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| -rw-r--r-- | Documentation/filesystems/caching/backend-api.txt | 664 | ||||
| -rw-r--r-- | include/linux/fscache-cache.h | 509 |
2 files changed, 1173 insertions, 0 deletions
diff --git a/Documentation/filesystems/caching/backend-api.txt b/Documentation/filesystems/caching/backend-api.txt new file mode 100644 index 00000000000..17723053aa9 --- /dev/null +++ b/Documentation/filesystems/caching/backend-api.txt @@ -0,0 +1,664 @@ + ========================== + FS-CACHE CACHE BACKEND API + ========================== + +The FS-Cache system provides an API by which actual caches can be supplied to +FS-Cache for it to then serve out to network filesystems and other interested +parties. + +This API is declared in <linux/fscache-cache.h>. + + +==================================== +INITIALISING AND REGISTERING A CACHE +==================================== + +To start off, a cache definition must be initialised and registered for each +cache the backend wants to make available. For instance, CacheFS does this in +the fill_super() operation on mounting. + +The cache definition (struct fscache_cache) should be initialised by calling: + + void fscache_init_cache(struct fscache_cache *cache, + struct fscache_cache_ops *ops, + const char *idfmt, + ...); + +Where: + + (*) "cache" is a pointer to the cache definition; + + (*) "ops" is a pointer to the table of operations that the backend supports on + this cache; and + + (*) "idfmt" is a format and printf-style arguments for constructing a label + for the cache. + + +The cache should then be registered with FS-Cache by passing a pointer to the +previously initialised cache definition to: + + int fscache_add_cache(struct fscache_cache *cache, + struct fscache_object *fsdef, + const char *tagname); + +Two extra arguments should also be supplied: + + (*) "fsdef" which should point to the object representation for the FS-Cache + master index in this cache. Netfs primary index entries will be created + here. FS-Cache keeps the caller's reference to the index object if + successful and will release it upon withdrawal of the cache. + + (*) "tagname" which, if given, should be a text string naming this cache. If + this is NULL, the identifier will be used instead. For CacheFS, the + identifier is set to name the underlying block device and the tag can be + supplied by mount. + +This function may return -ENOMEM if it ran out of memory or -EEXIST if the tag +is already in use. 0 will be returned on success. + + +===================== +UNREGISTERING A CACHE +===================== + +A cache can be withdrawn from the system by calling this function with a +pointer to the cache definition: + + void fscache_withdraw_cache(struct fscache_cache *cache); + +In CacheFS's case, this is called by put_super(). + + +======== +SECURITY +======== + +The cache methods are executed one of two contexts: + + (1) that of the userspace process that issued the netfs operation that caused + the cache method to be invoked, or + + (2) that of one of the processes in the FS-Cache thread pool. + +In either case, this may not be an appropriate context in which to access the +cache. + +The calling process's fsuid, fsgid and SELinux security identities may need to +be masqueraded for the duration of the cache driver's access to the cache. +This is left to the cache to handle; FS-Cache makes no effort in this regard. + + +=================================== +CONTROL AND STATISTICS PRESENTATION +=================================== + +The cache may present data to the outside world through FS-Cache's interfaces +in sysfs and procfs - the former for control and the latter for statistics. + +A sysfs directory called /sys/fs/fscache/<cachetag>/ is created if CONFIG_SYSFS +is enabled. This is accessible through the kobject struct fscache_cache::kobj +and is for use by the cache as it sees fit. + +The cache driver may create itself a directory named for the cache type in the +/proc/fs/fscache/ directory. This is available if CONFIG_FSCACHE_PROC is +enabled and is accessible through: + + struct proc_dir_entry *proc_fscache; + + +======================== +RELEVANT DATA STRUCTURES +======================== + + (*) Index/Data file FS-Cache representation cookie: + + struct fscache_cookie { + struct fscache_object_def *def; + struct fscache_netfs *netfs; + void *netfs_data; + ... + }; + + The fields that might be of use to the backend describe the object + definition, the netfs definition and the netfs's data for this cookie. + The object definition contain functions supplied by the netfs for loading + and matching index entries; these are required to provide some of the + cache operations. + + + (*) In-cache object representation: + + struct fscache_object { + int debug_id; + enum { + FSCACHE_OBJECT_RECYCLING, + ... + } state; + spinlock_t lock + struct fscache_cache *cache; + struct fscache_cookie *cookie; + ... + }; + + Structures of this type should be allocated by the cache backend and + passed to FS-Cache when requested by the appropriate cache operation. In + the case of CacheFS, they're embedded in CacheFS's internal object + structures. + + The debug_id is a simple integer