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![David Howells](/assets/img/avatar_default.png)
Fix object state machine to have separate work and wait states as that makes it easier to envision. There are now three kinds of state: (1) Work state. This is an execution state. No event processing is performed by a work state. The function attached to a work state returns a pointer indicating the next state to which the OSM should transition. Returning NO_TRANSIT repeats the current state, but goes back to the scheduler first. (2) Wait state. This is an event processing state. No execution is performed by a wait state. Wait states are just tables of "if event X occurs, clear it and transition to state Y". The dispatcher returns to the scheduler if none of the events in which the wait state has an interest are currently pending. (3) Out-of-band state. This is a special work state. Transitions to normal states can be overridden when an unexpected event occurs (eg. I/O error). Instead the dispatcher disables and clears the OOB event and transits to the specified work state. This then acts as an ordinary work state, though object->state points to the overridden destination. Returning NO_TRANSIT resumes the overridden transition. In addition, the states have names in their definitions, so there's no need for tables of state names. Further, the EV_REQUEUE event is no longer necessary as that is automatic for work states. Since the states are now separate structs rather than values in an enum, it's not possible to use comparisons other than (non-)equality between them, so use some object->flags to indicate what phase an object is in. The EV_RELEASE, EV_RETIRE and EV_WITHDRAW events have been squished into one (EV_KILL). An object flag now carries the information about retirement. Similarly, the RELEASING, RECYCLING and WITHDRAWING states have been merged into an KILL_OBJECT state and additional states have been added for handling waiting dependent objects (JUMPSTART_DEPS and KILL_DEPENDENTS). A state has also been added for synchronising with parent object initialisation (WAIT_FOR_PARENT) and another for initiating look up (PARENT_READY). Signed-off-by: David Howells <dhowells@redhat.com> Tested-By: Milosz Tanski <milosz@adfin.com> Acked-by: Jeff Layton <jlayton@redhat.com>
422 lines
11 KiB
C
422 lines
11 KiB
C
/* FS-Cache cache handling
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*
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* Copyright (C) 2007 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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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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#define FSCACHE_DEBUG_LEVEL CACHE
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#include <linux/module.h>
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#include <linux/slab.h>
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#include "internal.h"
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LIST_HEAD(fscache_cache_list);
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DECLARE_RWSEM(fscache_addremove_sem);
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DECLARE_WAIT_QUEUE_HEAD(fscache_cache_cleared_wq);
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EXPORT_SYMBOL(fscache_cache_cleared_wq);
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static LIST_HEAD(fscache_cache_tag_list);
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/*
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* look up a cache tag
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*/
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struct fscache_cache_tag *__fscache_lookup_cache_tag(const char *name)
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{
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struct fscache_cache_tag *tag, *xtag;
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/* firstly check for the existence of the tag under read lock */
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down_read(&fscache_addremove_sem);
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list_for_each_entry(tag, &fscache_cache_tag_list, link) {
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if (strcmp(tag->name, name) == 0) {
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atomic_inc(&tag->usage);
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up_read(&fscache_addremove_sem);
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return tag;
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}
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}
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up_read(&fscache_addremove_sem);
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/* the tag does not exist - create a candidate */
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xtag = kzalloc(sizeof(*xtag) + strlen(name) + 1, GFP_KERNEL);
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if (!xtag)
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/* return a dummy tag if out of memory */
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return ERR_PTR(-ENOMEM);
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atomic_set(&xtag->usage, 1);
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strcpy(xtag->name, name);
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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(tag, &fscache_cache_tag_list, link) {
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if (strcmp(tag->name, name) == 0) {
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atomic_inc(&tag->usage);
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up_write(&fscache_addremove_sem);
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kfree(xtag);
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return tag;
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}
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}
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list_add_tail(&xtag->link, &fscache_cache_tag_list);
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up_write(&fscache_addremove_sem);
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return xtag;
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}
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/*
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* release a reference to a cache tag
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*/
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void __fscache_release_cache_tag(struct fscache_cache_tag *tag)
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{
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if (tag != ERR_PTR(-ENOMEM)) {
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down_write(&fscache_addremove_sem);
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if (atomic_dec_and_test(&tag->usage))
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list_del_init(&tag->link);
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else
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tag = NULL;
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up_write(&fscache_addremove_sem);
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kfree(tag);
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}
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}
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/*
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* select a cache in which to store an object
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* - the cache addremove semaphore must be at least read-locked by the caller
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* - the object will never be an index
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*/
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struct fscache_cache *fscache_select_cache_for_object(
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struct fscache_cookie *cookie)
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{
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struct fscache_cache_tag *tag;
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struct fscache_object *object;
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struct fscache_cache *cache;
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_enter("");
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if (list_empty(&fscache_cache_list)) {
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_leave(" = NULL [no cache]");
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return NULL;
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}
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/* we check the parent to determine the cache to use */
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spin_lock(&cookie->lock);
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/* the first in the parent's backing list should be the preferred
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* cache */
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if (!hlist_empty(&cookie->backing_objects)) {
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object = hlist_entry(cookie->backing_objects.first,
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struct fscache_object, cookie_link);
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cache = object->cache;
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if (fscache_object_is_dying(object) ||
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test_bit(FSCACHE_IOERROR, &cache->flags))
