diff --git a/Documentation/filesystems/nfs/00-INDEX b/Documentation/filesystems/nfs/00-INDEX
new file mode 100644
index 0000000..53f3b59
--- /dev/null
+++ b/Documentation/filesystems/nfs/00-INDEX
@@ -0,0 +1,26 @@
+00-INDEX
+	- this file (nfs-related documentation).
+Exporting
+	- explanation of how to make filesystems exportable.
+fault_injection.txt
+	- information for using fault injection on the server
+knfsd-stats.txt
+	- statistics which the NFS server makes available to user space.
+nfs.txt
+	- nfs client, and DNS resolution for fs_locations.
+nfs41-server.txt
+	- info on the Linux server implementation of NFSv4 minor version 1.
+nfs-rdma.txt
+	- how to install and setup the Linux NFS/RDMA client and server software
+nfsd-admin-interfaces.txt
+	- Administrative interfaces for nfsd.
+nfsroot.txt
+	- short guide on setting up a diskless box with NFS root filesystem.
+pnfs.txt
+	- short explanation of some of the internals of the pnfs client code
+rpc-cache.txt
+	- introduction to the caching mechanisms in the sunrpc layer.
+idmapper.txt
+	- information for configuring request-keys to be used by idmapper
+rpc-server-gss.txt
+	- Information on GSS authentication support in the NFS Server
diff --git a/Documentation/filesystems/nfs/Exporting b/Documentation/filesystems/nfs/Exporting
new file mode 100644
index 0000000..6388914
--- /dev/null
+++ b/Documentation/filesystems/nfs/Exporting
@@ -0,0 +1,160 @@
+
+Making Filesystems Exportable
+=============================
+
+Overview
+--------
+
+All filesystem operations require a dentry (or two) as a starting
+point.  Local applications have a reference-counted hold on suitable
+dentries via open file descriptors or cwd/root.  However remote
+applications that access a filesystem via a remote filesystem protocol
+such as NFS may not be able to hold such a reference, and so need a
+different way to refer to a particular dentry.  As the alternative
+form of reference needs to be stable across renames, truncates, and
+server-reboot (among other things, though these tend to be the most
+problematic), there is no simple answer like 'filename'.
+
+The mechanism discussed here allows each filesystem implementation to
+specify how to generate an opaque (outside of the filesystem) byte
+string for any dentry, and how to find an appropriate dentry for any
+given opaque byte string.
+This byte string will be called a "filehandle fragment" as it
+corresponds to part of an NFS filehandle.
+
+A filesystem which supports the mapping between filehandle fragments
+and dentries will be termed "exportable".
+
+
+
+Dcache Issues
+-------------
+
+The dcache normally contains a proper prefix of any given filesystem
+tree.  This means that if any filesystem object is in the dcache, then
+all of the ancestors of that filesystem object are also in the dcache.
+As normal access is by filename this prefix is created naturally and
+maintained easily (by each object maintaining a reference count on
+its parent).
+
+However when objects are included into the dcache by interpreting a
+filehandle fragment, there is no automatic creation of a path prefix
+for the object.  This leads to two related but distinct features of
+the dcache that are not needed for normal filesystem access.
+
+1/ The dcache must sometimes contain objects that are not part of the
+   proper prefix. i.e that are not connected to the root.
+2/ The dcache must be prepared for a newly found (via ->lookup) directory
+   to already have a (non-connected) dentry, and must be able to move
+   that dentry into place (based on the parent and name in the
+   ->lookup).   This is particularly needed for directories as
+   it is a dcache invariant that directories only have one dentry.
+
+To implement these features, the dcache has:
+
+a/ A dentry flag DCACHE_DISCONNECTED which is set on
+   any dentry that might not be part of the proper prefix.
+   This is set when anonymous dentries are created, and cleared when a
+   dentry is noticed to be a child of a dentry which is in the proper
+   prefix.  If the refcount on a dentry with this flag set
+   becomes zero, the dentry is immediately discarded, rather than being
+   kept in the dcache.  If a dentry that is not already in the dcache
+   is repeatedly accessed by filehandle (as NFSD might do), an new dentry
+   will be a allocated for each access, and discarded at the end of
+   the access.
+
+   Note that such a dentry can acquire children, name, ancestors, etc.