that can be used in debugging messages + that refer to a particular object. In such a case it should be printed + using "OBJ%x" to be consistent with FS-Cache. + + Each object contains a pointer to the cookie that represents the object it + is backing. An object should retired when put_object() is called if it is + in state FSCACHE_OBJECT_RECYCLING. The fscache_object struct should be + initialised by calling fscache_object_init(object). + + + (*) FS-Cache operation record: + + struct fscache_operation { + atomic_t usage; + struct fscache_object *object; + unsigned long flags; + #define FSCACHE_OP_EXCLUSIVE + void (*processor)(struct fscache_operation *op); + void (*release)(struct fscache_operation *op); + ... + }; + + FS-Cache has a pool of threads that it uses to give CPU time to the + various asynchronous operations that need to be done as part of driving + the cache. These are represented by the above structure. The processor + method is called to give the op CPU time, and the release method to get + rid of it when its usage count reaches 0. + + An operation can be made exclusive upon an object by setting the + appropriate flag before enqueuing it with fscache_enqueue_operation(). If + an operation needs more processing time, it should be enqueued again. + + + (*) FS-Cache retrieval operation record: + + struct fscache_retrieval { + struct fscache_operation op; + struct address_space *mapping; + struct list_head *to_do; + ... + }; + + A structure of this type is allocated by FS-Cache to record retrieval and + allocation requests made by the netfs. This struct is then passed to the + backend to do the operation. The backend may get extra refs to it by + calling fscache_get_retrieval() and refs may be discarded by calling + fscache_put_retrieval(). + + A retrieval operation can be used by the backend to do retrieval work. To + do this, the retrieval->op.processor method pointer should be set + appropriately by the backend and fscache_enqueue_retrieval() called to + submit it to the thread pool. CacheFiles, for example, uses this to queue + page examination when it detects PG_lock being cleared. + + The to_do field is an empty list available for the cache backend to use as + it sees fit. + + + (*) FS-Cache storage operation record: + + struct fscache_storage { + struct fscache_operation op; + pgoff_t store_limit; + ... + }; + + A structure of this type is allocated by FS-Cache to record outstanding + writes to be made. FS-Cache itself enqueues this operation and invokes + the write_page() method on the object at appropriate times to effect + storage. + + +================ +CACHE OPERATIONS +================ + +The cache backend provides FS-Cache with a table of operations that can be +performed on the denizens of the cache. These are held in a structure of type: + + struct fscache_cache_ops + + (*) Name of cache provider [mandatory]: + + const char *name + + This isn't strictly an operation, but should be pointed at a string naming + the backend. + + + (*) Allocate a new object [mandatory]: + + struct fscache_object *(*alloc_object)(struct fscache_cache *cache, + struct fscache_cookie *cookie) + + This method is used to allocate a cache object representation to back a + cookie in a particular cache. fscache_object_init() should be called on + the object to initialise it prior to returning. + + This function may also be used to parse the index key to be used for + multiple lookup calls to turn it into a more convenient form. FS-Cache + will call the lookup_complete() method to allow the cache to release the + form once lookup is complete or aborted. + + + (*) Look up and create object [mandatory]: + + void (*lookup_object)(struct fscache_object *object) + + This method is used to look up an object, given that the object is already + allocated and attached to the cookie. This should instantiate that object + in the cache if it can. + + The method should call fscache_object_lookup_negative() as soon as + possible if it determines the object doesn't exist in the cache. If the + object is found to exist and the netfs indicates that it is valid then + fscache_obtained_object() should be called once the object is in a + position to have data stored in it. Similarly, fscache_obtained_object() + should also be called once a non-present object has been created. + + If a lookup error occurs, fscache_object_lookup_error() should be called + to abort the lookup of that object. + + + (*) Release lookup data [mandatory]: + + void (*lookup_complete)(struct fscache_object *object) + + This method is called to ask the cache to release any resources it was + using to perform a lookup. + + + (*) Increment object refcount [mandatory]: + + struct fscache_object *(*grab_object)(struct fscache_object *object) + + This method is called to increment the reference count on an object. It + may fail (for instance if the cache is being withdrawn) by returning NULL. + It should return the object pointer if successful. + + + (*) Lock/Unlock object [mandatory]: + + void (*lock_object)(struct fscache_object *object) + void (*unlock_object)(struct fscache_object *object) + + These methods are used to exclusively lock an object. It must be possible + to schedule with the lock held, so a spinlock isn't sufficient. + + + (*) Pin/Unpin object [optional]: + + int (*pin_object)(struct fscache_object *object) + void (*unpin_object)(struct fscache_object *object) + + These methods are used to pin an object into the cache. Once pinned an + object cannot be reclaimed to make space. Return -ENOSPC if there's not + enough space in the cache to permit this. + + + (*) Update object [mandatory]: + + int (*update_object)(struct fscache_object *object) + + This is called to update the index entry for the specified object. The + new information should be in object->cookie->netfs_data. This can be + obtained by calling object->cookie->def->get_aux()/get_attr(). + + + (*) Discard object [mandatory]: + + void (*drop_object)(struct fscache_object *object) + + This method is called to indicate that an object has been unbound from its + cookie, and that the cache should release the object's resources and + retire it if it's in state FSCACHE_OBJECT_RECYCLING. + + This method should not attempt to release any references held by the + caller. The caller will invoke the put_object() method as appropriate. + + + (*) Release object reference [mandatory]: + + void (*put_object)(struct fscache_object *object) + + This method is used to discard a reference to an object. The object may + be freed when all the references to it are released. + + + (*) Synchronise a cache [mandatory]: + + void (*sync)(struct fscache_cache *cache) + + This is called to ask the backend to synchronise a cache with its backing + device. + + + (*) Dissociate a cache [mandatory]: + + void (*dissociate_pages)(struct fscache_cache *cache) + + This is called to ask a cache to perform any page dissociations as part of + cache withdrawal. + + + (*) Notification that the attributes on a netfs file changed [mandatory]: + + int (*attr_changed)(struct fscache_object *object); + + This is called to indicate to the cache that certain attributes on a netfs + file have changed (for example the maximum size a file may reach). The + cache can read these from the netfs by calling the cookie's get_attr() + method. + + The cache may use the file size information to reserve space on the cache. + It should also call fscache_set_store_limit() to indicate to FS-Cache the + highest byte it's willing to store for an object. + + This method may return -ve if an error occurred or the cache object cannot + be expanded. In such a case, the object will be withdrawn from service. + + This operation is run asynchronously from FS-Cache's thread pool, and + storage and retrieval operations from the netfs are excluded during the + execution of this operation. + + + (*) Reserve cache space for an object's data [optional]: + + int (*reserve_space)(struct fscache_object *object, loff_t size); + + This is called to request that cache space be reserved to hold the data + for an object and the metadata used to track it. Zero size should be + taken as request to cancel a reservation. + + This should return 0 if successful, -ENOSPC if there isn't enough space + available, or -ENOMEM or -EIO on other errors. + + The reservation may exceed the current size of the object, thus permitting + future expansion. If the amount of space consumed by an object would + exceed the reservation, it's permitted to refuse requests to allocate + pages, but not required. An object may be pruned down to its reservation + size if larger than that already. + + + (*) Request page be read from cache [mandatory]: + + int (*read_or_alloc_page)(struct fscache_retrieval *op, + struct page *page, + gfp_t gfp) + + This is called to attempt to read a netfs page from the cache, or to + reserve a backing block if not. FS-Cache will have done as much checking + as it can before calling, but most of the work belongs to the backend. + + If there's no page in the cache, then -ENODATA should be returned if the + backend managed to reserve a backing block; -ENOBUFS or -ENOMEM if it + didn't. + + If there is suitable data in the cache, then a read operation should be + queued and 0 returned. When the read finishes, fscache_end_io() should be + called. + + The fscache_mark_pages_cached() should be called for the page if any cache + metadata is retained. This will indicate to the netfs that the page needs + explicit uncaching. This operation takes a pagevec, thus allowing several + pages to be marked at once. + + The retrieval record pointed to by op should be retained for each page + queued and released when I/O on the page has been formally ended. + fscache_get/put_retrieval() are available for this purpose. + + The retrieval record may be used to get CPU time via the FS-Cache thread + pool. If this is desired, the op->op.processor should be set to point to + the appropriate processing routine, and fscache_enqueue_retrieval() should + be called at an appropriate point to request CPU time. For instance, the + retrieval routine could be enqueued upon the completion of a disk read. + The to_do field in the retrieval record is provided to aid in this. + + If an I/O error occurs, fscache_io_error() should be called and -ENOBUFS + returned if possible or fscache_end_io() called with a suitable error + code.. + + + (*) Request pages be read from cache [mandatory]: + + int (*read_or_alloc_pages)(struct fscache_retrieval *op, + struct list_head *pages, + unsigned *nr_pages, + gfp_t gfp) + + This is like the read_or_alloc_page() method, except it is handed a list + of pages instead of one page. Any pages on which a read operation is + started must be added to the page cache for the specified mapping and also + to the LRU. Such pages must also be removed from the pages list and + *nr_pages decremented per page. + + If there was an error such as -ENOMEM, then that should be returned; else + if one or more pages couldn't be read or allocated, then -ENOBUFS should + be returned; else if one or more pages couldn't be read, then -ENODATA + should be returned. If all the pages are dispatched then 0 should be + returned. + + + (*) Request page be allocated in the cache [mandatory]: + + int (*allocate_page)(struct fscache_retrieval *op, + struct page *page, + gfp_t gfp) + + This is like the read_or_alloc_page() method, except that it shouldn't + read from the cache, even if there's data there that could be retrieved. + It should, however, set up any internal metadata required such that + the write_page() method can write to the cache. + + If there's no backing block available, then -ENOBUFS should be returned + (or -ENOMEM if there were other problems). If a block is successfully + allocated, then the netfs page should be marked and 0 returned. + + + (*) Request pages be allocated in the cache [mandatory]: + + int (*allocate_pages)(struct fscache_retrieval *op, + struct list_head *pages, + unsigned *nr_pages, + gfp_t gfp) + + This is an multiple page version of the allocate_page() method. pages and + nr_pages should be treated as for the read_or_alloc_pages() method. + + + (*) Request page be written to cache [mandatory]: + + int (*write_page)(struct fscache_storage *op, + struct page *page); + + This is called to write from a page on which there was a previously + successful read_or_alloc_page() call or similar. FS-Cache filters out + pages that don't have mappings. + + This method is called asynchronously from the FS-Cache thread pool. It is + not required to actually store anything, provided -ENODATA is then + returned to the next read of this page. + + If an error occurred, then a negative error code should be returned, + otherwise zero should be returned. FS-Cache will take appropriate action + in response to an error, such as withdrawing this object. + + If this method returns success then FS-Cache will inform the netfs + appropriately. + + + (*) Discard retained per-page metadata [mandatory]: + + void (*uncache_page)(struct fscache_object *object, struct page *page) + + This is called when a netfs page is being evicted from the pagecache. The + cache backend should tear down any internal representation or tracking it + maintains for this page. + + +================== +FS-CACHE UTILITIES +================== + +FS-Cache provides some utilities that a cache backend may make use of: + + (*) Note occurrence of an I/O error in a cache: + + void fscache_io_error(struct fscache_cache *cache) + + This tells FS-Cache that an I/O error occurred in the cache. After this + has been called, only resource dissociation operations (object and page + release) will be passed from the netfs to the cache backend for the + specified cache. + + This does not actually withdraw the cache. That must be done separately. + + + (*) Invoke the retrieval I/O completion function: + + void fscache_end_io(struct fscache_retrieval *op, struct page *page, + int error); + + This is called to note the end of an attempt to retrieve a page. The + error value should be 0 if successful and an error otherwise. + + + (*) Set highest store limit: + + void fscache_set_store_limit(struct fscache_object *object, + loff_t i_size); + + This sets the limit FS-Cache imposes on the highest byte it's willing to + try and store for a netfs. Any page over this limit is automatically + rejected by fscache_read_alloc_page() and co with -ENOBUFS. + + + (*) Mark pages as being cached: + + void fscache_mark_pages_cached(struct fscache_retrieval *op, + struct pagevec *pagevec); + + This marks a set of pages as being cached. After this has been called, + the netfs must call fscache_uncache_page() to unmark the pages. + + + (*) Perform coherency check on an object: + + enum fscache_checkaux fscache_check_aux(struct fscache_object *object, + const void *data, + uint16_t datalen); + + This asks the netfs to perform a coherency check on an object that has + just been looked up. The cookie attached to the object will determine the + netfs to use. data and datalen should specify where the auxiliary data + retrieved from the cache can be found. + + One of three values will be returned: + + (*) FSCACHE_CHECKAUX_OKAY + + The coherency data indicates the object is valid as is. + + (*) FSCACHE_CHECKAUX_NEEDS_UPDATE + + The coherency data needs updating, but otherwise the object is + valid. + + (*) FSCACHE_CHECKAUX_OBSOLETE + + The coherency data indicates that the object is obsolete and should + be discarded. + + + (*) Initialise a freshly allocated object: + + void fscache_object_init(struct