Define and create inode-level cache data storage objects (as managed by
nfs_inode structs).

Each inode-level object is created in a superblock-level index object and is
itself a data storage object into which pages from the inode are stored.

The inode object key is the NFS file handle for the inode.

The inode object is given coherency data to carry in the auxiliary data
permitted by the cache.  This is a sequence made up of:

 (1) i_mtime from the NFS inode.

 (2) i_ctime from the NFS inode.

 (3) i_size from the NFS inode.

 (4) change_attr from the NFSv4 attribute data.

As the cache is a persistent cache, the auxiliary data is checked when a new
NFS in-memory inode is set up that matches an already existing data storage
object in the cache.  If the coherency data is the same, the on-disk object is
retained and used; if not, it is scrapped and a new one created.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Define and create superblock-level cache index objects (as managed by
nfs_server structs).

Each superblock object is created in a server level index object and is itself
an index into which inode-level objects are inserted.

Ideally there would be one superblock-level object per server, and the former
would be folded into the latter; however, since the "nosharecache" option
exists this isn't possible.

The superblock object key is a sequence consisting of:

 (1) Certain superblock s_flags.

 (2) Various connection parameters that serve to distinguish superblocks for
     sget().

 (3) The volume FSID.

 (4) The security flavour.

 (5) The uniquifier length.

 (6) The uniquifier text.  This is normally an empty string, unless the fsc=xyz
     mount option was used to explicitly specify a uniquifier.

The key blob is of variable length, depending on the length of (6).

The superblock object is given no coherency data to carry in the auxiliary data
permitted by the cache.  It is assumed that the superblock is always coherent.

This patch also adds uniquification handling such that two otherwise identical
superblocks, at least one of which is marked "nosharecache", won't end up
trying to share the on-disk cache.  It will be possible to manually provide a
uniquifier through a mount option with a later patch to avoid the error
otherwise produced.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Define and create server-level cache index objects (as managed by nfs_client
structs).

Each server object is created in the NFS top-level index object and is itself
an index into which superblock-level objects are inserted.

Ideally there would be one superblock-level object per server, and the former
would be folded into the latter; however, since the "nosharecache" option
exists this isn't possible.

The server object key is a sequence consisting of:

 (1) NFS version

 (2) Server address family (eg: AF_INET or AF_INET6)

 (3) Server port.

 (4) Server IP address.

The key blob is of variable length, depending on the length of (4).

The server object is given no coherency data to carry in the auxiliary data
permitted by the cache.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Register NFS for caching and retrieve the top-level cache index object cookie.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Permit local filesystem caching to be enabled for NFS in the kernel
configuration.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Add FS-Cache option bit to nfs_server struct.  This is set to indicate local
on-disk caching is enabled for a particular superblock.

Also add debug bit for local caching operations.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Add comment banners to some NFS functions so that they can be modified by the
NFS fscache patches for further information.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

The attached patch makes the kAFS filesystem in fs/afs/ use FS-Cache, and
through it any attached caches.  The kAFS filesystem will use caching
automatically if it's available.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Add an FS-Cache cache-backend that permits a mounted filesystem to be used as a
backing store for the cache.

CacheFiles uses a userspace daemon to do some of the cache management - such as
reaping stale nodes and culling.  This is called cachefilesd and lives in
/sbin.  The source for the daemon can be downloaded from:

	http://people.redhat.com/~dhowells/cachefs/cachefilesd.c

And an example configuration from:

	http://people.redhat.com/~dhowells/cachefs/cachefilesd.conf

The filesystem and data integrity of the cache are only as good as those of the
filesystem providing the backing services.  Note that CacheFiles does not
attempt to journal anything since the journalling interfaces of the various
filesystems are very specific in nature.

CacheFiles creates a misc character device - "/dev/cachefiles" - that is used
to communication with the daemon.  Only one thing may have this open at once,
and whilst it is open, a cache is at least partially in existence.  The daemon
opens this and sends commands down it to control the cache.

CacheFiles is currently limited to a single cache.

CacheFiles attempts to maintain at least a certain percentage of free space on
the filesystem, shrinking the cache by culling the objects it contains to make
space if necessary - see the "Cache Culling" section.  This means it can be
placed on the same medium as a live set of data, and will expand to make use of
spare space and automatically contract when the set of data requires more
space.

============
REQUIREMENTS
============

The use of CacheFiles and its daemon requires the following features to be
available in the system and in the cache filesystem:

	- dnotify.

	- extended attributes (xattrs).

	- openat() and friends.

	- bmap() support on files in the filesystem (FIBMAP ioctl).

	- The use of bmap() to detect a partial page at the end of the file.

It is strongly recommended that the "dir_index" option is enabled on Ext3
filesystems being used as a cache.

=============
CONFIGURATION
=============

The cache is configured by a script in /etc/cachefilesd.conf.  These commands
set up cache ready for use.  The following script commands are available:

 (*) brun <N>%
 (*) bcull <N>%
 (*) bstop <N>%
 (*) frun <N>%
 (*) fcull <N>%
 (*) fstop <N>%

	Configure the culling limits.  Optional.  See the section on culling
	The defaults are 7% (run), 5% (cull) and 1% (stop) respectively.

	The commands beginning with a 'b' are file space (block) limits, those
	beginning with an 'f' are file count limits.

 (*) dir <path>

	Specify the directory containing the root of the cache.  Mandatory.

 (*) tag <name>

	Specify a tag to FS-Cache to use in distinguishing multiple caches.
	Optional.  The default is "CacheFiles".

 (*) debug <mask>

	Specify a numeric bitmask to control debugging in the kernel module.
	Optional.  The default is zero (all off).  The following values can be
	OR'd into the mask to collect various information:

		1	Turn on trace of function entry (_enter() macros)
		2	Turn on trace of function exit (_leave() macros)
		4	Turn on trace of internal debug points (_debug())

	This mask can also be set through sysfs, eg:

		echo 5 >/sys/modules/cachefiles/parameters/debug

==================
STARTING THE CACHE
==================

The cache is started by running the daemon.  The daemon opens the cache device,
configures the cache and tells it to begin caching.  At that point the cache
binds to fscache and the cache becomes live.

The daemon is run as follows:

	/sbin/cachefilesd [-d]* [-s] [-n] [-f <configfile>]

The flags are:

 (*) -d

	Increase the debugging level.  This can be specified multiple times and
	is cumulative with itself.

 (*) -s

	Send messages to stderr instead of syslog.

 (*) -n

	Don't daemonise and go into background.

 (*) -f <configfile>

	Use an alternative configuration file rather than the default one.