+   without losing DCACHE_DISCONNECTED - that flag is only cleared when
+   subtree is successfully reconnected to root.  Until then dentries
+   in such subtree are retained only as long as there are references;
+   refcount reaching zero means immediate eviction, same as for unhashed
+   dentries.  That guarantees that we won't need to hunt them down upon
+   umount.
+
+b/ A primitive for creation of secondary roots - d_obtain_root(inode).
+   Those do _not_ bear DCACHE_DISCONNECTED.  They are placed on the
+   per-superblock list (->s_roots), so they can be located at umount
+   time for eviction purposes.
+
+c/ Helper routines to allocate anonymous dentries, and to help attach
+   loose directory dentries at lookup time. They are:
+    d_obtain_alias(inode) will return a dentry for the given inode.
+      If the inode already has a dentry, one of those is returned.
+      If it doesn't, a new anonymous (IS_ROOT and
+        DCACHE_DISCONNECTED) dentry is allocated and attached.
+      In the case of a directory, care is taken that only one dentry
+      can ever be attached.
+    d_splice_alias(inode, dentry) will introduce a new dentry into the tree;
+      either the passed-in dentry or a preexisting alias for the given inode
+      (such as an anonymous one created by d_obtain_alias), if appropriate.
+      It returns NULL when the passed-in dentry is used, following the calling
+      convention of ->lookup.
+ 
+Filesystem Issues
+-----------------
+
+For a filesystem to be exportable it must:
+ 
+   1/ provide the filehandle fragment routines described below.
+   2/ make sure that d_splice_alias is used rather than d_add
+      when ->lookup finds an inode for a given parent and name.
+
+      If inode is NULL, d_splice_alias(inode, dentry) is equivalent to
+
+		d_add(dentry, inode), NULL
+
+      Similarly, d_splice_alias(ERR_PTR(err), dentry) = ERR_PTR(err)
+
+      Typically the ->lookup routine will simply end with a:
+
+		return d_splice_alias(inode, dentry);
+	}
+
+
+
+  A file system implementation declares that instances of the filesystem
+are exportable by setting the s_export_op field in the struct
+super_block.  This field must point to a "struct export_operations"
+struct which has the following members:
+
+ encode_fh  (optional)
+    Takes a dentry and creates a filehandle fragment which can later be used
+    to find or create a dentry for the same object.  The default
+    implementation creates a filehandle fragment that encodes a 32bit inode
+    and generation number for the inode encoded, and if necessary the
+    same information for the parent.
+
+  fh_to_dentry (mandatory)
+    Given a filehandle fragment, this should find the implied object and
+    create a dentry for it (possibly with d_obtain_alias).
+
+  fh_to_parent (optional but strongly recommended)
+    Given a filehandle fragment, this should find the parent of the
+    implied object and create a dentry for it (possibly with
+    d_obtain_alias).  May fail if the filehandle fragment is too small.
+
+  get_parent (optional but strongly recommended)
+    When given a dentry for a directory, this should return  a dentry for
+    the parent.  Quite possibly the parent dentry will have been allocated
+    by d_alloc_anon.  The default get_parent function just returns an error
+    so any filehandle lookup that requires finding a parent will fail.
+    ->lookup("..") is *not* used as a default as it can leave ".." entries
+    in the dcache which are too messy to work with.
+
+  get_name (optional)
+    When given a parent dentry and a child dentry, this should find a name
+    in the directory identified by the parent dentry, which leads to the
+    object identified by the child dentry.  If no get_name function is
+    supplied, a default implementation is provided which uses vfs_readdir
+    to find potential names, and matches inode numbers to find the correct
+    match.
+
+
+A filehandle fragment consists of an array of 1 or more 4byte words,
+together with a one byte "type".
+The decode_fh routine should not depend on the stated size that is
+passed to it.  This size may be larger than the original filehandle
+generated by encode_fh, in which case it will have been padded with
+nuls.  Rather, the encode_fh routine should choose a "type" which
+indicates the decode_fh how much of the filehandle is valid, and how
+it should be interpreted.
diff --git a/Documentation/filesystems/nfs/fault_injection.txt b/Documentation/filesystems/nfs/fault_injection.txt
new file mode 100644
index 0000000..f3a5b0a
--- /dev/null
+++ b/Documentation/filesystems/nfs/fault_injection.txt
@@ -0,0 +1,69 @@
+
+Fault Injection
+===============
+Fault injection is a method for forcing errors that may not normally occur, or
+may be difficult to reproduce.  Forcing these errors in a controlled environment
+can help the developer find and fix bugs before their code is shipped in a
+production system.  Injecting an error on the Linux NFS server will allow us to
+observe how the client reacts and if it manages to recover its state correctly.