fscache_object *object); + + This initialises all the fields in an object representation. + + + (*) Indicate the destruction of an object: + + void fscache_object_destroyed(struct fscache_cache *cache); + + This must be called to inform FS-Cache that an object that belonged to a + cache has been destroyed and deallocated. This will allow continuation + of the cache withdrawal process when it is stopped pending destruction of + all the objects. + + + (*) Indicate negative lookup on an object: + + void fscache_object_lookup_negative(struct fscache_object *object); + + This is called to indicate to FS-Cache that a lookup process for an object + found a negative result. + + This changes the state of an object to permit reads pending on lookup + completion to go off and start fetching data from the netfs server as it's + known at this point that there can't be any data in the cache. + + This may be called multiple times on an object. Only the first call is + significant - all subsequent calls are ignored. + + + (*) Indicate an object has been obtained: + + void fscache_obtained_object(struct fscache_object *object); + + This is called to indicate to FS-Cache that a lookup process for an object + produced a positive result, or that an object was created. This should + only be called once for any particular object. + + This changes the state of an object to indicate: + + (1) if no call to fscache_object_lookup_negative() has been made on + this object, that there may be data available, and that reads can + now go and look for it; and + + (2) that writes may now proceed against this object. + + + (*) Indicate that object lookup failed: + + void fscache_object_lookup_error(struct fscache_object *object); + + This marks an object as having encountered a fatal error (usually EIO) + and causes it to move into a state whereby it will be withdrawn as soon + as possible. + + + (*) Get and release references on a retrieval record: + + void fscache_get_retrieval(struct fscache_retrieval *op); + void fscache_put_retrieval(struct fscache_retrieval *op); + + These two functions are used to retain a retrieval record whilst doing + asynchronous data retrieval and block allocation. + + + (*) Enqueue a retrieval record for processing. + + void fscache_enqueue_retrieval(struct fscache_retrieval *op); + + This enqueues a retrieval record for processing by the FS-Cache thread + pool. One of the threads in the pool will invoke the retrieval record's + op->op.processor callback function. This function may be called from + within the callback function. + + + (*) List of object state names: + + const char *fscache_object_states[]; + + For debugging purposes, this may be used to turn the state that an object + is in into a text string for display purposes. diff --git a/include/linux/fscache-cache.h b/include/linux/fscache-cache.h new file mode 100644 index 00000000000..b2a9a484c4c --- /dev/null +++ b/include/linux/fscache-cache.h @@ -0,0 +1,509 @@ +/* General filesystem caching backing cache interface + * + * Copyright (C) 2004-2007 Red Hat, Inc. All Rights Reserved. + * Written by David Howells (dhowells@redhat.com) + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License + * as published by the Free Software Foundation; either version + * 2 of the License, or (at your option) any later version. + * + * NOTE!!! See: + * + * Documentation/filesystems/caching/backend-api.txt + * + * for a description of the cache backend interface declared here. + */ + +#ifndef _LINUX_FSCACHE_CACHE_H +#define _LINUX_FSCACHE_CACHE_H + +#include <linux/fscache.h> +#include <linux/sched.h> +#include <linux/slow-work.h> + +#define NR_MAXCACHES BITS_PER_LONG + +struct fscache_cache; +struct fscache_cache_ops; +struct fscache_object; +struct fscache_operation; + +#ifdef CONFIG_FSCACHE_PROC +extern struct proc_dir_entry *proc_fscache; +#endif + +/* + * cache tag definition + */ +struct fscache_cache_tag { + struct list_head link; + struct fscache_cache *cache; /* cache referred to by this tag */ + unsigned long flags; +#define FSCACHE_TAG_RESERVED 0 /* T if tag is reserved for a cache */ + atomic_t usage; + char name[0]; /* tag name */ +}; + +/* + * cache definition + */ +struct fscache_cache { + const struct fscache_cache_ops *ops; + struct fscache_cache_tag *tag; /* tag representing this cache */ + struct kobject *kobj; /* system representation of this cache */ + struct list_head link; /* link in list of caches */ + size_t max_index_size; /* maximum size of index data */ + char identifier[36]; /* cache label */ + + /* node management */ + struct work_struct op_gc; /* operation garbage collector */ + struct list_head object_list; /* list of data/index objects */ + struct list_head op_gc_list; /* list of ops to be deleted */ + spinlock_t object_list_lock; + spinlock_t op_gc_list_lock; + atomic_t object_count; /* no. of live objects in this cache */ + struct fscache_object *fsdef; /* object for the fsdef index */ + unsigned long flags; +#define FSCACHE_IOERROR 0 /* cache stopped on I/O error */ +#define FSCACHE_CACHE_WITHDRAWN 1 /* cache has been withdrawn */ +}; + +extern wait_queue_head_t fscache_cache_cleared_wq; + +/* + * operation to be applied to a cache