===============
THINGS TO AVOID
===============

Do not mount other things within the cache as this will cause problems.  The
kernel module contains its own very cut-down path walking facility that ignores
mountpoints, but the daemon can't avoid them.

Do not create, rename or unlink files and directories in the cache whilst the
cache is active, as this may cause the state to become uncertain.

Renaming files in the cache might make objects appear to be other objects (the
filename is part of the lookup key).

Do not change or remove the extended attributes attached to cache files by the
cache as this will cause the cache state management to get confused.

Do not create files or directories in the cache, lest the cache get confused or
serve incorrect data.

Do not chmod files in the cache.  The module creates things with minimal
permissions to prevent random users being able to access them directly.

=============
CACHE CULLING
=============

The cache may need culling occasionally to make space.  This involves
discarding objects from the cache that have been used less recently than
anything else.  Culling is based on the access time of data objects.  Empty
directories are culled if not in use.

Cache culling is done on the basis of the percentage of blocks and the
percentage of files available in the underlying filesystem.  There are six
"limits":

 (*) brun
 (*) frun

     If the amount of free space and the number of available files in the cache
     rises above both these limits, then culling is turned off.

 (*) bcull
 (*) fcull

     If the amount of available space or the number of available files in the
     cache falls below either of these limits, then culling is started.

 (*) bstop
 (*) fstop

     If the amount of available space or the number of available files in the
     cache falls below either of these limits, then no further allocation of
     disk space or files is permitted until culling has raised things above
     these limits again.

These must be configured thusly:

	0 <= bstop < bcull < brun < 100
	0 <= fstop < fcull < frun < 100

Note that these are percentages of available space and available files, and do
_not_ appear as 100 minus the percentage displayed by the "df" program.

The userspace daemon scans the cache to build up a table of cullable objects.
These are then culled in least recently used order.  A new scan of the cache is
started as soon as space is made in the table.  Objects will be skipped if
their atimes have changed or if the kernel module says it is still using them.

===============
CACHE STRUCTURE
===============

The CacheFiles module will create two directories in the directory it was
given:

 (*) cache/

 (*) graveyard/

The active cache objects all reside in the first directory.  The CacheFiles
kernel module moves any retired or culled objects that it can't simply unlink
to the graveyard from which the daemon will actually delete them.

The daemon uses dnotify to monitor the graveyard directory, and will delete
anything that appears therein.

The module represents index objects as directories with the filename "I..." or
"J...".  Note that the "cache/" directory is itself a special index.

Data objects are represented as files if they have no children, or directories
if they do.  Their filenames all begin "D..." or "E...".  If represented as a
directory, data objects will have a file in the directory called "data" that
actually holds the data.

Special objects are similar to data objects, except their filenames begin
"S..." or "T...".

If an object has children, then it will be represented as a directory.
Immediately in the representative directory are a collection of directories
named for hash values of the child object keys with an '@' prepended.  Into
this directory, if possible, will be placed the representations of the child
objects:

	INDEX     INDEX      INDEX                             DATA FILES
	========= ========== ================================= ================
	cache/@4a/I03nfs/@30/Ji000000000000000--fHg8hi8400
	cache/@4a/I03nfs/@30/Ji000000000000000--fHg8hi8400/@75/Es0g000w...DB1ry
	cache/@4a/I03nfs/@30/Ji000000000000000--fHg8hi8400/@75/Es0g000w...N22ry
	cache/@4a/I03nfs/@30/Ji000000000000000--fHg8hi8400/@75/Es0g000w...FP1ry

If the key is so long that it exceeds NAME_MAX with the decorations added on to
it, then it will be cut into pieces, the first few of which will be used to
make a nest of directories, and the last one of which will be the objects
inside the last directory.  The names of the intermediate directories will have
'+' prepended:

	J1223/@23/+xy...z/+kl...m/Epqr

Note that keys are raw data, and not only may they exceed NAME_MAX in size,
they may also contain things like '/' and NUL characters, and so they may not
be suitable for turning directly into a filename.

To handle this, CacheFiles will use a suitably printable filename directly and
"base-64" encode ones that aren't directly suitable.  The two versions of
object filenames indicate the encoding:

	OBJECT TYPE	PRINTABLE	ENCODED
	===============	===============	===============
	Index		"I..."		"J..."
	Data		"D..."		"E..."
	Special		"S..."		"T..."

Intermediate directories are always "@" or "+" as appropriate.

Each object in the cache has an extended attribute label that holds the object
type ID (required to distinguish special objects) and the auxiliary data from
the netfs.  The latter is used to detect stale objects in the cache and update
or retire them.

Note that CacheFiles will erase from the cache any file it doesn't recognise or
any file of an incorrect type (such as a FIFO file or a device file).

==========================
SECURITY MODEL AND SELINUX
==========================

CacheFiles is implemented to deal properly with the LSM security features of
the Linux kernel and the SELinux facility.

One of the problems that CacheFiles faces is that it is generally acting on
behalf of a process, and running in that process's context, and that includes a
security context that is not appropriate for accessing the cache - either
because the files in the cache are inaccessible to that process, or because if
the process creates a file in the cache, that file may be inaccessible to other
processes.

The way CacheFiles works is to temporarily change the security context (fsuid,
fsgid and actor security label) that the process acts as - without changing the
security context of the process when it the target of an operation performed by
some other process (so signalling and suchlike still work correctly).

When the CacheFiles module is asked to bind to its cache, it:

 (1) Finds the security label attached to the root cache directory and uses
     that as the security label with which it will create files.  By default,
     this is:

	cachefiles_var_t

 (2) Finds the security label of the process which issued the bind request
     (presumed to be the cachefilesd daemon), which by default will be:

	cachefilesd_t

     and asks LSM to supply a security ID as which it should act given the
     daemon's label.  By default, this will be:

	cachefiles_kernel_t

     SELinux transitions the daemon's security ID to the module's security ID
     based on a rule of this form in the policy.

	type_transition <daemon's-ID> kernel_t : process <module's-ID>;

     For instance:

	type_transition cachefilesd_t kernel_t : process cachefiles_kernel_t;

The module's security ID gives it permission to create, move and remove files
and directories in the cache, to find and access directories and files in the
cache, to set and access extended attributes on cache objects, and to read and
write files in the cache.

The daemon's security ID gives it only a very restricted set of permissions: it
may scan directories, stat files and erase files and directories.  It may
not read or write files in the cache, and so it is precluded from accessing the
data cached therein; nor is it permitted to create new files in the cache.

There are policy source files available in:

	http://people.redhat.com/~dhowells/fscache/cachefilesd-0.8.tar.bz2

and later versions.  In that tarball, see the files:

	cachefilesd.te
	cachefilesd.fc
	cachefilesd.if

They are built and installed directly by the RPM.