+
+NFSD_FAULT_INJECTION must be selected when configuring the kernel to use this
+feature.
+
+
+Using Fault Injection
+=====================
+On the client, mount the fault injection server through NFS v4.0+ and do some
+work over NFS (open files, take locks, ...).
+
+On the server, mount the debugfs filesystem to <debug_dir> and ls
+<debug_dir>/nfsd.  This will show a list of files that will be used for
+injecting faults on the NFS server.  As root, write a number n to the file
+corresponding to the action you want the server to take.  The server will then
+process the first n items it finds.  So if you want to forget 5 locks, echo '5'
+to <debug_dir>/nfsd/forget_locks.  A value of 0 will tell the server to forget
+all corresponding items.  A log message will be created containing the number
+of items forgotten (check dmesg).
+
+Go back to work on the client and check if the client recovered from the error
+correctly.
+
+
+Available Faults
+================
+forget_clients:
+     The NFS server keeps a list of clients that have placed a mount call.  If
+     this list is cleared, the server will have no knowledge of who the client
+     is, forcing the client to reauthenticate with the server.
+
+forget_openowners:
+     The NFS server keeps a list of what files are currently opened and who
+     they were opened by.  Clearing this list will force the client to reopen
+     its files.
+
+forget_locks:
+     The NFS server keeps a list of what files are currently locked in the VFS.
+     Clearing this list will force the client to reclaim its locks (files are
+     unlocked through the VFS as they are cleared from this list).
+
+forget_delegations:
+     A delegation is used to assure the client that a file, or part of a file,
+     has not changed since the delegation was awarded.  Clearing this list will
+     force the client to reacquire its delegation before accessing the file
+     again.
+
+recall_delegations:
+     Delegations can be recalled by the server when another client attempts to
+     access a file.  This test will notify the client that its delegation has
+     been revoked, forcing the client to reacquire the delegation before using
+     the file again.
+
+
+tools/nfs/inject_faults.sh script
+=================================
+This script has been created to ease the fault injection process.  This script
+will detect the mounted debugfs directory and write to the files located there
+based on the arguments passed by the user.  For example, running
+`inject_faults.sh forget_locks 1` as root will instruct the server to forget
+one lock.  Running `inject_faults forget_locks` will instruct the server to
+forgetall locks.
diff --git a/Documentation/filesystems/nfs/idmapper.txt b/Documentation/filesystems/nfs/idmapper.txt
new file mode 100644
index 0000000..b86831a
--- /dev/null
+++ b/Documentation/filesystems/nfs/idmapper.txt
@@ -0,0 +1,75 @@
+
+=========
+ID Mapper
+=========
+Id mapper is used by NFS to translate user and group ids into names, and to
+translate user and group names into ids.  Part of this translation involves
+performing an upcall to userspace to request the information.  There are two
+ways NFS could obtain this information: placing a call to /sbin/request-key
+or by placing a call to the rpc.idmap daemon.
+
+NFS will attempt to call /sbin/request-key first.  If this succeeds, the
+result will be cached using the generic request-key cache.  This call should
+only fail if /etc/request-key.conf is not configured for the id_resolver key
+type, see the "Configuring" section below if you wish to use the request-key
+method.
+
+If the call to /sbin/request-key fails (if /etc/request-key.conf is not
+configured with the id_resolver key type), then the idmapper will ask the
+legacy rpc.idmap daemon for the id mapping.  This result will be stored
+in a custom NFS idmap cache.
+
+
+===========
+Configuring
+===========
+The file /etc/request-key.conf will need to be modified so /sbin/request-key can
+direct the upcall.  The following line should be added:
+
+#OP	TYPE	DESCRIPTION	CALLOUT INFO	PROGRAM ARG1 ARG2 ARG3 ...
+#======	=======	===============	===============	===============================
+create	id_resolver	*	*		/usr/sbin/nfs.idmap %k %d 600
+
+This will direct all id_resolver requests to the program /usr/sbin/nfs.idmap.
