dm: add cache target

Add a target that allows a fast device such as an SSD to be used as a
cache for a slower device such as a disk.

A plug-in architecture was chosen so that the decisions about which data
to migrate and when are delegated to interchangeable tunable policy
modules.  The first general purpose module we have developed, called
"mq" (multiqueue), follows in the next patch.  Other modules are
under development.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Heinz Mauelshagen <mauelshagen@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 124 insertions, 0 deletions

diff --git a/drivers/md/dm-cache-policy-internal.h b/drivers/md/dm-cache-policy-internal.h
new file mode 100644
index 000000000000..52a75beeced5
--- /dev/null
+++ b/drivers/md/dm-cache-policy-internal.h
@@ -0,0 +1,124 @@
+/*
+ * Copyright (C) 2012 Red Hat. All rights reserved.
+ *
+ * This file is released under the GPL.
+ */
+
+#ifndef DM_CACHE_POLICY_INTERNAL_H
+#define DM_CACHE_POLICY_INTERNAL_H
+
+#include "dm-cache-policy.h"
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Little inline functions that simplify calling the policy methods.
+ */
+static inline int policy_map(struct dm_cache_policy *p, dm_oblock_t oblock,
+			     bool can_block, bool can_migrate, bool discarded_oblock,
+			     struct bio *bio, struct policy_result *result)
+{
+	return p->map(p, oblock, can_block, can_migrate, discarded_oblock, bio, result);
+}
+
+static inline int policy_lookup(struct dm_cache_policy *p, dm_oblock_t oblock, dm_cblock_t *cblock)
+{
+	BUG_ON(!p->lookup);
+	return p->lookup(p, oblock, cblock);
+}
+
+static inline void policy_set_dirty(struct dm_cache_policy *p, dm_oblock_t oblock)
+{
+	if (p->set_dirty)
+		p->set_dirty(p, oblock);
+}
+
+static inline void policy_clear_dirty(struct dm_cache_policy *p, dm_oblock_t oblock)
+{
+	if (p->clear_dirty)
+		p->clear_dirty(p, oblock);
+}
+
+static inline int policy_load_mapping(struct dm_cache_policy *p,
+				      dm_oblock_t oblock, dm_cblock_t cblock,
+				      uint32_t hint, bool hint_valid)
+{
+	return p->load_mapping(p, oblock, cblock, hint, hint_valid);
+}
+
+static inline int policy_walk_mappings(struct dm_cache_policy *p,
+				      policy_walk_fn fn, void *context)
+{
+	return p->walk_mappings ? p->walk_mappings(p, fn, context) : 0;
+}
+
+static inline int policy_writeback_work(struct dm_cache_policy *p,
+					dm_oblock_t *oblock,
+					dm_cblock_t *cblock)
+{
+	return p->writeback_work ? p->writeback_work(p, oblock, cblock) : -ENOENT;
+}
+
+static inline void policy_remove_mapping(struct dm_cache_policy *p, dm_oblock_t oblock)
+{
+	return p->remove_mapping(p, oblock);
+}
+
+static inline void policy_force_mapping(struct dm_cache_policy *p,
+					dm_oblock_t current_oblock, dm_oblock_t new_oblock)
+{
+	return p->force_mapping(p, current_oblock, new_oblock);
+}
+
+static inline dm_cblock_t policy_residency(struct dm_cache_policy *p)
+{
+	return p->residency(p);
+}
+
+static inline void policy_tick(struct dm_cache_policy *p)
+{
+	if (p->tick)
+		return p->tick(p);
+}
+
+static inline int policy_emit_config_values(struct dm_cache_policy *p, char *result, unsigned maxlen)
+{
+	ssize_t sz = 0;
+	if (p->emit_config_values)
+		return p->emit_config_values(p, result, maxlen);
+
+	DMEMIT("0");
+	return 0;
+}
+
+static inline int policy_set_config_value(struct dm_cache_policy *p,
+					  const char *key, const char *value)
+{
+	return p->set_config_value ? p->set_config_value(p, key, value) : -EINVAL;
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Creates a new cache policy given a policy name, a cache size, an origin size and the block size.
+ */
+struct dm_cache_policy *dm_cache_policy_create(const char *name, dm_cblock_t cache_size,
+					       sector_t origin_size, sector_t block_size);
+
+/*
+ * Destroys the policy.  This drops references to the policy module as well
+ * as calling it's destroy method.  So always use this rather than calling
+ * the policy->destroy method directly.
+ */
+void dm_cache_policy_destroy(struct dm_cache_policy *p);
+
+/*
+ * In case we've forgotten.
+ */
+const char *dm_cache_policy_get_name(struct dm_cache_policy *p);
+
+size_t dm_cache_policy_get_hint_size(struct dm_cache_policy *p);
+
+/*----------------------------------------------------------------*/
+
+#endif /* DM_CACHE_POLICY_INTERNAL_H */