If a non-RPM based system is being used, then copy the above files to their own
directory and run:

	make -f /usr/share/selinux/devel/Makefile
	semodule -i cachefilesd.pp

You will need checkpolicy and selinux-policy-devel installed prior to the
build.

By default, the cache is located in /var/fscache, but if it is desirable that
it should be elsewhere, than either the above policy files must be altered, or
an auxiliary policy must be installed to label the alternate location of the
cache.

For instructions on how to add an auxiliary policy to enable the cache to be
located elsewhere when SELinux is in enforcing mode, please see:

	/usr/share/doc/cachefilesd-*/move-cache.txt

When the cachefilesd rpm is installed; alternatively, the document can be found
in the sources.

==================
A NOTE ON SECURITY
==================

CacheFiles makes use of the split security in the task_struct.  It allocates
its own task_security structure, and redirects current->act_as to point to it
when it acts on behalf of another process, in that process's context.

The reason it does this is that it calls vfs_mkdir() and suchlike rather than
bypassing security and calling inode ops directly.  Therefore the VFS and LSM
may deny the CacheFiles access to the cache data because under some
circumstances the caching code is running in the security context of whatever
process issued the original syscall on the netfs.

Furthermore, should CacheFiles create a file or directory, the security
parameters with that object is created (UID, GID, security label) would be
derived from that process that issued the system call, thus potentially
preventing other processes from accessing the cache - including CacheFiles's
cache management daemon (cachefilesd).

What is required is to temporarily override the security of the process that
issued the system call.  We can't, however, just do an in-place change of the
security data as that affects the process as an object, not just as a subject.
This means it may lose signals or ptrace events for example, and affects what
the process looks like in /proc.

So CacheFiles makes use of a logical split in the security between the
objective security (task->sec) and the subjective security (task->act_as).  The
objective security holds the intrinsic security properties of a process and is
never overridden.  This is what appears in /proc, and is what is used when a
process is the target of an operation by some other process (SIGKILL for
example).

The subjective security holds the active security properties of a process, and
may be overridden.  This is not seen externally, and is used whan a process
acts upon another object, for example SIGKILLing another process or opening a
file.

LSM hooks exist that allow SELinux (or Smack or whatever) to reject a request
for CacheFiles to run in a context of a specific security label, or to create
files and directories with another security label.

This documentation is added by the patch to:

	Documentation/filesystems/caching/cachefiles.txt
Signed-Off-By: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Export a number of functions for CacheFiles's use.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NRik van Riel <riel@redhat.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Add a function to install a monitor on the page lock waitqueue for a particular
page, thus allowing the page being unlocked to be detected.

This is used by CacheFiles to detect read completion on a page in the backing
filesystem so that it can then copy the data to the waiting netfs page.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NRik van Riel <riel@redhat.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Implement the data I/O part of the FS-Cache netfs API.  The documentation and
API header file were added in a previous patch.

This patch implements the following functions for the netfs to call:

 (*) fscache_attr_changed().

     Indicate that the object has changed its attributes.  The only attribute
     currently recorded is the file size.  Only pages within the set file size
     will be stored in the cache.

     This operation is submitted for asynchronous processing, and will return
     immediately.  It will return -ENOMEM if an out of memory error is
     encountered, -ENOBUFS if the object is not actually cached, or 0 if the
     operation is successfully queued.

 (*) fscache_read_or_alloc_page().
 (*) fscache_read_or_alloc_pages().

     Request data be fetched from the disk, and allocate internal metadata to
     track the netfs pages and reserve disk space for unknown pages.

     These operations perform semi-asynchronous data reads.  Upon returning
     they will indicate which pages they think can be retrieved from disk, and
     will have set in progress attempts to retrieve those pages.

     These will return, in order of preference, -ENOMEM on memory allocation
     error, -ERESTARTSYS if a signal interrupted proceedings, -ENODATA if one
     or more requested pages are not yet cached, -ENOBUFS if the object is not
     actually cached or if there isn't space for future pages to be cached on
     this object, or 0 if successful.

     In the case of the multipage function, the pages for which reads are set
     in progress will be removed from the list and the page count decreased
     appropriately.

     If any read operations should fail, the completion function will be given
     an error, and will also be passed contextual information to allow the
     netfs to fall back to querying the server for the absent pages.

     For each successful read, the page completion function will also be
     called.

     Any pages subsequently tracked by the cache will have PG_fscache set upon
     them on return.  fscache_uncache_page() must be called for such pages.

     If supplied by the netfs, the mark_pages_cached() cookie op will be
     invoked for any pages now tracked.

 (*) fscache_alloc_page().

     Allocate internal metadata to track a netfs page and reserve disk space.

     This will return -ENOMEM on memory allocation error, -ERESTARTSYS on
     signal, -ENOBUFS if the object isn't cached, or there isn't enough space
     in the cache, or 0 if successful.

     Any pages subsequently tracked by the cache will have PG_fscache set upon
     them on return.  fscache_uncache_page() must be called for such pages.

     If supplied by the netfs, the mark_pages_cached() cookie op will be
     invoked for any pages now tracked.

 (*) fscache_write_page().

     Request data be stored to disk.  This may only be called on pages that
     have been read or alloc'd by the above three functions and have not yet
     been uncached.

     This will return -ENOMEM on memory allocation error, -ERESTARTSYS on
     signal, -ENOBUFS if the object isn't cached, or there isn't immediately
     enough space in the cache, or 0 if successful.

     On a successful return, this operation will have queued the page for
     asynchronous writing to the cache.  The page will be returned with
     PG_fscache_write set until the write completes one way or another.  The
     caller will not be notified if the write fails due to an I/O error.  If
     that happens, the object will become available and all pending writes will
     be aborted.

     Note that the cache may batch up page writes, and so it may take a while
     to get around to writing them out.

     The caller must assume that until PG_fscache_write is cleared the page is
     use by the cache.  Any changes made to the page may be reflected on disk.
     The page may even be under DMA.

 (*) fscache_uncache_page().

     Indicate that the cache should stop tracking a page previously read or
     alloc'd from the cache.  If the page was alloc'd only, but unwritten, it
     will not appear on disk.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Add and document asynchronous operation handling for use by FS-Cache's data
storage and retrieval routines.

The following documentation is added to:

	Documentation/filesystems/caching/operations.txt

		       ================================
		       ASYNCHRONOUS OPERATIONS HANDLING
		       ================================

========
OVERVIEW
========

FS-Cache has an asynchronous operations handling facility that it uses for its
data storage and retrieval routines.  Its operations are represented by
fscache_operation structs, though these are usually embedded into some other
structure.