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cache = NULL;
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spin_unlock(&cookie->lock);
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_leave(" = %p [parent]", cache);
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return cache;
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}
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/* the parent is unbacked */
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if (cookie->def->type != FSCACHE_COOKIE_TYPE_INDEX) {
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/* cookie not an index and is unbacked */
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spin_unlock(&cookie->lock);
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_leave(" = NULL [cookie ub,ni]");
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return NULL;
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}
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spin_unlock(&cookie->lock);
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if (!cookie->def->select_cache)
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goto no_preference;
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/* ask the netfs for its preference */
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tag = cookie->def->select_cache(cookie->parent->netfs_data,
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cookie->netfs_data);
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if (!tag)
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goto no_preference;
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if (tag == ERR_PTR(-ENOMEM)) {
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_leave(" = NULL [nomem tag]");
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return NULL;
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}
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if (!tag->cache) {
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_leave(" = NULL [unbacked tag]");
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return NULL;
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}
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if (test_bit(FSCACHE_IOERROR, &tag->cache->flags))
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return NULL;
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_leave(" = %p [specific]", tag->cache);
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return tag->cache;
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no_preference:
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/* netfs has no preference - just select first cache */
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cache = list_entry(fscache_cache_list.next,
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struct fscache_cache, link);
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_leave(" = %p [first]", cache);
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return cache;
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}
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/**
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* fscache_init_cache - Initialise a cache record
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* @cache: The cache record to be initialised
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* @ops: The cache operations to be installed in that record
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* @idfmt: Format string to define identifier
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* @...: sprintf-style arguments
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*
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* Initialise a record of a cache and fill in the name.
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*
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* See Documentation/filesystems/caching/backend-api.txt for a complete
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* description.
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*/
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void fscache_init_cache(struct fscache_cache *cache,
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const struct fscache_cache_ops *ops,
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const char *idfmt,
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...)
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{
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va_list va;
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memset(cache, 0, sizeof(*cache));
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cache->ops = ops;
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va_start(va, idfmt);
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vsnprintf(cache->identifier, sizeof(cache->identifier), idfmt, va);
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va_end(va);
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INIT_WORK(&cache->op_gc, fscache_operation_gc);
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INIT_LIST_HEAD(&cache->link);
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INIT_LIST_HEAD(&cache->object_list);
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INIT_LIST_HEAD(&cache->op_gc_list);
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spin_lock_init(&cache->object_list_lock);
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spin_lock_init(&cache->op_gc_list_lock);
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}
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EXPORT_SYMBOL(fscache_init_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 record describing the cache
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* @ifsdef: The record of the cache object describing the top-level index
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* @tagname: The tag describing this cache
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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.txt 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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struct fscache_object *ifsdef,
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const char *tagname)
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{
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struct fscache_cache_tag *tag;
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BUG_ON(!cache->ops);
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BUG_ON(!ifsdef);
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cache->flags = 0;
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ifsdef->event_mask =
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((1 << NR_FSCACHE_OBJECT_EVENTS) - 1) &
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~(1 << FSCACHE_OBJECT_EV_CLEARED);
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__set_bit(FSCACHE_OBJECT_IS_AVAILABLE, &ifsdef->flags);
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if (!tagname)
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tagname = cache->identifier;
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BUG_ON(!tagname[0]);
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_enter("{%s.%s},,%s", cache->ops->name, cache->identifier, tagname);
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/* we use the cache tag to uniquely identify caches */
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tag = __fscache_lookup_cache_tag(tagname);
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if (IS_ERR(tag))
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goto nomem;
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if (test_and_set_bit(FSCACHE_TAG_RESERVED, &tag->flags))
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goto tag_in_use;
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cache->kobj = kobject_create_and_add(tagname, fscache_root);
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if (!cache->kobj)
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goto error;
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ifsdef->cookie = &fscache_fsdef_index;
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ifsdef->cache = cache;
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cache->fsdef = ifsdef;
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down_write(&fscache_addremove_sem);
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tag->cache = cache;
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cache->tag = tag;
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/* add the cache to the list */
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list_add(&cache->link, &fscache_cache_list);
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/* add the cache's netfs definition index object to the cache's
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* list */
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spin_lock(&cache->object_list_lock);
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list_add_tail(&ifsdef->cache_link, &cache->object_list);
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spin_unlock(&cache->object_list_lock);
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fscache_objlist_add(ifsdef);
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/* add the cache's netfs definition index object to the top level index
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* cookie as a known backing object */
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spin_lock(&fscache_fsdef_index.lock);