object + * - retrieval initiation operations are done in the context of the process + * that issued them, and not in an async thread pool + */ +typedef void (*fscache_operation_release_t)(struct fscache_operation *op); +typedef void (*fscache_operation_processor_t)(struct fscache_operation *op); + +struct fscache_operation { + union { + struct work_struct fast_work; /* record for fast ops */ + struct slow_work slow_work; /* record for (very) slow ops */ + }; + struct list_head pend_link; /* link in object->pending_ops */ + struct fscache_object *object; /* object to be operated upon */ + + unsigned long flags; +#define FSCACHE_OP_TYPE 0x000f /* operation type */ +#define FSCACHE_OP_FAST 0x0001 /* - fast op, processor may not sleep for disk */ +#define FSCACHE_OP_SLOW 0x0002 /* - (very) slow op, processor may sleep for disk */ +#define FSCACHE_OP_MYTHREAD 0x0003 /* - processing is done be issuing thread, not pool */ +#define FSCACHE_OP_WAITING 4 /* cleared when op is woken */ +#define FSCACHE_OP_EXCLUSIVE 5 /* exclusive op, other ops must wait */ +#define FSCACHE_OP_DEAD 6 /* op is now dead */ + + atomic_t usage; + unsigned debug_id; /* debugging ID */ + + /* operation processor callback + * - can be NULL if FSCACHE_OP_WAITING is going to be used to perform + * the op in a non-pool thread */ + fscache_operation_processor_t processor; + + /* operation releaser */ + fscache_operation_release_t release; +}; + +extern atomic_t fscache_op_debug_id; +extern const struct slow_work_ops fscache_op_slow_work_ops; + +extern void fscache_enqueue_operation(struct fscache_operation *); +extern void fscache_put_operation(struct fscache_operation *); + +/** + * fscache_operation_init - Do basic initialisation of an operation + * @op: The operation to initialise + * @release: The release function to assign + * + * Do basic initialisation of an operation. The caller must still set flags, + * object, either fast_work or slow_work if necessary, and processor if needed. + */ +static inline void fscache_operation_init(struct fscache_operation *op, + fscache_operation_release_t release) +{ + atomic_set(&op->usage, 1); + op->debug_id = atomic_inc_return(&fscache_op_debug_id); + op->release = release; + INIT_LIST_HEAD(&op->pend_link); +} + +/** + * fscache_operation_init_slow - Do additional initialisation of a slow op + * @op: The operation to initialise + * @processor: The processor function to assign + * + * Do additional initialisation of an operation as required for slow work. + */ +static inline +void fscache_operation_init_slow(struct fscache_operation *op, + fscache_operation_processor_t processor) +{ + op->processor = processor; + slow_work_init(&op->slow_work, &fscache_op_slow_work_ops); +} + +/* + * data read operation + */ +struct fscache_retrieval { + struct fscache_operation op; + struct address_space *mapping; /* netfs pages */ + fscache_rw_complete_t end_io_func; /* function to call on I/O completion */ + void *context; /* netfs read context (pinned) */ + struct list_head to_do; /* list of things to be done by the backend */ + unsigned long start_time; /* time at which retrieval started */ +}; + +typedef int (*fscache_page_retrieval_func_t)(struct fscache_retrieval *op, + struct page *page, + gfp_t gfp); + +typedef int (*fscache_pages_retrieval_func_t)(struct fscache_retrieval *op, + struct list_head *pages, + unsigned *nr_pages, + gfp_t gfp); + +/** + * fscache_get_retrieval - Get an extra reference on a retrieval operation + * @op: The retrieval operation to get a reference on + * + * Get an extra reference on a retrieval operation. + */ +static inline +struct fscache_retrieval *fscache_get_retrieval(struct fscache_retrieval *op) +{ + atomic_inc(&op->op.usage); + return op; +} + +/** + * fscache_enqueue_retrieval - Enqueue a retrieval operation for processing + * @op: The retrieval operation affected + * + * Enqueue a retrieval operation for processing by the FS-Cache thread pool. + */ +static inline void fscache_enqueue_retrieval(struct fscache_retrieval *op) +{ + fscache_enqueue_operation(&op->op); +} + +/** + * fscache_put_retrieval - Drop a reference to a retrieval operation + * @op: The retrieval operation affected + * + * Drop a reference to a retrieval operation. + */ +static inline void fscache_put_retrieval(struct fscache_retrieval *op) +{ + fscache_put_operation(&op->op); +} + +/* + * cached page storage work item + * - used to do three things: + * - batch writes to the cache + * - do cache writes asynchronously + * - defer writes until cache object lookup completion + */ +struct fscache_storage { + struct fscache_operation op; + pgoff_t store_limit; /* don't write more than this */ +}; + +/* + * cache operations + */ +struct fscache_cache_ops { + /* name of cache provider */ + const char *name; + + /* allocate an object record for a cookie */ + struct fscache_object *(*alloc_object)(struct fscache_cache *cache, + struct fscache_cookie *cookie); + + /* look up the object for a cookie */ + void (*lookup_object)(struct fscache_object *object); + + /* finished looking up */ + void (*lookup_complete)(struct fscache_object *object); + + /* increment the usage count on this object (may fail if unmounting) */ + struct