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428 lines
12 KiB
428 lines
12 KiB
// SPDX-License-Identifier: GPL-2.0-or-later |
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/* FS-Cache cache handling |
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* |
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* Copyright (C) 2021 Red Hat, Inc. All Rights Reserved. |
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* Written by David Howells ([email protected]) |
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*/ |
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#define FSCACHE_DEBUG_LEVEL CACHE |
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#include <linux/export.h> |
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#include <linux/slab.h> |
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#include "internal.h" |
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static LIST_HEAD(fscache_caches); |
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DECLARE_RWSEM(fscache_addremove_sem); |
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EXPORT_SYMBOL(fscache_addremove_sem); |
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DECLARE_WAIT_QUEUE_HEAD(fscache_clearance_waiters); |
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EXPORT_SYMBOL(fscache_clearance_waiters); |
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static atomic_t fscache_cache_debug_id; |
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/* |
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* Allocate a cache cookie. |
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*/ |
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static struct fscache_cache *fscache_alloc_cache(const char *name) |
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{ |
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struct fscache_cache *cache; |
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cache = kzalloc(sizeof(*cache), GFP_KERNEL); |
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if (cache) { |
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if (name) { |
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cache->name = kstrdup(name, GFP_KERNEL); |
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if (!cache->name) { |
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kfree(cache); |
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return NULL; |
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} |
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} |
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refcount_set(&cache->ref, 1); |
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INIT_LIST_HEAD(&cache->cache_link); |
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cache->debug_id = atomic_inc_return(&fscache_cache_debug_id); |
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} |
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return cache; |
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} |
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static bool fscache_get_cache_maybe(struct fscache_cache *cache, |
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enum fscache_cache_trace where) |
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{ |
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bool success; |
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int ref; |
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success = __refcount_inc_not_zero(&cache->ref, &ref); |
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if (success) |
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trace_fscache_cache(cache->debug_id, ref + 1, where); |
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return success; |
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} |
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/* |
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* Look up a cache cookie. |
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*/ |
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struct fscache_cache *fscache_lookup_cache(const char *name, bool is_cache) |
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{ |
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struct fscache_cache *candidate, *cache, *unnamed = NULL; |
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/* firstly check for the existence of the cache under read lock */ |
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down_read(&fscache_addremove_sem); |
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list_for_each_entry(cache, &fscache_caches, cache_link) { |
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if (cache->name && name && strcmp(cache->name, name) == 0 && |
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fscache_get_cache_maybe(cache, fscache_cache_get_acquire)) |
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goto got_cache_r; |
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if (!cache->name && !name && |
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fscache_get_cache_maybe(cache, fscache_cache_get_acquire)) |
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goto got_cache_r; |
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} |
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if (!name) { |
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list_for_each_entry(cache, &fscache_caches, cache_link) { |
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if (cache->name && |
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fscache_get_cache_maybe(cache, fscache_cache_get_acquire)) |
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goto got_cache_r; |
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} |
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} |
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up_read(&fscache_addremove_sem); |
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/* the cache does not exist - create a candidate */ |
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candidate = fscache_alloc_cache(name); |
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if (!candidate) |
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return ERR_PTR(-ENOMEM); |
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/* write lock, search again and add if still not present */ |
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down_write(&fscache_addremove_sem); |
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list_for_each_entry(cache, &fscache_caches, cache_link) { |
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if (cache->name && name && strcmp(cache->name, name) == 0 && |
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fscache_get_cache_maybe(cache, fscache_cache_get_acquire)) |
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goto got_cache_w; |
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if (!cache->name) { |
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unnamed = cache; |
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if (!name && |
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fscache_get_cache_maybe(cache, fscache_cache_get_acquire)) |
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goto got_cache_w; |
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} |
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} |
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if (unnamed && is_cache && |
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fscache_get_cache_maybe(unnamed, fscache_cache_get_acquire)) |
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goto use_unnamed_cache; |
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if (!name) { |
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list_for_each_entry(cache, &fscache_caches, cache_link) { |
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if (cache->name && |
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fscache_get_cache_maybe(cache, fscache_cache_get_acquire)) |