+The last parameter, 600, defines how many seconds into the future the key will
+expire.  This parameter is optional for /usr/sbin/nfs.idmap.  When the timeout
+is not specified, nfs.idmap will default to 600 seconds.
+
+id mapper uses for key descriptions:
+	  uid:  Find the UID for the given user
+	  gid:  Find the GID for the given group
+	 user:  Find the user  name for the given UID
+	group:  Find the group name for the given GID
+
+You can handle any of these individually, rather than using the generic upcall
+program.  If you would like to use your own program for a uid lookup then you
+would edit your request-key.conf so it look similar to this:
+
+#OP	TYPE	DESCRIPTION	CALLOUT INFO	PROGRAM ARG1 ARG2 ARG3 ...
+#======	=======	===============	===============	===============================
+create	id_resolver	uid:*	*		/some/other/program %k %d 600
+create	id_resolver	*	*		/usr/sbin/nfs.idmap %k %d 600
+
+Notice that the new line was added above the line for the generic program.
+request-key will find the first matching line and corresponding program.  In
+this case, /some/other/program will handle all uid lookups and
+/usr/sbin/nfs.idmap will handle gid, user, and group lookups.
+
+See <file:Documentation/security/keys/request-key.rst> for more information
+about the request-key function.
+
+
+=========
+nfs.idmap
+=========
+nfs.idmap is designed to be called by request-key, and should not be run "by
+hand".  This program takes two arguments, a serialized key and a key
+description.  The serialized key is first converted into a key_serial_t, and
+then passed as an argument to keyctl_instantiate (both are part of keyutils.h).
+
+The actual lookups are performed by functions found in nfsidmap.h.  nfs.idmap
+determines the correct function to call by looking at the first part of the
+description string.  For example, a uid lookup description will appear as
+"uid:user@domain".
+
+nfs.idmap will return 0 if the key was instantiated, and non-zero otherwise.
diff --git a/Documentation/filesystems/nfs/knfsd-stats.txt b/Documentation/filesystems/nfs/knfsd-stats.txt
new file mode 100644
index 0000000..1a5d821
--- /dev/null
+++ b/Documentation/filesystems/nfs/knfsd-stats.txt
@@ -0,0 +1,123 @@
+
+Kernel NFS Server Statistics
+============================
+
+This document describes the format and semantics of the statistics
+which the kernel NFS server makes available to userspace.  These
+statistics are available in several text form pseudo files, each of
+which is described separately below.
+
+In most cases you don't need to know these formats, as the nfsstat(8)
+program from the nfs-utils distribution provides a helpful command-line
+interface for extracting and printing them.
+
+All the files described here are formatted as a sequence of text lines,
+separated by newline '\n' characters.  Lines beginning with a hash
+'#' character are comments intended for humans and should be ignored
+by parsing routines.  All other lines contain a sequence of fields
+separated by whitespace.
+
+/proc/fs/nfsd/pool_stats
+------------------------
+
+This file is available in kernels from 2.6.30 onwards, if the
+/proc/fs/nfsd filesystem is mounted (it almost always should be).
+
+The first line is a comment which describes the fields present in
+all the other lines.  The other lines present the following data as
+a sequence of unsigned decimal numeric fields.  One line is shown
+for each NFS thread pool.
+
+All counters are 64 bits wide and wrap naturally.  There is no way
+to zero these counters, instead applications should do their own
+rate conversion.
+
+pool
+	The id number of the NFS thread pool to which this line applies.
+	This number does not change.
+
+	Thread pool ids are a contiguous set of small integers starting
+	at zero.  The maximum value depends on the thread pool mode, but
+	currently cannot be larger than the number of CPUs in the system.
+	Note that in the default case there will be a single thread pool
+	which contains all the nfsd threads and all the CPUs in the system,
+	and thus this file will have a single line with a pool id of "0".
+
+packets-arrived
+	Counts how many NFS packets have arrived.  More precisely, this
+	is the number of times that the network stack has notified the
+	sunrpc server layer that new data may be available on a transport
+	(e.g. an NFS or UDP socket or an NFS/RDMA endpoint).
+
+	Depending on the NFS workload patterns and various network stack
+	effects (such as Large Receive Offload) which can combine packets
+	on the wire, this may be either more or less than the number
+	of NFS calls received (which statistic is available elsewhere).