fscache_object *(*grab_object)(struct fscache_object *object); + + /* pin an object in the cache */ + int (*pin_object)(struct fscache_object *object); + + /* unpin an object in the cache */ + void (*unpin_object)(struct fscache_object *object); + + /* store the updated auxilliary data on an object */ + void (*update_object)(struct fscache_object *object); + + /* discard the resources pinned by an object and effect retirement if + * necessary */ + void (*drop_object)(struct fscache_object *object); + + /* dispose of a reference to an object */ + void (*put_object)(struct fscache_object *object); + + /* sync a cache */ + void (*sync_cache)(struct fscache_cache *cache); + + /* notification that the attributes of a non-index object (such as + * i_size) have changed */ + int (*attr_changed)(struct fscache_object *object); + + /* reserve space for an object's data and associated metadata */ + int (*reserve_space)(struct fscache_object *object, loff_t i_size); + + /* request a backing block for a page be read or allocated in the + * cache */ + fscache_page_retrieval_func_t read_or_alloc_page; + + /* request backing blocks for a list of pages be read or allocated in + * the cache */ + fscache_pages_retrieval_func_t read_or_alloc_pages; + + /* request a backing block for a page be allocated in the cache so that + * it can be written directly */ + fscache_page_retrieval_func_t allocate_page; + + /* request backing blocks for pages be allocated in the cache so that + * they can be written directly */ + fscache_pages_retrieval_func_t allocate_pages; + + /* write a page to its backing block in the cache */ + int (*write_page)(struct fscache_storage *op, struct page *page); + + /* detach backing block from a page (optional) + * - must release the cookie lock before returning + * - may sleep + */ + void (*uncache_page)(struct fscache_object *object, + struct page *page); + + /* dissociate a cache from all the pages it was backing */ + void (*dissociate_pages)(struct fscache_cache *cache); +}; + +/* + * data file or index object cookie + * - a file will only appear in one cache + * - a request to cache a file may or may not be honoured, subject to + * constraints such as disk space + * - indices are created on disk just-in-time + */ +struct fscache_cookie { + atomic_t usage; /* number of users of this cookie */ + atomic_t n_children; /* number of children of this cookie */ + spinlock_t lock; + struct hlist_head backing_objects; /* object(s) backing this file/index */ + const struct fscache_cookie_def *def; /* definition */ + struct fscache_cookie *parent; /* parent of this entry */ + void *netfs_data; /* back pointer to netfs */ + struct radix_tree_root stores; /* pages to be stored on this cookie */ +#define FSCACHE_COOKIE_PENDING_TAG 0 /* pages tag: pending write to cache */ + + unsigned long flags; +#define FSCACHE_COOKIE_LOOKING_UP 0 /* T if non-index cookie being looked up still */ +#define FSCACHE_COOKIE_CREATING 1 /* T if non-index object being created still */ +#define FSCACHE_COOKIE_NO_DATA_YET 2 /* T if new object with no cached data yet */ +#define FSCACHE_COOKIE_PENDING_FILL 3 /* T if pending initial fill on object */ +#define FSCACHE_COOKIE_FILLING 4 /* T if filling object incrementally */ +#define FSCACHE_COOKIE_UNAVAILABLE 5 /* T if cookie is unavailable (error, etc) */ +}; + +extern struct fscache_cookie fscache_fsdef_index; + +/* + * on-disk cache file or index handle + */ +struct fscache_object { + enum fscache_object_state { + FSCACHE_OBJECT_INIT, /* object in initial unbound state */ + FSCACHE_OBJECT_LOOKING_UP, /* looking up object */ + FSCACHE_OBJECT_CREATING, /* creating object */ + + /* active states */ + FSCACHE_OBJECT_AVAILABLE, /* cleaning up object after creation */ + FSCACHE_OBJECT_ACTIVE, /* object is usable */ + FSCACHE_OBJECT_UPDATING, /* object is updating */ + + /* terminal states */ + FSCACHE_OBJECT_DYING, /* object waiting for accessors to finish */ + FSCACHE_OBJECT_LC_DYING, /* object cleaning up after lookup/create */ + FSCACHE_OBJECT_ABORT_INIT, /* abort the init state */ + FSCACHE_OBJECT_RELEASING, /* releasing object */ + FSCACHE_OBJECT_RECYCLING, /* retiring object */ + FSCACHE_OBJECT_WITHDRAWING, /* withdrawing object */ + FSCACHE_OBJECT_DEAD, /* object is now dead */ + } state; + + int debug_id; /* debugging ID */ + int n_children; /* number of child objects */ + int n_ops; /* number of ops outstanding on object */ + int n_obj_ops; /* number of object ops outstanding on object */ + int n_in_progress; /* number of ops in progress */ + int n_exclusive; /* number of exclusive ops queued */ + spinlock_t lock; /* state and operations lock */ + + unsigned long lookup_jif; /* time at which lookup started */ + unsigned long event_mask; /* events this object is interested in */ + unsigned long events; /* events to be processed by this object + * (order is important - using fls) */ +#define FSCACHE_OBJECT_EV_REQUEUE 0 /* T if object should be requeued */ +#define FSCACHE_OBJECT_EV_UPDATE 1 /* T if object should be updated */ +#define FSCACHE_OBJECT_EV_CLEARED 2 /* T if accessors all gone */ +#define FSCACHE_OBJECT_EV_ERROR 3 /* T if fatal error occurred during processing */ +#define FSCACHE_OBJECT_EV_RELEASE 