This facility is available to and expected to be be used by the cache backends,
and FS-Cache will create operations and pass them off to the appropriate cache
backend for completion.

To make use of this facility, <linux/fscache-cache.h> should be #included.

===============================
OPERATION RECORD INITIALISATION
===============================

An operation is recorded in an fscache_operation struct:

	struct fscache_operation {
		union {
			struct work_struct fast_work;
			struct slow_work slow_work;
		};
		unsigned long		flags;
		fscache_operation_processor_t processor;
		...
	};

Someone wanting to issue an operation should allocate something with this
struct embedded in it.  They should initialise it by calling:

	void fscache_operation_init(struct fscache_operation *op,
				    fscache_operation_release_t release);

with the operation to be initialised and the release function to use.

The op->flags parameter should be set to indicate the CPU time provision and
the exclusivity (see the Parameters section).

The op->fast_work, op->slow_work and op->processor flags should be set as
appropriate for the CPU time provision (see the Parameters section).

FSCACHE_OP_WAITING may be set in op->flags prior to each submission of the
operation and waited for afterwards.

==========
PARAMETERS
==========

There are a number of parameters that can be set in the operation record's flag
parameter.  There are three options for the provision of CPU time in these
operations:

 (1) The operation may be done synchronously (FSCACHE_OP_MYTHREAD).  A thread
     may decide it wants to handle an operation itself without deferring it to
     another thread.

     This is, for example, used in read operations for calling readpages() on
     the backing filesystem in CacheFiles.  Although readpages() does an
     asynchronous data fetch, the determination of whether pages exist is done
     synchronously - and the netfs does not proceed until this has been
     determined.

     If this option is to be used, FSCACHE_OP_WAITING must be set in op->flags
     before submitting the operation, and the operating thread must wait for it
     to be cleared before proceeding:

		wait_on_bit(&op->flags, FSCACHE_OP_WAITING,
			    fscache_wait_bit, TASK_UNINTERRUPTIBLE);

 (2) The operation may be fast asynchronous (FSCACHE_OP_FAST), in which case it
     will be given to keventd to process.  Such an operation is not permitted
     to sleep on I/O.

     This is, for example, used by CacheFiles to copy data from a backing fs
     page to a netfs page after the backing fs has read the page in.

     If this option is used, op->fast_work and op->processor must be
     initialised before submitting the operation:

		INIT_WORK(&op->fast_work, do_some_work);

 (3) The operation may be slow asynchronous (FSCACHE_OP_SLOW), in which case it
     will be given to the slow work facility to process.  Such an operation is
     permitted to sleep on I/O.

     This is, for example, used by FS-Cache to handle background writes of
     pages that have just been fetched from a remote server.

     If this option is used, op->slow_work and op->processor must be
     initialised before submitting the operation:

		fscache_operation_init_slow(op, processor)

Furthermore, operations may be one of two types:

 (1) Exclusive (FSCACHE_OP_EXCLUSIVE).  Operations of this type may not run in
     conjunction with any other operation on the object being operated upon.

     An example of this is the attribute change operation, in which the file
     being written to may need truncation.

 (2) Shareable.  Operations of this type may be running simultaneously.  It's
     up to the operation implementation to prevent interference between other
     operations running at the same time.

=========
PROCEDURE
=========

Operations are used through the following procedure:

 (1) The submitting thread must allocate the operation and initialise it
     itself.  Normally this would be part of a more specific structure with the
     generic op embedded within.

 (2) The submitting thread must then submit the operation for processing using
     one of the following two functions:

	int fscache_submit_op(struct fscache_object *object,
			      struct fscache_operation *op);

	int fscache_submit_exclusive_op(struct fscache_object *object,
					struct fscache_operation *op);

     The first function should be used to submit non-exclusive ops and the
     second to submit exclusive ones.  The caller must still set the
     FSCACHE_OP_EXCLUSIVE flag.

     If successful, both functions will assign the operation to the specified
     object and return 0.  -ENOBUFS will be returned if the object specified is
     permanently unavailable.

     The operation manager will defer operations on an object that is still
     undergoing lookup or creation.  The operation will also be deferred if an
     operation of conflicting exclusivity is in progress on the object.

     If the operation is asynchronous, the manager will retain a reference to
     it, so the caller should put their reference to it by passing it to:

	void fscache_put_operation(struct fscache_operation *op);

 (3) If the submitting thread wants to do the work itself, and has marked the
     operation with FSCACHE_OP_MYTHREAD, then it should monitor
     FSCACHE_OP_WAITING as described above and check the state of the object if
     necessary (the object might have died whilst the thread was waiting).

     When it has finished doing its processing, it should call
     fscache_put_operation() on it.

 (4) The operation holds an effective lock upon the object, preventing other
     exclusive ops conflicting until it is released.  The operation can be
     enqueued for further immediate asynchronous processing by adjusting the
     CPU time provisioning option if necessary, eg:

	op->flags &= ~FSCACHE_OP_TYPE;
	op->flags |= ~FSCACHE_OP_FAST;

     and calling:

	void fscache_enqueue_operation(struct fscache_operation *op)

     This can be used to allow other things to have use of the worker thread
     pools.

=====================
ASYNCHRONOUS CALLBACK
=====================

When used in asynchronous mode, the worker thread pool will invoke the
processor method with a pointer to the operation.  This should then get at the
container struct by using container_of():

	static void fscache_write_op(struct fscache_operation *_op)
	{
		struct fscache_storage *op =
			container_of(_op, struct fscache_storage, op);
	...
	}

The caller holds a reference on the operation, and will invoke
fscache_put_operation() when the processor function returns.  The processor
function is at liberty to call fscache_enqueue_operation() or to take extra
references.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Implement the cookie management part of the FS-Cache netfs client API.  The
documentation and API header file were added in a previous patch.

This patch implements the following three functions:

 (1) fscache_acquire_cookie().

     Acquire a cookie to represent an object to the netfs.  If the object in
     question is a non-index object, then that object and its parent indices
     will be created on disk at this point if they don't already exist.  Index
     creation is deferred because an index may reside in multiple caches.

 (2) fscache_relinquish_cookie().

     Retire or release a cookie previously acquired.  At this point, the
     object on disk may be destroyed.

 (3) fscache_update_cookie().

     Update the in-cache representation of a cookie.  This is used to update
     the auxiliary data for coherency management purposes.

With this patch it is possible to have a netfs instruct a cache backend to
look up, validate and create metadata on disk and to destroy it again.
The ability to actually store and retrieve data in the objects so created is
added in later patches.

Note that these functions will never return an error.  _All_ errors are
handled internally to FS-Cache.