+	However this is a more accurate and less workload-dependent measure
+	of how much CPU load is being placed on the sunrpc server layer
+	due to NFS network traffic.
+
+sockets-enqueued
+	Counts how many times an NFS transport is enqueued to wait for
+	an nfsd thread to service it, i.e. no nfsd thread was considered
+	available.
+
+	The circumstance this statistic tracks indicates that there was NFS
+	network-facing work to be done but it couldn't be done immediately,
+	thus introducing a small delay in servicing NFS calls.  The ideal
+	rate of change for this counter is zero; significantly non-zero
+	values may indicate a performance limitation.
+
+	This can happen because there are too few nfsd threads in the thread
+	pool for the NFS workload (the workload is thread-limited), in which
+	case configuring more nfsd threads will probably improve the
+	performance of the NFS workload.
+
+threads-woken
+	Counts how many times an idle nfsd thread is woken to try to
+	receive some data from an NFS transport.
+
+	This statistic tracks the circumstance where incoming
+	network-facing NFS work is being handled quickly, which is a good
+	thing.  The ideal rate of change for this counter will be close
+	to but less than the rate of change of the packets-arrived counter.
+
+threads-timedout
+	Counts how many times an nfsd thread triggered an idle timeout,
+	i.e. was not woken to handle any incoming network packets for
+	some time.
+
+	This statistic counts a circumstance where there are more nfsd
+	threads configured than can be used by the NFS workload.  This is
+	a clue that the number of nfsd threads can be reduced without
+	affecting performance.  Unfortunately, it's only a clue and not
+	a strong indication, for a couple of reasons:
+
+	 - Currently the rate at which the counter is incremented is quite
+	   slow; the idle timeout is 60 minutes.  Unless the NFS workload
+	   remains constant for hours at a time, this counter is unlikely
+	   to be providing information that is still useful.
+
+	 - It is usually a wise policy to provide some slack,
+	   i.e. configure a few more nfsds than are currently needed,
+	   to allow for future spikes in load.
+
+
+Note that incoming packets on NFS transports will be dealt with in
+one of three ways.  An nfsd thread can be woken (threads-woken counts
+this case), or the transport can be enqueued for later attention
+(sockets-enqueued counts this case), or the packet can be temporarily
+deferred because the transport is currently being used by an nfsd
+thread.  This last case is not very interesting and is not explicitly
+counted, but can be inferred from the other counters thus:
+
+packets-deferred = packets-arrived - ( sockets-enqueued + threads-woken )
+
+
+More
+----
+Descriptions of the other statistics file should go here.
+
+
+Greg Banks <gnb@sgi.com>
+26 Mar 2009
diff --git a/Documentation/filesystems/nfs/nfs-rdma.txt b/Documentation/filesystems/nfs/nfs-rdma.txt
new file mode 100644
index 0000000..22dc0dd
--- /dev/null
+++ b/Documentation/filesystems/nfs/nfs-rdma.txt
@@ -0,0 +1,274 @@
+################################################################################
+#									       #
+#				NFS/RDMA README				       #
+#									       #
+################################################################################
+
+ Author: NetApp and Open Grid Computing
+ Date: May 29, 2008
+
+Table of Contents
+~~~~~~~~~~~~~~~~~
+ - Overview
+ - Getting Help
+ - Installation
+ - Check RDMA and NFS Setup
+ - NFS/RDMA Setup
+
+Overview
+~~~~~~~~
+
+  This document describes how to install and setup the Linux NFS/RDMA client
+  and server software.
+
+  The NFS/RDMA client was first included in Linux 2.6.24. The NFS/RDMA server
+  was first included in the following release, Linux 2.6.25.
+
+  In our testing, we have obtained excellent performance results (full 10Gbit
+  wire bandwidth at minimal client CPU) under many workloads. The code passes
+  the full Connectathon test suite and operates over both Infiniband and iWARP
+  RDMA adapters.
+
+Getting Help
+~~~~~~~~~~~~
+
+  If you get stuck, you can ask questions on the
+
+                nfs-rdma-devel@lists.sourceforge.net
+
+  mailing list.
+
+Installation
+~~~~~~~~~~~~
+
+  These instructions are a step by step guide to building a machine for
+  use with NFS/RDMA.
