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+			  ==========================
+			  General Filesystem Caching
+			  ==========================
+
+========
+OVERVIEW
+========
+
+This facility is a general purpose cache for network filesystems, though it
+could be used for caching other things such as ISO9660 filesystems too.
+
+FS-Cache mediates between cache backends (such as CacheFS) and network
+filesystems:
+
+	+---------+
+	|         |                        +--------------+
+	|   NFS   |--+                     |              |
+	|         |  |                 +-->|   CacheFS    |
+	+---------+  |   +----------+  |   |  /dev/hda5   |
+	             |   |          |  |   +--------------+
+	+---------+  +-->|          |  |
+	|         |      |          |--+
+	|   AFS   |----->| FS-Cache |
+	|         |      |          |--+
+	+---------+  +-->|          |  |
+	             |   |          |  |   +--------------+
+	+---------+  |   +----------+  |   |              |
+	|         |  |                 +-->|  CacheFiles  |
+	|  ISOFS  |--+                     |  /var/cache  |
+	|         |                        +--------------+
+	+---------+
+
+Or to look at it another way, FS-Cache is a module that provides a caching
+facility to a network filesystem such that the cache is transparent to the
+user:
+
+	+---------+
+	|         |
+	| Server  |
+	|         |
+	+---------+
+	     |                  NETWORK
+	~~~~~|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+	     |
+	     |           +----------+
+	     V           |          |
+	+---------+      |          |
+	|         |      |          |
+	|   NFS   |----->| FS-Cache |
+	|         |      |          |--+
+	+---------+      |          |  |   +--------------+   +--------------+
+	     |           |          |  |   |              |   |              |
+	     V           +----------+  +-->|  CacheFiles  |-->|  Ext3        |
+	+---------+                        |  /var/cache  |   |  /dev/sda6   |
+	|         |                        +--------------+   +--------------+
+	|   VFS   |                                ^                     ^
+	|         |                                |                     |
+	+---------+                                +--------------+      |
+	     |                  KERNEL SPACE                      |      |
+	~~~~~|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~|~~~~~~|~~~~
+	     |                  USER SPACE                        |      |
+	     V                                                    |      |
+	+---------+                                           +--------------+
+	|         |                                           |              |
+	| Process |                                           | cachefilesd  |
+	|         |                                           |              |
+	+---------+                                           +--------------+
+
+
+FS-Cache does not follow the idea of completely loading every netfs file
+opened in its entirety into a cache before permitting it to be accessed and
+then serving the pages out of that cache rather than the netfs inode because:
+
+ (1) It must be practical to operate without a cache.
+
+ (2) The size of any accessible file must not be limited to the size of the
+     cache.
+
+ (3) The combined size of all opened files (this includes mapped libraries)
+     must not be limited to the size of the cache.
+
+ (4) The user should not be forced to download an entire file just to do a
+     one-off access of a small portion of it (such as might be done with the
+     "file" program).
+
+It instead serves the cache out in PAGE_SIZE chunks as and when requested by
+the netfs('s) using it.
+
+
+FS-Cache provides the following facilities:
+
+ (1) More than one cache can be used at once.  Caches can be selected
+     explicitly by use of tags.
+
+ (2) Caches can be added / removed at any time.
+
+ (3) The netfs is provided with an interface that allows either party to
+     withdraw caching facilities from a file (required for (2)).
+
+ (4) The interface to the netfs returns as few errors as possible, preferring
+     rather to let the netfs remain oblivious.
+
+ (5) Cookies are used to represent indices, files and other objects to the
+     netfs.  The simplest cookie is just a NULL pointer - indicating nothing
+     cached there.
+
+ (6) The netfs is allowed to propose - dynamically - any index hierarchy it
+     desires, though it must be aware that the index search function is
+     recursive, stack space is limited, and indices can only be children of
+     indices.
+
+ (7) Data I/O is done direct to and from the netfs's pages.  The netfs
+     indicates that page A is at index B of the data-file represented by cookie
+     C, and that it should be read or written.  The cache backend may or may
+     not start I/O on that page, but if it does, a netfs callback will be
+     invoked to indicate completion.  The I/O may be either synchronous or
+     asynchronous.
+
+ (8) Cookies can be "retired" upon release.  At this point FS-Cache will mark
+     them as obsolete and the index hierarchy rooted at that point will get
+     recycled.
+
+ (9) The netfs provides a "match" function for index searches.  In addition to
+     saying whether a match was made or not, this can also specify that an
+     entry should be updated or deleted.
+
+(10) As much as possible is done asynchronously.