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hlist_add_head(&ifsdef->cookie_link,
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&fscache_fsdef_index.backing_objects);
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atomic_inc(&fscache_fsdef_index.usage);
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/* done */
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spin_unlock(&fscache_fsdef_index.lock);
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up_write(&fscache_addremove_sem);
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printk(KERN_NOTICE "FS-Cache: Cache \"%s\" added (type %s)\n",
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cache->tag->name, cache->ops->name);
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kobject_uevent(cache->kobj, KOBJ_ADD);
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_leave(" = 0 [%s]", cache->identifier);
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return 0;
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tag_in_use:
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printk(KERN_ERR "FS-Cache: Cache tag '%s' already in use\n", tagname);
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__fscache_release_cache_tag(tag);
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_leave(" = -EXIST");
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return -EEXIST;
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error:
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__fscache_release_cache_tag(tag);
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_leave(" = -EINVAL");
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return -EINVAL;
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nomem:
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_leave(" = -ENOMEM");
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return -ENOMEM;
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}
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EXPORT_SYMBOL(fscache_add_cache);
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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.txt 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 (!test_and_set_bit(FSCACHE_IOERROR, &cache->flags))
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printk(KERN_ERR "FS-Cache:"
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" Cache '%s' stopped due to I/O error\n",
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cache->ops->name);
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}
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EXPORT_SYMBOL(fscache_io_error);
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/*
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* request withdrawal of all the objects in a cache
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* - all the objects being withdrawn are moved onto the supplied list
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*/
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static void fscache_withdraw_all_objects(struct fscache_cache *cache,
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struct list_head *dying_objects)
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{
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struct fscache_object *object;
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while (!list_empty(&cache->object_list)) {
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spin_lock(&cache->object_list_lock);
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if (!list_empty(&cache->object_list)) {
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object = list_entry(cache->object_list.next,
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struct fscache_object, cache_link);
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list_move_tail(&object->cache_link, dying_objects);
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_debug("withdraw %p", object->cookie);
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/* This must be done under object_list_lock to prevent
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* a race with fscache_drop_object().
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*/
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fscache_raise_event(object, FSCACHE_OBJECT_EV_KILL);
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}
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spin_unlock(&cache->object_list_lock);
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cond_resched();
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}
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}
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/**
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* fscache_withdraw_cache - Withdraw a cache from the active service
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* @cache: The record describing the cache
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*
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* Withdraw a cache from service, unbinding all its cache objects from the
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* netfs cookies they're currently representing.
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*
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* See Documentation/filesystems/caching/backend-api.txt for a complete
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* description.
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*/
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void fscache_withdraw_cache(struct fscache_cache *cache)
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{
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LIST_HEAD(dying_objects);
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_enter("");
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printk(KERN_NOTICE "FS-Cache: Withdrawing cache \"%s\"\n",
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cache->tag->name);
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/* make the cache unavailable for cookie acquisition */
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if (test_and_set_bit(FSCACHE_CACHE_WITHDRAWN, &cache->flags))
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BUG();
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down_write(&fscache_addremove_sem);
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list_del_init(&cache->link);
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cache->tag->cache = NULL;
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up_write(&fscache_addremove_sem);
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/* make sure all pages pinned by operations on behalf of the netfs are
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* written to disk */
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fscache_stat(&fscache_n_cop_sync_cache);
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cache->ops->sync_cache(cache);
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fscache_stat_d(&fscache_n_cop_sync_cache);
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/* dissociate all the netfs pages backed by this cache from the block
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* mappings in the cache */
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fscache_stat(&fscache_n_cop_dissociate_pages);
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cache->ops->dissociate_pages(cache);
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fscache_stat_d(&fscache_n_cop_dissociate_pages);
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/* we now have to destroy all the active objects pertaining to this
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* cache - which we do by passing them off to thread pool to be
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* disposed of */
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_debug("destroy");
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fscache_withdraw_all_objects(cache, &dying_objects);
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/* wait for all extant objects to finish their outstanding operations
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* and go away */
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_debug("wait for finish");
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wait_event(fscache_cache_cleared_wq,
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atomic_read(&cache->object_count) == 0);
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_debug("wait for clearance");
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wait_event(fscache_cache_cleared_wq,
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list_empty(&cache->object_list));
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_debug("cleared");
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ASSERT(list_empty(&dying_objects));
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kobject_put(cache->kobj);
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clear_bit(FSCACHE_TAG_RESERVED, &cache->tag->flags);
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fscache_release_cache_tag(cache->tag);
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cache->tag = NULL;
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_leave("");
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}
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EXPORT_SYMBOL(fscache_withdraw_cache);
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