703 lines
24 KiB
Text
703 lines
24 KiB
Text
==========================
|
|
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A cache can be withdrawn from the system by calling this function with a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.
|
|
|
|
|
|
========================
|
|
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.
|
|
|
|
|
|
(*) Check coherency state of an object [mandatory]:
|
|
|
|
int (*check_consistency)(struct fscache_object *object)
|
|
|
|
This method is called to have the cache check the saved auxiliary data of
|
|
the object against the netfs's idea of the state. 0 should be returned
|
|
if they're consistent and -ESTALE otherwise. -ENOMEM and -ERESTARTSYS
|
|
may also be returned.
|
|
|
|
(*) 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().
|
|
|
|
|
|
(*) Invalidate data object [mandatory]:
|
|
|
|
int (*invalidate_object)(struct fscache_operation *op)
|
|
|
|
This is called to invalidate a data object (as pointed to by op->object).
|
|
All the data stored for this object should be discarded and an
|
|
attr_changed operation should be performed. The caller will follow up
|
|
with an object update operation.
|
|
|
|
fscache_op_complete() must be called on op before returning.
|
|
|
|
|
|
(*) 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.
|
|
|
|
fscache_put_retrieval() should be called after a page or pages are dealt
|
|
with. This will complete the operation when all pages are dealt with.
|
|
|
|
|
|
(*) 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.
|
|
|
|
|
|
(*) Record that one or more pages being retrieved or allocated have been dealt
|
|
with:
|
|
|
|
void fscache_retrieval_complete(struct fscache_retrieval *op,
|
|
int n_pages);
|
|
|
|
This is called to record the fact that one or more pages have been dealt
|
|
with and are no longer the concern of this operation. When the number of
|
|
pages remaining in the operation reaches 0, the operation will be
|
|
completed.
|
|
|
|
|
|
(*) Record operation completion:
|
|
|
|
void fscache_op_complete(struct fscache_operation *op);
|
|
|
|
This is called to record the completion of an operation. This deducts
|
|
this operation from the parent object's run state, potentially permitting
|
|
one or more pending operations to start running.
|
|
|
|
|
|
(*) 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.
|