The worst that can happen is that fscache_acquire_cookie() may return a NULL
pointer - which is considered a negative cookie pointer and can be passed back
to any function that takes a cookie without harm.  A negative cookie pointer
merely suppresses caching at that level.

The stub in linux/fscache.h will detect inline the negative cookie pointer and
abort the operation as fast as possible.  This means that the compiler doesn't
have to set up for a call in that case.

See the documentation in Documentation/filesystems/caching/netfs-api.txt for
more information.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Implement the cache object management state machine.

The following documentation is added to illuminate the working of this state
machine.  It will also be added as:

	Documentation/filesystems/caching/object.txt

	     ====================================================
	     IN-KERNEL CACHE OBJECT REPRESENTATION AND MANAGEMENT
	     ====================================================

==============
REPRESENTATION
==============

FS-Cache maintains an in-kernel representation of each object that a netfs is
currently interested in.  Such objects are represented by the fscache_cookie
struct and are referred to as cookies.

FS-Cache also maintains a separate in-kernel representation of the objects that
a cache backend is currently actively caching.  Such objects are represented by
the fscache_object struct.  The cache backends allocate these upon request, and
are expected to embed them in their own representations.  These are referred to
as objects.

There is a 1:N relationship between cookies and objects.  A cookie may be
represented by multiple objects - an index may exist in more than one cache -
or even by no objects (it may not be cached).

Furthermore, both cookies and objects are hierarchical.  The two hierarchies
correspond, but the cookies tree is a superset of the union of the object trees
of multiple caches:

	    NETFS INDEX TREE               :      CACHE 1     :      CACHE 2
	                                   :                  :
	                                   :   +-----------+  :
	                          +----------->|  IObject  |  :
	      +-----------+       |        :   +-----------+  :
	      |  ICookie  |-------+        :         |        :
	      +-----------+       |        :         |        :   +-----------+
	            |             +------------------------------>|  IObject  |
	            |                      :         |        :   +-----------+
	            |                      :         V        :         |
	            |                      :   +-----------+  :         |
	            V             +----------->|  IObject  |  :         |
	      +-----------+       |        :   +-----------+  :         |
	      |  ICookie  |-------+        :         |        :         V
	      +-----------+       |        :         |        :   +-----------+
	            |             +------------------------------>|  IObject  |
	      +-----+-----+                :         |        :   +-----------+
	      |           |                :         |        :         |
	      V           |                :         V        :         |
	+-----------+     |                :   +-----------+  :         |
	|  ICookie  |------------------------->|  IObject  |  :         |
	+-----------+     |                :   +-----------+  :         |
	      |           V                :         |        :         V
	      |     +-----------+          :         |        :   +-----------+
	      |     |  ICookie  |-------------------------------->|  IObject  |
	      |     +-----------+          :         |        :   +-----------+
	      V           |                :         V        :         |
	+-----------+     |                :   +-----------+  :         |
	|  DCookie  |------------------------->|  DObject  |  :         |
	+-----------+     |                :   +-----------+  :         |
	                  |                :                  :         |
	          +-------+-------+        :                  :         |
	          |               |        :                  :         |
	          V               V        :                  :         V
	    +-----------+   +-----------+  :                  :   +-----------+
	    |  DCookie  |   |  DCookie  |------------------------>|  DObject  |
	    +-----------+   +-----------+  :                  :   +-----------+
	                                   :                  :

In the above illustration, ICookie and IObject represent indices and DCookie
and DObject represent data storage objects.  Indices may have representation in
multiple caches, but currently, non-index objects may not.  Objects of any type
may also be entirely unrepresented.

As far as the netfs API goes, the netfs is only actually permitted to see
pointers to the cookies.  The cookies themselves and any objects attached to
those cookies are hidden from it.

===============================
OBJECT MANAGEMENT STATE MACHINE
===============================

Within FS-Cache, each active object is managed by its own individual state
machine.  The state for an object is kept in the fscache_object struct, in
object->state.  A cookie may point to a set of objects that are in different
states.

Each state has an action associated with it that is invoked when the machine
wakes up in that state.  There are four logical sets of states:

 (1) Preparation: states that wait for the parent objects to become ready.  The
     representations are hierarchical, and it is expected that an object must
     be created or accessed with respect to its parent object.

 (2) Initialisation: states that perform lookups in the cache and validate
     what's found and that create on disk any missing metadata.

 (3) Normal running: states that allow netfs operations on objects to proceed
     and that update the state of objects.

 (4) Termination: states that detach objects from their netfs cookies, that
     delete objects from disk, that handle disk and system errors and that free
     up in-memory resources.

In most cases, transitioning between states is in response to signalled events.
When a state has finished processing, it will usually set the mask of events in
which it is interested (object->event_mask) and relinquish the worker thread.
Then when an event is raised (by calling fscache_raise_event()), if the event
is not masked, the object will be queued for processing (by calling
fscache_enqueue_object()).

PROVISION OF CPU TIME
---------------------

The work to be done by the various states is given CPU time by the threads of
the slow work facility (see Documentation/slow-work.txt).  This is used in
preference to the workqueue facility because:

 (1) Threads may be completely occupied for very long periods of time by a
     particular work item.  These state actions may be doing sequences of
     synchronous, journalled disk accesses (lookup, mkdir, create, setxattr,
     getxattr, truncate, unlink, rmdir, rename).

 (2) Threads may do little actual work, but may rather spend a lot of time
     sleeping on I/O.  This means that single-threaded and 1-per-CPU-threaded
     workqueues don't necessarily have the right numbers of threads.

LOCKING SIMPLIFICATION
----------------------

Because only one worker thread may be operating on any particular object's
state machine at once, this simplifies the locking, particularly with respect
to disconnecting the netfs's representation of a cache object (fscache_cookie)
from the cache backend's representation (fscache_object) - which may be
requested from either end.

=================
THE SET OF STATES
=================

The object state machine has a set of states that it can be in.  There are
preparation states in which the object sets itself up and waits for its parent
object to transit to a state that allows access to its children:

 (1) State FSCACHE_OBJECT_INIT.

     Initialise the object and wait for the parent object to become active.  In
     the cache, it is expected that it will not be possible to look an object
     up from the parent object, until that parent object itself has been looked
     up.

There are initialisation states in which the object sets itself up and accesses
disk for the object metadata:

 (2) State FSCACHE_OBJECT_LOOKING_UP.

     Look up the object on disk, using the parent as a starting point.
     FS-Cache expects the cache backend to probe the cache to see whether this
     object is represented there, and if it is, to see if it's valid (coherency
     management).

     The cache should call fscache_object_lookup_negative() to indicate lookup
     failure for whatever reason, and should call fscache_obtained_object() to
     indicate success.

