hint)(struct dm_cache_policy *p, dm_cblock_t cblock);
+
+	/*
+	 * How full is the cache?
+	 */
+	dm_cblock_t (*residency)(struct dm_cache_policy *p);
+
+	/*
+	 * Because of where we sit in the block layer, we can be asked to
+	 * map a lot of little bios that are all in the same block (no
+	 * queue merging has occurred).  To stop the policy being fooled by
+	 * these, the core target sends regular tick() calls to the policy.
+	 * The policy should only count an entry as hit once per tick.
+	 *
+	 * This method is optional.
+	 */
+	void (*tick)(struct dm_cache_policy *p, bool can_block);
+
+	/*
+	 * Configuration.
+	 */
+	int (*emit_config_values)(struct dm_cache_policy *p, char *result,
+				  unsigned maxlen, ssize_t *sz_ptr);
+	int (*set_config_value)(struct dm_cache_policy *p,
+				const char *key, const char *value);
+
+	void (*allow_migrations)(struct dm_cache_policy *p, bool allow);
+
+	/*
+	 * Book keeping ptr for the policy register, not for general use.
+	 */
+	void *private;
+};
+
+/*----------------------------------------------------------------*/
+
+/*
+ * We maintain a little register of the different policy types.
+ */
+#define CACHE_POLICY_NAME_SIZE 16
+#define CACHE_POLICY_VERSION_SIZE 3
+
+struct dm_cache_policy_type {
+	/* For use by the register code only. */
+	struct list_head list;
+
+	/*
+	 * Policy writers should fill in these fields.  The name field is
+	 * what gets passed on the target line to select your policy.
+	 */
+	char name[CACHE_POLICY_NAME_SIZE];
+	unsigned version[CACHE_POLICY_VERSION_SIZE];
+
+	/*
+	 * For use by an alias dm_cache_policy_type to point to the
+	 * real dm_cache_policy_type.
+	 */
+	struct dm_cache_policy_type *real;
+
+	/*
+	 * Policies may store a hint for each each cache block.
+	 * Currently the size of this hint must be 0 or 4 bytes but we
+	 * expect to relax this in future.
+	 */
+	size_t hint_size;
+
+	struct module *owner;
+	struct dm_cache_policy *(*create)(dm_cblock_t cache_size,
+					  sector_t origin_size,
+					  sector_t block_size);
+};
+
+int dm_cache_policy_register(struct dm_cache_policy_type *type);
+void dm_cache_policy_unregister(struct dm_cache_policy_type *type);
+
+/*----------------------------------------------------------------*/
+
+#endif	/* DM_CACHE_POLICY_H */