+
+  - Install an RDMA device
+
+    Any device supported by the drivers in drivers/infiniband/hw is acceptable.
+
+    Testing has been performed using several Mellanox-based IB cards, the
+    Ammasso AMS1100 iWARP adapter, and the Chelsio cxgb3 iWARP adapter.
+
+  - Install a Linux distribution and tools
+
+    The first kernel release to contain both the NFS/RDMA client and server was
+    Linux 2.6.25  Therefore, a distribution compatible with this and subsequent
+    Linux kernel release should be installed.
+
+    The procedures described in this document have been tested with
+    distributions from Red Hat's Fedora Project (http://fedora.redhat.com/).
+
+  - Install nfs-utils-1.1.2 or greater on the client
+
+    An NFS/RDMA mount point can be obtained by using the mount.nfs command in
+    nfs-utils-1.1.2 or greater (nfs-utils-1.1.1 was the first nfs-utils
+    version with support for NFS/RDMA mounts, but for various reasons we
+    recommend using nfs-utils-1.1.2 or greater). To see which version of
+    mount.nfs you are using, type:
+
+    $ /sbin/mount.nfs -V
+
+    If the version is less than 1.1.2 or the command does not exist,
+    you should install the latest version of nfs-utils.
+
+    Download the latest package from:
+
+    http://www.kernel.org/pub/linux/utils/nfs
+
+    Uncompress the package and follow the installation instructions.
+
+    If you will not need the idmapper and gssd executables (you do not need
+    these to create an NFS/RDMA enabled mount command), the installation
+    process can be simplified by disabling these features when running
+    configure:
+
+    $ ./configure --disable-gss --disable-nfsv4
+
+    To build nfs-utils you will need the tcp_wrappers package installed. For
+    more information on this see the package's README and INSTALL files.
+
+    After building the nfs-utils package, there will be a mount.nfs binary in
+    the utils/mount directory. This binary can be used to initiate NFS v2, v3,
+    or v4 mounts. To initiate a v4 mount, the binary must be called
+    mount.nfs4.  The standard technique is to create a symlink called
+    mount.nfs4 to mount.nfs.
+
+    This mount.nfs binary should be installed at /sbin/mount.nfs as follows:
+
+    $ sudo cp utils/mount/mount.nfs /sbin/mount.nfs
+
+    In this location, mount.nfs will be invoked automatically for NFS mounts
+    by the system mount command.
+
+    NOTE: mount.nfs and therefore nfs-utils-1.1.2 or greater is only needed
+    on the NFS client machine. You do not need this specific version of
+    nfs-utils on the server. Furthermore, only the mount.nfs command from
+    nfs-utils-1.1.2 is needed on the client.
+
+  - Install a Linux kernel with NFS/RDMA
+
+    The NFS/RDMA client and server are both included in the mainline Linux
+    kernel version 2.6.25 and later. This and other versions of the Linux
+    kernel can be found at:
+
+    https://www.kernel.org/pub/linux/kernel/
+
+    Download the sources and place them in an appropriate location.
+
+  - Configure the RDMA stack
+
+    Make sure your kernel configuration has RDMA support enabled. Under
+    Device Drivers -> InfiniBand support, update the kernel configuration
+    to enable InfiniBand support [NOTE: the option name is misleading. Enabling
+    InfiniBand support is required for all RDMA devices (IB, iWARP, etc.)].
+
+    Enable the appropriate IB HCA support (mlx4, mthca, ehca, ipath, etc.) or
+    iWARP adapter support (amso, cxgb3, etc.).
+
+    If you are using InfiniBand, be sure to enable IP-over-InfiniBand support.
+
+  - Configure the NFS client and server
+
+    Your kernel configuration must also have NFS file system support and/or
+    NFS server support enabled. These and other NFS related configuration
+    options can be found under File Systems -> Network File Systems.
+
+  - Build, install, reboot
+
+    The NFS/RDMA code will be enabled automatically if NFS and RDMA
+    are turned on. The NFS/RDMA client and server are configured via the hidden
+    SUNRPC_XPRT_RDMA config option that depends on SUNRPC and INFINIBAND. The
+    value of SUNRPC_XPRT_RDMA will be:
+
+     - N if either SUNRPC or INFINIBAND are N, in this case the NFS/RDMA client
+       and server will not be built
+     - M if both SUNRPC and INFINIBAND are on (M or Y) and at least one is M,
+       in this case the NFS/RDMA client and server will be built as modules
+     - Y if both SUNRPC and INFINIBAND are Y, in this case the NFS/RDMA client
+       and server will be built into the kernel
+
+    Therefore, if you have followed the steps above and turned no NFS and RDMA,
+    the NFS/RDMA client and server will be built.
