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    Subject[PATCH 08/43] FS-Cache: Add the FS-Cache cache backend API and documentation [ver #46]
    Date
    Add the API for a generic facility (FS-Cache) by which caches may declare them
    selves open for business, and may obtain work to be done from network
    filesystems. The header file is included by:

    #include <linux/fscache-cache.h>

    Documentation for the API is also added to:

    Documentation/filesystems/caching/backend-api.txt

    This API is not usable without the implementation of the utility functions
    which will be added in further patches.

    Signed-off-by: David Howells <dhowells@redhat.com>
    Acked-by: Steve Dickson <steved@redhat.com>
    Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com>
    ---

    Documentation/filesystems/caching/backend-api.txt | 664 +++++++++++++++++++++
    include/linux/fscache-cache.h | 508 ++++++++++++++++
    2 files changed, 1172 insertions(+), 0 deletions(-)
    create mode 100644 Documentation/filesystems/caching/backend-api.txt
    create mode 100644 include/linux/fscache-cache.h


    diff --git a/Documentation/filesystems/caching/backend-api.txt b/Documentation/filesystems/caching/backend-api.txt
    new file mode 100644
    index 0000000..1772305
    --- /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 0000000..a31f4c1
    --- /dev/null
    +++ b/include/linux/fscache-cache.h
    @@ -0,0 +1,508 @@
    +/* 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 */
    + 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 */
    + struct radix_tree_root stores; /* data to be stored */
    + 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);
    + INIT_RADIX_TREE(&object->stores, GFP_NOFS);
    + 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 */


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