     At the completion of lookup, FS-Cache will let the netfs go ahead with
     read operations, no matter whether the file is yet cached.  If not yet
     cached, read operations will be immediately rejected with ENODATA until
     the first known page is uncached - as to that point there can be no data
     to be read out of the cache for that file that isn't currently also held
     in the pagecache.

 (3) State FSCACHE_OBJECT_CREATING.

     Create an object on disk, using the parent as a starting point.  This
     happens if the lookup failed to find the object, or if the object's
     coherency data indicated what's on disk is out of date.  In this state,
     FS-Cache expects the cache to create

     The cache should call fscache_obtained_object() if creation completes
     successfully, fscache_object_lookup_negative() otherwise.

     At the completion of creation, FS-Cache will start processing write
     operations the netfs has queued for an object.  If creation failed, the
     write ops will be transparently discarded, and nothing recorded in the
     cache.

There are some normal running states in which the object spends its time
servicing netfs requests:

 (4) State FSCACHE_OBJECT_AVAILABLE.

     A transient state in which pending operations are started, child objects
     are permitted to advance from FSCACHE_OBJECT_INIT state, and temporary
     lookup data is freed.

 (5) State FSCACHE_OBJECT_ACTIVE.

     The normal running state.  In this state, requests the netfs makes will be
     passed on to the cache.

 (6) State FSCACHE_OBJECT_UPDATING.

     The state machine comes here to update the object in the cache from the
     netfs's records.  This involves updating the auxiliary data that is used
     to maintain coherency.

And there are terminal states in which an object cleans itself up, deallocates
memory and potentially deletes stuff from disk:

 (7) State FSCACHE_OBJECT_LC_DYING.

     The object comes here if it is dying because of a lookup or creation
     error.  This would be due to a disk error or system error of some sort.
     Temporary data is cleaned up, and the parent is released.

 (8) State FSCACHE_OBJECT_DYING.

     The object comes here if it is dying due to an error, because its parent
     cookie has been relinquished by the netfs or because the cache is being
     withdrawn.

     Any child objects waiting on this one are given CPU time so that they too
     can destroy themselves.  This object waits for all its children to go away
     before advancing to the next state.

 (9) State FSCACHE_OBJECT_ABORT_INIT.

     The object comes to this state if it was waiting on its parent in
     FSCACHE_OBJECT_INIT, but its parent died.  The object will destroy itself
     so that the parent may proceed from the FSCACHE_OBJECT_DYING state.

(10) State FSCACHE_OBJECT_RELEASING.
(11) State FSCACHE_OBJECT_RECYCLING.

     The object comes to one of these two states when dying once it is rid of
     all its children, if it is dying because the netfs relinquished its
     cookie.  In the first state, the cached data is expected to persist, and
     in the second it will be deleted.

(12) State FSCACHE_OBJECT_WITHDRAWING.

     The object transits to this state if the cache decides it wants to
     withdraw the object from service, perhaps to make space, but also due to
     error or just because the whole cache is being withdrawn.

(13) State FSCACHE_OBJECT_DEAD.

     The object transits to this state when the in-memory object record is
     ready to be deleted.  The object processor shouldn't ever see an object in
     this state.

THE SET OF EVENTS
-----------------

There are a number of events that can be raised to an object state machine:

 (*) FSCACHE_OBJECT_EV_UPDATE

     The netfs requested that an object be updated.  The state machine will ask
     the cache backend to update the object, and the cache backend will ask the
     netfs for details of the change through its cookie definition ops.

 (*) FSCACHE_OBJECT_EV_CLEARED

     This is signalled in two circumstances:

     (a) when an object's last child object is dropped and

     (b) when the last operation outstanding on an object is completed.

     This is used to proceed from the dying state.

 (*) FSCACHE_OBJECT_EV_ERROR

     This is signalled when an I/O error occurs during the processing of some
     object.

 (*) FSCACHE_OBJECT_EV_RELEASE
 (*) FSCACHE_OBJECT_EV_RETIRE

     These are signalled when the netfs relinquishes a cookie it was using.
     The event selected depends on whether the netfs asks for the backing
     object to be retired (deleted) or retained.

 (*) FSCACHE_OBJECT_EV_WITHDRAW

     This is signalled when the cache backend wants to withdraw an object.
     This means that the object will have to be detached from the netfs's
     cookie.

Because the withdrawing releasing/retiring events are all handled by the object
state machine, it doesn't matter if there's a collision with both ends trying
to sever the connection at the same time.  The state machine can just pick
which one it wants to honour, and that effects the other.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Add helpers for use with wait_on_bit().
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Add functions to register and unregister a network filesystem or other client
of the FS-Cache service.  This allocates and releases the cookie representing
the top-level index for a netfs, and makes it available to the netfs.

If the FS-Cache facility is disabled, then the calls are optimised away at
compile time.

Note that whilst this patch may appear to work with FS-Cache enabled and a
netfs attempting to use it, it will leak the cookie it allocates for the netfs
as fscache_relinquish_cookie() is implemented in a later patch.  This will
cause the slab code to emit a warning when the module is removed.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Provide a slab from which can be allocated the FS-Cache cookies that will be
presented to the netfs.

Also provide a slab constructor and a function to recursively discard a cookie
and its ancestor chain.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Implement the entry points by which a cache backend may initialise, add,
declare an error upon and withdraw a cache.

Further, an object is created in sysfs under which each cache added will get
an object created:

	/sys/fs/fscache/<cachetag>/

All of this is described in Documentation/filesystems/caching/backend-api.txt
added by a previous patch.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Implement two features of FS-Cache:

 (1) The ability to request and release cache tags - names by which a cache may
     be known to a netfs, and thus selected for use.

 (2) An internal function by which a cache is selected by consulting the netfs,
     if the netfs wishes to be consulted.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Add a description of the root index of the cache for later patches to make use
of.

The root index is owned by FS-Cache itself.  When a netfs requests caching
facilities, FS-Cache will, if one doesn't already exist, create an entry in
the root index with the key being the name of the netfs ("AFS" for example),
and the auxiliary data holding the index structure version supplied by the
netfs:

				     FSDEF
				       |
				 +-----------+
				 |           |
				NFS         AFS
			       [v=1]       [v=1]

If an entry with the appropriate name does already exist, the version is
compared.  If the version is different, the entire subtree from that entry
will be discarded and a new entry created.

The new entry will be an index, and a cookie referring to it will be passed to
the netfs.  This is then the root handle by which the netfs accesses the
cache.  It can create whatever objects it likes in that index, including
further indices.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Make FS-Cache create its /proc interface and present various statistical
information through it.  Also provide the functions for updating this
information.

