Commit 2e0c76ae authored by David Howells's avatar David Howells
Browse files

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     This marks the cache as withdrawn and thus prevents further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: default avatarDavid Howells <dhowells@redhat.com>
Reviewed-by: default avatarJeff Layton <jlayton@kernel.org>
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
parent a7733fb6

fs/fscache/cache.c

+70 −0
Original line number Diff line number Diff line
@@ -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";

include/linux/fscache-cache.h

+13 −0
Original line number Diff line number Diff line
@@ -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,