+
+
+FS-Cache maintains a virtual indexing tree in which all indices, files, objects
+and pages are kept.  Bits of this tree may actually reside in one or more
+caches.
+
+                                           FSDEF
+                                             |
+                        +------------------------------------+
+                        |                                    |
+                       NFS                                  AFS
+                        |                                    |
+           +--------------------------+                +-----------+
+           |                          |                |           |
+        homedir                     mirror          afs.org   redhat.com
+           |                          |                            |
+     +------------+           +---------------+              +----------+
+     |            |           |               |              |          |
+   00001        00002       00007           00125        vol00001   vol00002
+     |            |           |               |                         |
+ +---+---+     +-----+      +---+      +------+------+            +-----+----+
+ |   |   |     |     |      |   |      |      |      |            |     |    |
+PG0 PG1 PG2   PG0  XATTR   PG0 PG1   DIRENT DIRENT DIRENT        R/W   R/O  Bak
+                     |                                            |
+                    PG0                                       +-------+
+                                                              |       |
+                                                            00001   00003
+                                                              |
+                                                          +---+---+
+                                                          |   |   |
+                                                         PG0 PG1 PG2
+
+In the example above, you can see two netfs's being backed: NFS and AFS.  These
+have different index hierarchies:
+
+ (*) The NFS primary index contains per-server indices.  Each server index is
+     indexed by NFS file handles to get data file objects.  Each data file
+     objects can have an array of pages, but may also have further child
+     objects, such as extended attributes and directory entries.  Extended
+     attribute objects themselves have page-array contents.
+
+ (*) The AFS primary index contains per-cell indices.  Each cell index contains
+     per-logical-volume indices.  Each of volume index contains up to three
+     indices for the read-write, read-only and backup mirrors of those volumes.
+     Each of these contains vnode data file objects, each of which contains an
+     array of pages.
+
+The very top index is the FS-Cache master index in which individual netfs's
+have entries.
+
+Any index object may reside in more than one cache, provided it only has index
+children.  Any index with non-index object children will be assumed to only
+reside in one cache.
+
+
+The netfs API to FS-Cache can be found in:
+
+	Documentation/filesystems/caching/netfs-api.txt
+
+The cache backend API to FS-Cache can be found in:
+
+	Documentation/filesystems/caching/backend-api.txt
+
+A description of the internal representations and object state machine can be
+found in:
+
+	Documentation/filesystems/caching/object.txt
+
+
+=======================
+STATISTICAL INFORMATION
+=======================
+
+If FS-Cache is compiled with the following options enabled:
+
+	CONFIG_FSCACHE_STATS=y
+	CONFIG_FSCACHE_HISTOGRAM=y
+
+then it will gather certain statistics and display them through a number of
+proc files.
+
+ (*) /proc/fs/fscache/stats
+
+     This shows counts of a number of events that can happen in FS-Cache:
+
+	CLASS	EVENT	MEANING
+	=======	=======	=======================================================
+	Cookies	idx=N	Number of index cookies allocated
+		dat=N	Number of data storage cookies allocated
+		spc=N	Number of special cookies allocated
+	Objects	alc=N	Number of objects allocated
+		nal=N	Number of object allocation failures
+		avl=N	Number of objects that reached the available state
+		ded=N	Number of objects that reached the dead state
+	ChkAux	non=N	Number of objects that didn't have a coherency check
+		ok=N	Number of objects that passed a coherency check
+		upd=N	Number of objects that needed a coherency data update
+		obs=N	Number of objects that were declared obsolete
+	Pages	mrk=N	Number of pages marked as being cached
+		unc=N	Number of uncache page requests seen
+	Acquire	n=N	Number of acquire cookie requests seen
+		nul=N	Number of acq reqs given a NULL parent
+		noc=N	Number of acq reqs rejected due to no cache available
+		ok=N	Number of acq reqs succeeded
+		nbf=N	Number of acq reqs rejected due to error
+		oom=N	Number of acq reqs failed on ENOMEM