These features are enabled by:

	CONFIG_FSCACHE_PROC
	CONFIG_FSCACHE_STATS
	CONFIG_FSCACHE_HISTOGRAM

The /proc directory for FS-Cache is also exported so that caching modules can
add their own statistics there too.

The FS-Cache module is loadable at this point, and the statistics files can be
examined by userspace:

	cat /proc/fs/fscache/stats
	cat /proc/fs/fscache/histogram
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Add the main configuration option, allowing FS-Cache to be selected; the
module entry and exit functions and the debugging stuff used by these patches.

The two configuration options added are:

	CONFIG_FSCACHE
	CONFIG_FSCACHE_DEBUG

The first enables the facility, and the second makes the debugging statements
enableable through the "debug" module parameter.  The value of this parameter
is a bitmask as described in:

	Documentation/filesystems/caching/fscache.txt

The module can be loaded at this point, but all it will do at this point in
the patch series is to start up the slow work facility and shut it down again.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

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: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Add the API for a generic facility (FS-Cache) by which filesystems (such as AFS
or NFS) may call on local caching capabilities without having to know anything
about how the cache works, or even if there is a cache:

	+---------+
	|         |                        +--------------+
	|   NFS   |--+                     |              |
	|         |  |                 +-->|   CacheFS    |
	+---------+  |   +----------+  |   |  /dev/hda5   |
	             |   |          |  |   +--------------+
	+---------+  +-->|          |  |
	|         |      |          |--+
	|   AFS   |----->| FS-Cache |
	|         |      |          |--+
	+---------+  +-->|          |  |
	             |   |          |  |   +--------------+
	+---------+  |   +----------+  |   |              |
	|         |  |                 +-->|  CacheFiles  |
	|  ISOFS  |--+                     |  /var/cache  |
	|         |                        +--------------+
	+---------+

General documentation and documentation of the netfs specific API are provided
in addition to the header files.

As this patch stands, it is possible to build a filesystem against the facility
and attempt to use it.  All that will happen is that all requests will be
immediately denied as if no cache is present.

Further patches will implement the core of the facility.  The facility will
transfer requests from networking filesystems to appropriate caches if
possible, or else gracefully deny them.

If this facility is disabled in the kernel configuration, then all its
operations will trivially reduce to nothing during compilation.

WHY NOT I_MAPPING?
==================

I have added my own API to implement caching rather than using i_mapping to do
this for a number of reasons.  These have been discussed a lot on the LKML and
CacheFS mailing lists, but to summarise the basics:

 (1) Most filesystems don't do hole reportage.  Holes in files are treated as
     blocks of zeros and can't be distinguished otherwise, making it difficult
     to distinguish blocks that have been read from the network and cached from
     those that haven't.

 (2) The backing inode must be fully populated before being exposed to
     userspace through the main inode because the VM/VFS goes directly to the
     backing inode and does not interrogate the front inode's VM ops.

     Therefore:

     (a) The backing inode must fit entirely within the cache.

     (b) All backed files currently open must fit entirely within the cache at
     	 the same time.

     (c) A working set of files in total larger than the cache may not be
     	 cached.

     (d) A file may not grow larger than the available space in the cache.

     (e) A file that's open and cached, and remotely grows larger than the
     	 cache is potentially stuffed.

 (3) Writes go to the backing filesystem, and can only be transferred to the
     network when the file is closed.

 (4) There's no record of what changes have been made, so the whole file must
     be written back.

 (5) The pages belong to the backing filesystem, and all metadata associated
     with that page are relevant only to the backing filesystem, and not
     anything stacked atop it.

OVERVIEW
========

FS-Cache provides (or will provide) the following facilities:

 (1) Caches can be added / removed at any time, even whilst in use.

 (2) Adds a facility by which tags can be used to refer to caches, even if
     they're not available yet.

 (3) More than one cache can be used at once.  Caches can be selected
     explicitly by use of tags.

 (4) The netfs is provided with an interface that allows either party to
     withdraw caching facilities from a file (required for (1)).

 (5) A netfs may annotate cache objects that belongs to it.  This permits the
     storage of coherency maintenance data.

 (6) Cache objects will be pinnable and space reservations will be possible.

 (7) The interface to the netfs returns as few errors as possible, preferring
     rather to let the netfs remain oblivious.

 (8) 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.

 (9) 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.

(10) Indices can be used to group files together to reduce key size and to make
     group invalidation easier.  The use of indices may make lookup quicker,
     but that's cache dependent.

(11) Data I/O is effectively done directly 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.

(12) 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.

(13) 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.

FS-Cache maintains a virtual index 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, two netfs's can be seen to be backed: NFS and AFS.  These
have different index hierarchies:

 (*) The NFS primary index will probably contain 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 FS-Cache overview can be found in:

	Documentation/filesystems/caching/fscache.txt

The netfs API to FS-Cache can be found in:

	Documentation/filesystems/caching/netfs-api.txt
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Recruit a page flag to aid in cache management.  The following extra flag is
defined:

 (1) PG_fscache (PG_private_2)

     The marked page is backed by a local cache and is pinning resources in the
     cache driver.

If PG_fscache is set, then things that checked for PG_private will now also
check for that.  This includes things like truncation and page invalidation.
The function page_has_private() had been added to make the checks for both
PG_private and PG_private_2 at the same time.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NRik van Riel <riel@redhat.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

The attached patch causes read_cache_pages() to release page-private data on a
page for which add_to_page_cache() fails.  If the filler function fails, then
the problematic page is left attached to the pagecache (with appropriate flags
set, one presumes) and the remaining to-be-attached pages are invalidated and
discarded.  This permits pages with caching references associated with them to
be cleaned up.

The invalidatepage() address space op is called (indirectly) to do the honours.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NRik van Riel <riel@redhat.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Document the slow work thread pool.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Make the slow work pool configurable through /proc/sys/kernel/slow-work.

 (*) /proc/sys/kernel/slow-work/min-threads

     The minimum number of threads that should be in the pool as long as it is
     in use.  This may be anywhere between 2 and max-threads.

 (*) /proc/sys/kernel/slow-work/max-threads

     The maximum number of threads that should in the pool.  This may be
     anywhere between min-threads and 255 or NR_CPUS * 2, whichever is greater.

