From 2e0c76aee25f33c482abda6224bd87732359354d Mon Sep 17 00:00:00 2001 From: David Howells Date: Wed, 20 Oct 2021 15:00:26 +0100 Subject: [PATCH] fscache: Implement functions add/remove a cache Implement functions to allow the cache backend to add or remove a cache: (1) Declare a cache to be live: int fscache_add_cache(struct fscache_cache *cache, const struct fscache_cache_ops *ops, void *cache_priv); Take a previously acquired cache cookie, set the operations table and private data and mark the cache open for access. (2) Withdraw a cache from service: void fscache_withdraw_cache(struct fscache_cache *cache); This marks the cache as withdrawn and thus prevents further cache-level and volume-level accesses. Signed-off-by: David Howells Reviewed-by: Jeff Layton cc: linux-cachefs@redhat.com Link: https://lore.kernel.org/r/163819596022.215744.8799712491432238827.stgit@warthog.procyon.org.uk/ # v1 Link: https://lore.kernel.org/r/163906896599.143852.17049208999019262884.stgit@warthog.procyon.org.uk/ # v2 Link: https://lore.kernel.org/r/163967097870.1823006.3470041000971522030.stgit@warthog.procyon.org.uk/ # v3 Link: https://lore.kernel.org/r/164021505541.640689.1819714759326331054.stgit@warthog.procyon.org.uk/ # v4 --- fs/fscache/cache.c | 70 +++++++++++++++++++++++++++++++++++ include/linux/fscache-cache.h | 13 +++++++ 2 files changed, 83 insertions(+) diff --git a/fs/fscache/cache.c b/fs/fscache/cache.c index e867cff53a70..bbd102be91c4 100644 --- a/fs/fscache/cache.c +++ b/fs/fscache/cache.c @@ -210,12 +210,55 @@ void fscache_relinquish_cache(struct fscache_cache *cache) fscache_cache_put_prep_failed : fscache_cache_put_relinquish; + cache->ops = NULL; cache->cache_priv = NULL; smp_store_release(&cache->state, FSCACHE_CACHE_IS_NOT_PRESENT); fscache_put_cache(cache, where); } EXPORT_SYMBOL(fscache_relinquish_cache); +/** + * fscache_add_cache - Declare a cache as being open for business + * @cache: The cache-level cookie representing the cache + * @ops: Table of cache operations to use + * @cache_priv: Private data for the cache record + * + * Add a cache to the system, making it available for netfs's to use. + * + * See Documentation/filesystems/caching/backend-api.rst for a complete + * description. + */ +int fscache_add_cache(struct fscache_cache *cache, + const struct fscache_cache_ops *ops, + void *cache_priv) +{ + int n_accesses; + + _enter("{%s,%s}", ops->name, cache->name); + + BUG_ON(fscache_cache_state(cache) != FSCACHE_CACHE_IS_PREPARING); + + /* Get a ref on the cache cookie and keep its n_accesses counter raised + * by 1 to prevent wakeups from transitioning it to 0 until we're + * withdrawing caching services from it. + */ + n_accesses = atomic_inc_return(&cache->n_accesses); + trace_fscache_access_cache(cache->debug_id, refcount_read(&cache->ref), + n_accesses, fscache_access_cache_pin); + + down_write(&fscache_addremove_sem); + + cache->ops = ops; + cache->cache_priv = cache_priv; + fscache_set_cache_state(cache, FSCACHE_CACHE_IS_ACTIVE); + + up_write(&fscache_addremove_sem); + pr_notice("Cache \"%s\" added (type %s)\n", cache->name, ops->name); + _leave(" = 0 [%s]", cache->name); + return 0; +} +EXPORT_SYMBOL(fscache_add_cache); + /** * fscache_begin_cache_access - Pin a cache so it can be accessed * @cache: The cache-level cookie @@ -278,6 +321,33 @@ void fscache_end_cache_access(struct fscache_cache *cache, enum fscache_access_t wake_up_var(&cache->n_accesses); } +/** + * fscache_withdraw_cache - Withdraw a cache from the active service + * @cache: The cache cookie + * + * Begin the process of withdrawing a cache from service. This stops new + * cache-level and volume-level accesses from taking place and waits for + * currently ongoing cache-level accesses to end. + */ +void fscache_withdraw_cache(struct fscache_cache *cache) +{ + int n_accesses; + + pr_notice("Withdrawing cache \"%s\" (%u objs)\n", + cache->name, atomic_read(&cache->object_count)); + + fscache_set_cache_state(cache, FSCACHE_CACHE_IS_WITHDRAWN); + + /* Allow wakeups on dec-to-0 */ + n_accesses = atomic_dec_return(&cache->n_accesses); + trace_fscache_access_cache(cache->debug_id, refcount_read(&cache->ref), + n_accesses, fscache_access_cache_unpin); + + wait_var_event(&cache->n_accesses, + atomic_read(&cache->n_accesses) == 0); +} +EXPORT_SYMBOL(fscache_withdraw_cache); + #ifdef CONFIG_PROC_FS static const char fscache_cache_states[NR__FSCACHE_CACHE_STATE] = "-PAEW"; diff --git a/include/linux/fscache-cache.h b/include/linux/fscache-cache.h index 66624407ba84..f78add6e7823 100644 --- a/include/linux/fscache-cache.h +++ b/include/linux/fscache-cache.h @@ -33,6 +33,7 @@ enum fscache_cache_state { * Cache cookie. */ struct fscache_cache { + const struct fscache_cache_ops *ops; struct list_head cache_link; /* Link in cache list */ void *cache_priv; /* Private cache data (or NULL) */ refcount_t ref; @@ -44,6 +45,14 @@ struct fscache_cache { char *name; }; +/* + * cache operations + */ +struct fscache_cache_ops { + /* name of cache provider */ + const char *name; +}; + extern struct workqueue_struct *fscache_wq; /* @@ -52,6 +61,10 @@ extern struct workqueue_struct *fscache_wq; extern struct rw_semaphore fscache_addremove_sem; extern struct fscache_cache *fscache_acquire_cache(const char *name); extern void fscache_relinquish_cache(struct fscache_cache *cache); +extern int fscache_add_cache(struct fscache_cache *cache, + const struct fscache_cache_ops *ops, + void *cache_priv); +extern void fscache_withdraw_cache(struct fscache_cache *cache); extern void fscache_end_volume_access(struct fscache_volume *volume, struct fscache_cookie *cookie,