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fscache: Implement functions add/remove a cache

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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     This marks the cache as withdrawn and thus prevents further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 <dhowells@redhat.com>
Reviewed-by: Jeff 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
This commit is contained in:
David Howells 2021-10-20 15:00:26 +01:00
parent a7733fb632
commit 2e0c76aee2
2 changed files with 83 additions and 0 deletions
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70
fs/fscache/cache.c
View File

@ -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";

13
include/linux/fscache-cache.h
View File

@ -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,