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goto got_cache_w; |
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} |
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} |
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list_add_tail(&candidate->cache_link, &fscache_caches); |
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trace_fscache_cache(candidate->debug_id, |
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refcount_read(&candidate->ref), |
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fscache_cache_new_acquire); |
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up_write(&fscache_addremove_sem); |
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return candidate; |
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got_cache_r: |
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up_read(&fscache_addremove_sem); |
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return cache; |
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use_unnamed_cache: |
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cache = unnamed; |
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cache->name = candidate->name; |
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candidate->name = NULL; |
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got_cache_w: |
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up_write(&fscache_addremove_sem); |
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kfree(candidate->name); |
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kfree(candidate); |
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return cache; |
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} |
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/** |
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* fscache_acquire_cache - Acquire a cache-level cookie. |
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* @name: The name of the cache. |
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* |
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* Get a cookie to represent an actual cache. If a name is given and there is |
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* a nameless cache record available, this will acquire that and set its name, |
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* directing all the volumes using it to this cache. |
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* |
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* The cache will be switched over to the preparing state if not currently in |
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* use, otherwise -EBUSY will be returned. |
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*/ |
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struct fscache_cache *fscache_acquire_cache(const char *name) |
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{ |
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struct fscache_cache *cache; |
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ASSERT(name); |
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cache = fscache_lookup_cache(name, true); |
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if (IS_ERR(cache)) |
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return cache; |
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if (!fscache_set_cache_state_maybe(cache, |
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FSCACHE_CACHE_IS_NOT_PRESENT, |
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FSCACHE_CACHE_IS_PREPARING)) { |
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pr_warn("Cache tag %s in use\n", name); |
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fscache_put_cache(cache, fscache_cache_put_cache); |
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return ERR_PTR(-EBUSY); |
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} |
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return cache; |
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} |
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EXPORT_SYMBOL(fscache_acquire_cache); |
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/** |
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* fscache_put_cache - Release a cache-level cookie. |
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* @cache: The cache cookie to be released |
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* @where: An indication of where the release happened |
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* |
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* Release the caller's reference on a cache-level cookie. The @where |
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* indication should give information about the circumstances in which the call |
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* occurs and will be logged through a tracepoint. |
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*/ |
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void fscache_put_cache(struct fscache_cache *cache, |
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enum fscache_cache_trace where) |
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{ |
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unsigned int debug_id = cache->debug_id; |
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bool zero; |
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int ref; |
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if (IS_ERR_OR_NULL(cache)) |
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return; |
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zero = __refcount_dec_and_test(&cache->ref, &ref); |
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trace_fscache_cache(debug_id, ref - 1, where); |
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if (zero) { |
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down_write(&fscache_addremove_sem); |
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list_del_init(&cache->cache_link); |
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up_write(&fscache_addremove_sem); |
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kfree(cache->name); |
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kfree(cache); |
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} |
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} |
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/** |
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* fscache_relinquish_cache - Reset cache state and release cookie |
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* @cache: The cache cookie to be released |
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* |
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* Reset the state of a cache and release the caller's reference on a cache |
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* cookie. |
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*/ |
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void fscache_relinquish_cache(struct fscache_cache *cache) |
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{ |
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enum fscache_cache_trace where = |
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(cache->state == FSCACHE_CACHE_IS_PREPARING) ? |
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fscache_cache_put_prep_failed : |
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fscache_cache_put_relinquish; |
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cache->ops = NULL; |
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cache->cache_priv = NULL; |
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fscache_set_cache_state(cache, FSCACHE_CACHE_IS_NOT_PRESENT); |
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fscache_put_cache(cache, where); |
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} |
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EXPORT_SYMBOL(fscache_relinquish_cache); |
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/** |