4 /* T if netfs requested object release */ +#define FSCACHE_OBJECT_EV_RETIRE 5 /* T if netfs requested object retirement */ +#define FSCACHE_OBJECT_EV_WITHDRAW 6 /* T if cache requested object withdrawal */ + + unsigned long flags; +#define FSCACHE_OBJECT_LOCK 0 /* T if object is busy being processed */ +#define FSCACHE_OBJECT_PENDING_WRITE 1 /* T if object has pending write */ +#define FSCACHE_OBJECT_WAITING 2 /* T if object is waiting on its parent */ + + struct list_head cache_link; /* link in cache->object_list */ + struct hlist_node cookie_link; /* link in cookie->backing_objects */ + struct fscache_cache *cache; /* cache that supplied this object */ + struct fscache_cookie *cookie; /* netfs's file/index object */ + struct fscache_object *parent; /* parent object */ + struct slow_work work; /* attention scheduling record */ + struct list_head dependents; /* FIFO of dependent objects */ + struct list_head dep_link; /* link in parent's dependents list */ + struct list_head pending_ops; /* unstarted operations on this object */ + pgoff_t store_limit; /* current storage limit */ +}; + +extern const char *fscache_object_states[]; + +#define fscache_object_is_active(obj) \ + (!test_bit(FSCACHE_IOERROR, &(obj)->cache->flags) && \ + (obj)->state >= FSCACHE_OBJECT_AVAILABLE && \ + (obj)->state < FSCACHE_OBJECT_DYING) + +extern const struct slow_work_ops fscache_object_slow_work_ops; + +/** + * fscache_object_init - Initialise a cache object description + * @object: Object description + * + * Initialise a cache object description to its basic values. + * + * See Documentation/filesystems/caching/backend-api.txt for a complete + * description. + */ +static inline +void fscache_object_init(struct fscache_object *object, + struct fscache_cookie *cookie, + struct fscache_cache *cache) +{ + atomic_inc(&cache->object_count); + + object->state = FSCACHE_OBJECT_INIT; + spin_lock_init(&object->lock); + INIT_LIST_HEAD(&object->cache_link); + INIT_HLIST_NODE(&object->cookie_link); + vslow_work_init(&object->work, &fscache_object_slow_work_ops); + INIT_LIST_HEAD(&object->dependents); + INIT_LIST_HEAD(&object->dep_link); + INIT_LIST_HEAD(&object->pending_ops); + object->n_children = 0; + object->n_ops = object->n_in_progress = object->n_exclusive = 0; + object->events = object->event_mask = 0; + object->flags = 0; + object->store_limit = 0; + object->cache = cache; + object->cookie = cookie; + object->parent = NULL; +} + +extern void fscache_object_lookup_negative(struct fscache_object *object); +extern void fscache_obtained_object(struct fscache_object *object); + +/** + * fscache_object_destroyed - Note destruction of an object in a cache + * @cache: The cache from which the object came + * + * Note the destruction and deallocation of an object record in a cache. + */ +static inline void fscache_object_destroyed(struct fscache_cache *cache) +{ + if (atomic_dec_and_test(&cache->object_count)) + wake_up_all(&fscache_cache_cleared_wq); +} + +/** + * fscache_object_lookup_error - Note an object encountered an error + * @object: The object on which the error was encountered + * + * Note that an object encountered a fatal error (usually an I/O error) and + * that it should be withdrawn as soon as possible. + */ +static inline void fscache_object_lookup_error(struct fscache_object *object) +{ + set_bit(FSCACHE_OBJECT_EV_ERROR, &object->events); +} + +/** + * fscache_set_store_limit - Set the maximum size to be stored in an object + * @object: The object to set the maximum on + * @i_size: The limit to set in bytes + * + * Set the maximum size an object is permitted to reach, implying the highest + * byte that may be written. Intended to be called by the attr_changed() op. + * + * See Documentation/filesystems/caching/backend-api.txt for a complete + * description. + */ +static inline +void fscache_set_store_limit(struct fscache_object *object, loff_t i_size) +{ + object->store_limit = i_size >> PAGE_SHIFT; + if (i_size & ~PAGE_MASK) + object->store_limit++; +} + +/** + * fscache_end_io - End a retrieval operation on a page + * @op: The FS-Cache operation covering the retrieval + * @page: The page that was to be fetched + * @error: The error code (0 if successful) + * + * Note the end of an operation to retrieve a page, as covered by a particular + * operation record. + */ +static inline void fscache_end_io(struct fscache_retrieval *op, + struct page *page, int error) +{ + op->end_io_func(page, op->context, error); +} + +/* + * out-of-line cache backend functions + */ +extern void fscache_init_cache(struct fscache_cache *cache, + const struct fscache_cache_ops *ops, + const char *idfmt, + ...) __attribute__ ((format (printf, 3, 4))); + +extern int fscache_add_cache(struct fscache_cache *cache, + struct fscache_object *fsdef, + const char *tagname); +extern void fscache_withdraw_cache(struct fscache_cache *cache); + +extern void fscache_io_error(struct fscache_cache *cache); + +extern void fscache_mark_pages_cached(struct fscache_retrieval *op, + struct pagevec *pagevec); + +extern enum fscache_checkaux fscache_check_aux(struct fscache_object *object, + const void *data, + uint16_t datalen); + +#endif /* _LINUX_FSCACHE_CACHE_H */ |