+	Lookups	n=N	Number of lookup calls made on cache backends
+		neg=N	Number of negative lookups made
+		pos=N	Number of positive lookups made
+		crt=N	Number of objects created by lookup
+		tmo=N	Number of lookups timed out and requeued
+	Updates	n=N	Number of update cookie requests seen
+		nul=N	Number of upd reqs given a NULL parent
+		run=N	Number of upd reqs granted CPU time
+	Relinqs	n=N	Number of relinquish cookie requests seen
+		nul=N	Number of rlq reqs given a NULL parent
+		wcr=N	Number of rlq reqs waited on completion of creation
+	AttrChg	n=N	Number of attribute changed requests seen
+		ok=N	Number of attr changed requests queued
+		nbf=N	Number of attr changed rejected -ENOBUFS
+		oom=N	Number of attr changed failed -ENOMEM
+		run=N	Number of attr changed ops given CPU time
+	Allocs	n=N	Number of allocation requests seen
+		ok=N	Number of successful alloc reqs
+		wt=N	Number of alloc reqs that waited on lookup completion
+		nbf=N	Number of alloc reqs rejected -ENOBUFS
+		int=N	Number of alloc reqs aborted -ERESTARTSYS
+		ops=N	Number of alloc reqs submitted
+		owt=N	Number of alloc reqs waited for CPU time
+		abt=N	Number of alloc reqs aborted due to object death
+	Retrvls	n=N	Number of retrieval (read) requests seen
+		ok=N	Number of successful retr reqs
+		wt=N	Number of retr reqs that waited on lookup completion
+		nod=N	Number of retr reqs returned -ENODATA
+		nbf=N	Number of retr reqs rejected -ENOBUFS
+		int=N	Number of retr reqs aborted -ERESTARTSYS
+		oom=N	Number of retr reqs failed -ENOMEM
+		ops=N	Number of retr reqs submitted
+		owt=N	Number of retr reqs waited for CPU time
+		abt=N	Number of retr reqs aborted due to object death
+	Stores	n=N	Number of storage (write) requests seen
+		ok=N	Number of successful store reqs
+		agn=N	Number of store reqs on a page already pending storage
+		nbf=N	Number of store reqs rejected -ENOBUFS
+		oom=N	Number of store reqs failed -ENOMEM
+		ops=N	Number of store reqs submitted
+		run=N	Number of store reqs granted CPU time
+		pgs=N	Number of pages given store req processing time
+		rxd=N	Number of store reqs deleted from tracking tree
+		olm=N	Number of store reqs over store limit
+	VmScan	nos=N	Number of release reqs against pages with no pending store
+		gon=N	Number of release reqs against pages stored by time lock granted
+		bsy=N	Number of release reqs ignored due to in-progress store
+		can=N	Number of page stores cancelled due to release req
+	Ops	pend=N	Number of times async ops added to pending queues
+		run=N	Number of times async ops given CPU time
+		enq=N	Number of times async ops queued for processing
+		can=N	Number of async ops cancelled
+		rej=N	Number of async ops rejected due to object lookup/create failure
+		dfr=N	Number of async ops queued for deferred release
+		rel=N	Number of async ops released
+		gc=N	Number of deferred-release async ops garbage collected
+	CacheOp	alo=N	Number of in-progress alloc_object() cache ops
+		luo=N	Number of in-progress lookup_object() cache ops
+		luc=N	Number of in-progress lookup_complete() cache ops
+		gro=N	Number of in-progress grab_object() cache ops
+		upo=N	Number of in-progress update_object() cache ops
+		dro=N	Number of in-progress drop_object() cache ops
+		pto=N	Number of in-progress put_object() cache ops
+		syn=N	Number of in-progress sync_cache() cache ops
+		atc=N	Number of in-progress attr_changed() cache ops
+		rap=N	Number of in-progress read_or_alloc_page() cache ops
+		ras=N	Number of in-progress read_or_alloc_pages() cache ops
+		alp=N	Number of in-progress allocate_page() cache ops
+		als=N	Number of in-progress allocate_pages() cache ops
+		wrp=N	Number of in-progress write_page() cache ops
+		ucp=N	Number of in-progress uncache_page() cache ops
+		dsp=N	Number of in-progress dissociate_pages() cache ops
+
+
+ (*) /proc/fs/fscache/histogram
+
+	cat /proc/fs/fscache/histogram
+	JIFS  SECS  OBJ INST  OP RUNS   OBJ RUNS  RETRV DLY RETRIEVLS
+	===== ===== ========= ========= ========= ========= =========
+
+     This shows the breakdown of the number of times each amount of time
+     between 0 jiffies and HZ-1 jiffies a variety of tasks took to run.  The
+     columns are as follows:
+
+	COLUMN		TIME MEASUREMENT
+	=======		=======================================================
+	OBJ INST	Length of time to instantiate an object
+	OP RUNS		Length of time a call to process an operation took
+	OBJ RUNS	Length of time a call to process an object event took
+	RETRV DLY	Time between an requesting a read and lookup completing
+	RETRIEVLS	Time between beginning and end of a retrieval
+
+     Each row shows the number of events that took a particular range of times.
+     Each step is 1 jiffy in size.  The JIFS column indicates the particular
+     jiffy range covered, and the SECS field the equivalent number of seconds.