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* fscache_add_cache - Declare a cache as being open for business |
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* @cache: The cache-level cookie representing the cache |
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* @ops: Table of cache operations to use |
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* @cache_priv: Private data for the cache record |
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* |
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* Add a cache to the system, making it available for netfs's to use. |
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* |
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* See Documentation/filesystems/caching/backend-api.rst for a complete |
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* description. |
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*/ |
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int fscache_add_cache(struct fscache_cache *cache, |
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const struct fscache_cache_ops *ops, |
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void *cache_priv) |
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{ |
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int n_accesses; |
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_enter("{%s,%s}", ops->name, cache->name); |
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BUG_ON(fscache_cache_state(cache) != FSCACHE_CACHE_IS_PREPARING); |
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/* Get a ref on the cache cookie and keep its n_accesses counter raised |
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* by 1 to prevent wakeups from transitioning it to 0 until we're |
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* withdrawing caching services from it. |
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*/ |
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n_accesses = atomic_inc_return(&cache->n_accesses); |
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trace_fscache_access_cache(cache->debug_id, refcount_read(&cache->ref), |
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n_accesses, fscache_access_cache_pin); |
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down_write(&fscache_addremove_sem); |
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cache->ops = ops; |
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cache->cache_priv = cache_priv; |
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fscache_set_cache_state(cache, FSCACHE_CACHE_IS_ACTIVE); |
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up_write(&fscache_addremove_sem); |
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pr_notice("Cache \"%s\" added (type %s)\n", cache->name, ops->name); |
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_leave(" = 0 [%s]", cache->name); |
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return 0; |
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} |
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EXPORT_SYMBOL(fscache_add_cache); |
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/** |
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* fscache_begin_cache_access - Pin a cache so it can be accessed |
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* @cache: The cache-level cookie |
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* @why: An indication of the circumstances of the access for tracing |
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* |
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* Attempt to pin the cache to prevent it from going away whilst we're |
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* accessing it and returns true if successful. This works as follows: |
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* |
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* (1) If the cache tests as not live (state is not FSCACHE_CACHE_IS_ACTIVE), |
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* then we return false to indicate access was not permitted. |
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* |
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* (2) If the cache tests as live, then we increment the n_accesses count and |
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* then recheck the liveness, ending the access if it ceased to be live. |
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* |
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* (3) When we end the access, we decrement n_accesses and wake up the any |
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* waiters if it reaches 0. |
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* |
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* (4) Whilst the cache is caching, n_accesses is kept artificially |
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* incremented to prevent wakeups from happening. |
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* |
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* (5) When the cache is taken offline, the state is changed to prevent new |
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* accesses, n_accesses is decremented and we wait for n_accesses to |
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* become 0. |
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*/ |
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bool fscache_begin_cache_access(struct fscache_cache *cache, enum fscache_access_trace why) |
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{ |
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int n_accesses; |
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if (!fscache_cache_is_live(cache)) |
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return false; |
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n_accesses = atomic_inc_return(&cache->n_accesses); |
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smp_mb__after_atomic(); /* Reread live flag after n_accesses */ |
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trace_fscache_access_cache(cache->debug_id, refcount_read(&cache->ref), |
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n_accesses, why); |
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if (!fscache_cache_is_live(cache)) { |
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fscache_end_cache_access(cache, fscache_access_unlive); |
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return false; |
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} |
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return true; |
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} |
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/** |
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* fscache_end_cache_access - Unpin a cache at the end of an access. |
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* @cache: The cache-level cookie |
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* @why: An indication of the circumstances of the access for tracing |
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* |
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* Unpin a cache after we've accessed it. The @why indicator is merely |
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* provided for tracing purposes. |
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*/ |
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void fscache_end_cache_access(struct fscache_cache *cache, enum fscache_access_trace why) |
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{ |
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int n_accesses; |
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smp_mb__before_atomic(); |
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n_accesses = atomic_dec_return(&cache->n_accesses); |
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trace_fscache_access_cache(cache->debug_id, refcount_read(&cache->ref), |