 (*) /proc/sys/kernel/slow-work/vslow-percentage

     The percentage of active threads in the pool that may be used to execute
     very slow work items.  This may be between 1 and 99.  The resultant number
     is bounded to between 1 and one fewer than the number of active threads.
     This ensures there is always at least one thread that can process very
     slow work items, and always at least one thread that won't.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSerge Hallyn <serue@us.ibm.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Make the slow-work thread pool actually dynamic in the number of threads it
contains.  With this patch, it will both create additional threads when it has
extra work to do, and cull excess threads that aren't doing anything.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSerge Hallyn <serue@us.ibm.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Create a dynamically sized pool of threads for doing very slow work items, such
as invoking mkdir() or rmdir() - things that may take a long time and may
sleep, holding mutexes/semaphores and hogging a thread, and are thus unsuitable
for workqueues.

The number of threads is always at least a settable minimum, but more are
started when there's more work to do, up to a limit.  Because of the nature of
the load, it's not suitable for a 1-thread-per-CPU type pool.  A system with
one CPU may well want several threads.

This is used by FS-Cache to do slow caching operations in the background, such
as looking up, creating or deleting cache objects.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSerge Hallyn <serue@us.ibm.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6:
  Remove two unneeded exports and make two symbols static in fs/mpage.c
  Cleanup after commit 585d3bc0
  Trim includes of fdtable.h
  Don't crap into descriptor table in binfmt_som
  Trim includes in binfmt_elf
  Don't mess with descriptor table in load_elf_binary()
  Get rid of indirect include of fs_struct.h
  New helper - current_umask()
  check_unsafe_exec() doesn't care about signal handlers sharing
  New locking/refcounting for fs_struct
  Take fs_struct handling to new file (fs/fs_struct.c)
  Get rid of bumping fs_struct refcount in pivot_root(2)
  Kill unsharing fs_struct in __set_personality()

* 'drm-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/airlied/drm-2.6: (21 commits)
  drm/radeon: load the right microcode on rs780
  drm: remove unused "can_grow" parameter from drm_crtc_helper_initial_config
  drm: fix EDID backward compat check
  drm: sync the mode validation for INTERLACE/DBLSCAN
  drm: fix typo in edid vendor parsing.
  DRM: drm_crtc_helper.h doesn't actually need i2c.h
  drm: fix missing inline function on 32-bit powerpc.
  drm: Use pgprot_writecombine in GEM GTT mapping to get the right bits for !PAT.
  drm/i915: Add a spinlock to protect the active_list
  drm/i915: Fix SDVO TV support
  drm/i915: Fix SDVO CREATE_PREFERRED_INPUT_TIMING command
  drm/i915: Fix error in SDVO DTD and modeline convert
  drm/i915: Fix SDVO command debug function
  drm/i915: fix TV mode setting in property change
  drm/i915: only set TV mode when any property changed
  drm/i915: clean up udelay usage
  drm/i915: add VGA hotplug support for 945+
  drm/i915: correctly set IGD device's gtt size for KMS.
  drm/i915: avoid hanging on to a stale pointer to raw_edid.
  drm/i915: check for -EINVAL from vm_insert_pfn
  ...

* git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-2.6: (54 commits)
  glge: remove unused #include <version.h>
  dnet: remove unused #include <version.h>
  tcp: miscounts due to tcp_fragment pcount reset
  tcp: add helper for counter tweaking due mid-wq change
  hso: fix for the 'invalid frame length' messages
  hso: fix for crash when unplugging the device
  fsl_pq_mdio: Fix compile failure
  fsl_pq_mdio: Revive UCC MDIO support
  ucc_geth: Pass proper device to DMA routines, otherwise oops happens
  i.MX31: Fixing cs89x0 network building to i.MX31ADS
  tc35815: Fix build error if NAPI enabled
  hso: add Vendor/Product ID's for new devices
  ucc_geth: Remove unused header
  gianfar: Remove unused header
  kaweth: Fix locking to be SMP-safe
  net: allow multiple dev per napi with GRO
  r8169: reset IntrStatus after chip reset
  ixgbe: Fix potential memory leak/driver panic issue while setting up Tx & Rx ring parameters
  ixgbe: fix ethtool -A|a behavior
  ixgbe: Patch to fix driver panic while freeing up tx & rx resources
  ...

Fix slab corruption caused by alloc_cpumask_var_node() overwriting the
tail end of an off-stack cpumask.

The function zeros out cpumask bits beyond the last possible cpu.  The
starting point for zeroing should be the beginning of the mask offset by a
byte count derived from the number of possible cpus.  The offset was
calculated in bits instead of bytes.  This resulted in overwriting the end
of the cpumask.
Signed-off-by: NJack Steiner <steiner@sgi.com>
Acked-by: Mike Travis <travis.sgi.com>
Acked-by: NIngo Molnar <mingo@elte.hu>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: <stable@kernel.org>		[2.6.29.x]
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Implement __raw_read_lock_flags and __raw_write_lock_flags for the ia64
architecture.

[kosaki.motohiro@jp.fujitsu.com: typo fix]
Signed-off-by: NPetr Tesarik <ptesarik@suse.cz>
Signed-off-by: NRobin Holt <holt@sgi.com>
Cc: <linux-arch@vger.kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: NTony Luck <tony.luck@intel.com>
Signed-off-by: NKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Pass the original flags to rwlock arch-code, so that it can re-enable
interrupts if implemented for that architecture.

Initially, make __raw_read_lock_flags and __raw_write_lock_flags stubs
which just do the same thing as non-flags variants.
Signed-off-by: NPetr Tesarik <ptesarik@suse.cz>
Signed-off-by: NRobin Holt <holt@sgi.com>
Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: <linux-arch@vger.kernel.org>
Acked-by: NIngo Molnar <mingo@elte.hu>
Cc: "Luck, Tony" <tony.luck@intel.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

SGI has observed that on large systems, interrupts are not serviced for a
long period of time when waiting for a rwlock.  The following patch series
re-enables irqs while waiting for the lock, resembling the code which is
already there for spinlocks.

I only made the ia64 version, because the patch adds some overhead to the
fast path.  I assume there is currently no demand to have this for other
architectures, because the systems are not so large.  Of course, the
possibility to implement raw_{read|write}_lock_flags for any architecture
is still there.

This patch:

The new macro LOCK_CONTENDED_FLAGS expands to the correct implementation
depending on the config options, so that IRQ's are re-enabled when
possible, but they remain disabled if CONFIG_LOCKDEP is set.
Signed-off-by: NPetr Tesarik <ptesarik@suse.cz>
Signed-off-by: NRobin Holt <holt@sgi.com>
Cc: <linux-arch@vger.kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: "Luck, Tony" <tony.luck@intel.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Make ufs return f_fsid info for statfs(2).
Signed-off-by: NColy Li <coly.li@suse.de>
Cc: Evgeniy Dushistov <dushistov@mail.ru>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Make sysv file system return f_fsid info for statfs(2).
Signed-off-by: NColy Li <coly.li@suse.de>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>