+
+
+===========
+OBJECT LIST
+===========
+
+If CONFIG_FSCACHE_OBJECT_LIST is enabled, the FS-Cache facility will maintain a
+list of all the objects currently allocated and allow them to be viewed
+through:
+
+	/proc/fs/fscache/objects
+
+This will look something like:
+
+	[root@andromeda ~]# head /proc/fs/fscache/objects
+	OBJECT   PARENT   STAT CHLDN OPS OOP IPR EX READS EM EV F S | NETFS_COOKIE_DEF TY FL NETFS_DATA       OBJECT_KEY, AUX_DATA
+	======== ======== ==== ===== === === === == ===== == == = = | ================ == == ================ ================
+	   17e4b        2 ACTV     0   0   0   0  0     0 7b  4 0 0 | NFS.fh           DT  0 ffff88001dd82820 010006017edcf8bbc93b43298fdfbe71e50b57b13a172c0117f38472, e567634700000000000000000000000063f2404a000000000000000000000000c9030000000000000000000063f2404a
+	   1693a        2 ACTV     0   0   0   0  0     0 7b  4 0 0 | NFS.fh           DT  0 ffff88002db23380 010006017edcf8bbc93b43298fdfbe71e50b57b1e0162c01a2df0ea6, 420ebc4a000000000000000000000000420ebc4a0000000000000000000000000e1801000000000000000000420ebc4a
+
+where the first set of columns before the '|' describe the object:
+
+	COLUMN	DESCRIPTION
+	=======	===============================================================
+	OBJECT	Object debugging ID (appears as OBJ%x in some debug messages)
+	PARENT	Debugging ID of parent object
+	STAT	Object state
+	CHLDN	Number of child objects of this object
+	OPS	Number of outstanding operations on this object
+	OOP	Number of outstanding child object management operations
+	IPR
+	EX	Number of outstanding exclusive operations
+	READS	Number of outstanding read operations
+	EM	Object's event mask
+	EV	Events raised on this object
+	F	Object flags
+	S	Object work item busy state mask (1:pending 2:running)
+
+and the second set of columns describe the object's cookie, if present:
+
+	COLUMN		DESCRIPTION
+	===============	=======================================================
+	NETFS_COOKIE_DEF Name of netfs cookie definition
+	TY		Cookie type (IX - index, DT - data, hex - special)
+	FL		Cookie flags
+	NETFS_DATA	Netfs private data stored in the cookie
+	OBJECT_KEY	Object key	} 1 column, with separating comma
+	AUX_DATA	Object aux data	} presence may be configured
+
+The data shown may be filtered by attaching the a key to an appropriate keyring
+before viewing the file.  Something like:
+
+		keyctl add user fscache:objlist <restrictions> @s
+
+where <restrictions> are a selection of the following letters:
+
+	K	Show hexdump of object key (don't show if not given)
+	A	Show hexdump of object aux data (don't show if not given)
+
+and the following paired letters:
+
+	C	Show objects that have a cookie
+	c	Show objects that don't have a cookie
+	B	Show objects that are busy
+	b	Show objects that aren't busy
+	W	Show objects that have pending writes
+	w	Show objects that don't have pending writes
+	R	Show objects that have outstanding reads
+	r	Show objects that don't have outstanding reads
+	S	Show objects that have work queued
+	s	Show objects that don't have work queued
+
+If neither side of a letter pair is given, then both are implied.  For example:
+
+	keyctl add user fscache:objlist KB @s
+
+shows objects that are busy, and lists their object keys, but does not dump
+their auxiliary data.  It also implies "CcWwRrSs", but as 'B' is given, 'b' is
+not implied.
+
+By default all objects and all fields will be shown.
+
+
+=========
+DEBUGGING
+=========
+
+If CONFIG_FSCACHE_DEBUG is enabled, the FS-Cache facility can have runtime
+debugging enabled by adjusting the value in:
+
+	/sys/module/fscache/parameters/debug
+
+This is a bitmask of debugging streams to enable:
+
+	BIT	VALUE	STREAM				POINT
+	=======	=======	===============================	=======================
+	0	1	Cache management		Function entry trace
+	1	2					Function exit trace
+	2	4					General
+	3	8	Cookie management		Function entry trace
+	4	16					Function exit trace
+	5	32					General
+	6	64	Page handling			Function entry trace
+	7	128					Function exit trace
+	8	256					General
+	9	512	Operation management		Function entry trace
+	10	1024					Function exit trace
+	11	2048					General
+
+The appropriate set of values should be OR'd together and the result written to
+the control file.  For example:
+
+	echo $((1|8|64)) >/sys/module/fscache/parameters/debug
+
+will turn on all function entry debugging.