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n_accesses, why); |
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if (n_accesses == 0) |
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wake_up_var(&cache->n_accesses); |
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} |
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/** |
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* fscache_io_error - Note a cache I/O error |
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* @cache: The record describing the cache |
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* |
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* Note that an I/O error occurred in a cache and that it should no longer be |
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* used for anything. This also reports the error into the kernel log. |
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* |
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* See Documentation/filesystems/caching/backend-api.rst for a complete |
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* description. |
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*/ |
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void fscache_io_error(struct fscache_cache *cache) |
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{ |
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if (fscache_set_cache_state_maybe(cache, |
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FSCACHE_CACHE_IS_ACTIVE, |
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FSCACHE_CACHE_GOT_IOERROR)) |
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pr_err("Cache '%s' stopped due to I/O error\n", |
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cache->name); |
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} |
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EXPORT_SYMBOL(fscache_io_error); |
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/** |
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* fscache_withdraw_cache - Withdraw a cache from the active service |
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* @cache: The cache cookie |
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* |
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* Begin the process of withdrawing a cache from service. This stops new |
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* cache-level and volume-level accesses from taking place and waits for |
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* currently ongoing cache-level accesses to end. |
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*/ |
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void fscache_withdraw_cache(struct fscache_cache *cache) |
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{ |
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int n_accesses; |
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pr_notice("Withdrawing cache \"%s\" (%u objs)\n", |
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cache->name, atomic_read(&cache->object_count)); |
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fscache_set_cache_state(cache, FSCACHE_CACHE_IS_WITHDRAWN); |
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/* Allow wakeups on dec-to-0 */ |
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n_accesses = atomic_dec_return(&cache->n_accesses); |
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trace_fscache_access_cache(cache->debug_id, refcount_read(&cache->ref), |
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n_accesses, fscache_access_cache_unpin); |
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wait_var_event(&cache->n_accesses, |
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atomic_read(&cache->n_accesses) == 0); |
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} |
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EXPORT_SYMBOL(fscache_withdraw_cache); |
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#ifdef CONFIG_PROC_FS |
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static const char fscache_cache_states[NR__FSCACHE_CACHE_STATE] = "-PAEW"; |
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/* |
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* Generate a list of caches in /proc/fs/fscache/caches |
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*/ |
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static int fscache_caches_seq_show(struct seq_file *m, void *v) |
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{ |
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struct fscache_cache *cache; |
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if (v == &fscache_caches) { |
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seq_puts(m, |
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"CACHE REF VOLS OBJS ACCES S NAME\n" |
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"======== ===== ===== ===== ===== = ===============\n" |
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); |
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return 0; |
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} |
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cache = list_entry(v, struct fscache_cache, cache_link); |
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seq_printf(m, |
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"%08x %5d %5d %5d %5d %c %s\n", |
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cache->debug_id, |
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refcount_read(&cache->ref), |
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atomic_read(&cache->n_volumes), |
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atomic_read(&cache->object_count), |
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atomic_read(&cache->n_accesses), |
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fscache_cache_states[cache->state], |
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cache->name ?: "-"); |
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return 0; |
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} |
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static void *fscache_caches_seq_start(struct seq_file *m, loff_t *_pos) |
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__acquires(fscache_addremove_sem) |
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{ |
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down_read(&fscache_addremove_sem); |
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return seq_list_start_head(&fscache_caches, *_pos); |
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} |
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static void *fscache_caches_seq_next(struct seq_file *m, void *v, loff_t *_pos) |
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{ |
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return seq_list_next(v, &fscache_caches, _pos); |
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} |
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static void fscache_caches_seq_stop(struct seq_file *m, void *v) |
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__releases(fscache_addremove_sem) |
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{ |
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up_read(&fscache_addremove_sem); |
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} |
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const struct seq_operations fscache_caches_seq_ops = { |
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.start = fscache_caches_seq_start, |
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.next = fscache_caches_seq_next, |
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.stop = fscache_caches_seq_stop, |
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.show = fscache_caches_seq_show, |
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}; |
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#endif /* CONFIG_PROC_FS */
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