/* * 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 */