5d00e426f9
Implement a very simple cookie state machine to handle lookup, invalidation, withdrawal, relinquishment and, to be added later, commit on LRU discard. Three cache methods are provided: ->lookup_cookie() to look up and, if necessary, create a data storage object; ->withdraw_cookie() to free the resources associated with that object and potentially delete it; and ->prepare_to_write(), to do prepare for changes to the cached data to be modified locally. Changes ======= ver #3: - Fix a race between LRU discard and relinquishment whereby the former would override the latter and thus the latter would never happen[1]. ver #2: - Don't hold n_accesses elevated whilst cache is bound to a cookie, but rather add a flag that prevents the state machine from being queued when n_accesses reaches 0. 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/599331.1639410068@warthog.procyon.org.uk/ [1] Link: https://lore.kernel.org/r/163819599657.215744.15799615296912341745.stgit@warthog.procyon.org.uk/ # v1 Link: https://lore.kernel.org/r/163906903925.143852.1805855338154353867.stgit@warthog.procyon.org.uk/ # v2 Link: https://lore.kernel.org/r/163967105456.1823006.14730395299835841776.stgit@warthog.procyon.org.uk/ # v3 Link: https://lore.kernel.org/r/164021510706.640689.7961423370243272583.stgit@warthog.procyon.org.uk/ # v4
128 lines
4 KiB
C
128 lines
4 KiB
C
/* SPDX-License-Identifier: GPL-2.0-or-later */
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/* General filesystem caching backing cache interface
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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 (dhowells@redhat.com)
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*
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* NOTE!!! See:
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*
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* Documentation/filesystems/caching/backend-api.rst
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*
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* for a description of the cache backend interface declared here.
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*/
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#ifndef _LINUX_FSCACHE_CACHE_H
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#define _LINUX_FSCACHE_CACHE_H
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#include <linux/fscache.h>
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enum fscache_cache_trace;
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enum fscache_cookie_trace;
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enum fscache_access_trace;
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enum fscache_cache_state {
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FSCACHE_CACHE_IS_NOT_PRESENT, /* No cache is present for this name */
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FSCACHE_CACHE_IS_PREPARING, /* A cache is preparing to come live */
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FSCACHE_CACHE_IS_ACTIVE, /* Attached cache is active and can be used */
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FSCACHE_CACHE_GOT_IOERROR, /* Attached cache stopped on I/O error */
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FSCACHE_CACHE_IS_WITHDRAWN, /* Attached cache is being withdrawn */
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#define NR__FSCACHE_CACHE_STATE (FSCACHE_CACHE_IS_WITHDRAWN + 1)
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};
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/*
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* Cache cookie.
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*/
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struct fscache_cache {
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const struct fscache_cache_ops *ops;
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struct list_head cache_link; /* Link in cache list */
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void *cache_priv; /* Private cache data (or NULL) */
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refcount_t ref;
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atomic_t n_volumes; /* Number of active volumes; */
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atomic_t n_accesses; /* Number of in-progress accesses on the cache */
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atomic_t object_count; /* no. of live objects in this cache */
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unsigned int debug_id;
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enum fscache_cache_state state;
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char *name;
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};
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/*
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* cache operations
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*/
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struct fscache_cache_ops {
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/* name of cache provider */
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const char *name;
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/* Acquire a volume */
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void (*acquire_volume)(struct fscache_volume *volume);
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/* Free the cache's data attached to a volume */
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void (*free_volume)(struct fscache_volume *volume);
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/* Look up a cookie in the cache */
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bool (*lookup_cookie)(struct fscache_cookie *cookie);
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/* Withdraw an object without any cookie access counts held */
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void (*withdraw_cookie)(struct fscache_cookie *cookie);
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/* Prepare to write to a live cache object */
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void (*prepare_to_write)(struct fscache_cookie *cookie);
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};
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extern struct workqueue_struct *fscache_wq;
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/*
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* out-of-line cache backend functions
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*/
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extern struct rw_semaphore fscache_addremove_sem;
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extern struct fscache_cache *fscache_acquire_cache(const char *name);
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extern void fscache_relinquish_cache(struct fscache_cache *cache);
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extern 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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extern void fscache_withdraw_cache(struct fscache_cache *cache);
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extern void fscache_withdraw_volume(struct fscache_volume *volume);
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extern void fscache_withdraw_cookie(struct fscache_cookie *cookie);
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extern void fscache_io_error(struct fscache_cache *cache);
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extern void fscache_end_volume_access(struct fscache_volume *volume,
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struct fscache_cookie *cookie,
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enum fscache_access_trace why);
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extern struct fscache_cookie *fscache_get_cookie(struct fscache_cookie *cookie,
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enum fscache_cookie_trace where);
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extern void fscache_put_cookie(struct fscache_cookie *cookie,
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enum fscache_cookie_trace where);
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extern void fscache_end_cookie_access(struct fscache_cookie *cookie,
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enum fscache_access_trace why);
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extern void fscache_cookie_lookup_negative(struct fscache_cookie *cookie);
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extern void fscache_caching_failed(struct fscache_cookie *cookie);
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/**
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* fscache_cookie_state - Read the state of a cookie
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* @cookie: The cookie to query
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*
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* Get the state of a cookie, imposing an ordering between the cookie contents
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* and the state value. Paired with fscache_set_cookie_state().
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*/
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static inline
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enum fscache_cookie_state fscache_cookie_state(struct fscache_cookie *cookie)
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{
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return smp_load_acquire(&cookie->state);
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}
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/**
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* fscache_get_key - Get a pointer to the cookie key
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* @cookie: The cookie to query
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*
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* Return a pointer to the where a cookie's key is stored.
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*/
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static inline void *fscache_get_key(struct fscache_cookie *cookie)
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{
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if (cookie->key_len <= sizeof(cookie->inline_key))
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return cookie->inline_key;
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else
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return cookie->key;
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}
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#endif /* _LINUX_FSCACHE_CACHE_H */
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