+
+    Build a new kernel, install it, boot it.
+
+Check RDMA and NFS Setup
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+    Before configuring the NFS/RDMA software, it is a good idea to test
+    your new kernel to ensure that the kernel is working correctly.
+    In particular, it is a good idea to verify that the RDMA stack
+    is functioning as expected and standard NFS over TCP/IP and/or UDP/IP
+    is working properly.
+
+  - Check RDMA Setup
+
+    If you built the RDMA components as modules, load them at
+    this time. For example, if you are using a Mellanox Tavor/Sinai/Arbel
+    card:
+
+    $ modprobe ib_mthca
+    $ modprobe ib_ipoib
+
+    If you are using InfiniBand, make sure there is a Subnet Manager (SM)
+    running on the network. If your IB switch has an embedded SM, you can
+    use it. Otherwise, you will need to run an SM, such as OpenSM, on one
+    of your end nodes.
+
+    If an SM is running on your network, you should see the following:
+
+    $ cat /sys/class/infiniband/driverX/ports/1/state
+    4: ACTIVE
+
+    where driverX is mthca0, ipath5, ehca3, etc.
+
+    To further test the InfiniBand software stack, use IPoIB (this
+    assumes you have two IB hosts named host1 and host2):
+
+    host1$ ip link set dev ib0 up
+    host1$ ip address add dev ib0 a.b.c.x
+    host2$ ip link set dev ib0 up
+    host2$ ip address add dev ib0 a.b.c.y
+    host1$ ping a.b.c.y
+    host2$ ping a.b.c.x
+
+    For other device types, follow the appropriate procedures.
+
+  - Check NFS Setup
+
+    For the NFS components enabled above (client and/or server),
+    test their functionality over standard Ethernet using TCP/IP or UDP/IP.
+
+NFS/RDMA Setup
+~~~~~~~~~~~~~~
+
+  We recommend that you use two machines, one to act as the client and
+  one to act as the server.
+
+  One time configuration:
+
+  - On the server system, configure the /etc/exports file and
+    start the NFS/RDMA server.
+
+    Exports entries with the following formats have been tested:
+
+    /vol0   192.168.0.47(fsid=0,rw,async,insecure,no_root_squash)
+    /vol0   192.168.0.0/255.255.255.0(fsid=0,rw,async,insecure,no_root_squash)
+
+    The IP address(es) is(are) the client's IPoIB address for an InfiniBand
+    HCA or the client's iWARP address(es) for an RNIC.
+
+    NOTE: The "insecure" option must be used because the NFS/RDMA client does
+    not use a reserved port.
+
+ Each time a machine boots:
+
+  - Load and configure the RDMA drivers
+
+    For InfiniBand using a Mellanox adapter:
+
+    $ modprobe ib_mthca
+    $ modprobe ib_ipoib
+    $ ip li set dev ib0 up
+    $ ip addr add dev ib0 a.b.c.d
+
+    NOTE: use unique addresses for the client and server
+
+  - Start the NFS server
+
+    If the NFS/RDMA server was built as a module (CONFIG_SUNRPC_XPRT_RDMA=m in
+    kernel config), load the RDMA transport module:
+
+    $ modprobe svcrdma
+
+    Regardless of how the server was built (module or built-in), start the
+    server:
+
+    $ /etc/init.d/nfs start
+
+    or
+
+    $ service nfs start
+
+    Instruct the server to listen on the RDMA transport:
+
+    $ echo rdma 20049 > /proc/fs/nfsd/portlist
+
+  - On the client system
+
+    If the NFS/RDMA client was built as a module (CONFIG_SUNRPC_XPRT_RDMA=m in
+    kernel config), load the RDMA client module:
+
+    $ modprobe xprtrdma.ko
+
+    Regardless of how the client was built (module or built-in), use this
+    command to mount the NFS/RDMA server:
+
+    $ mount -o rdma,port=20049 <IPoIB-server-name-or-address>:/<export> /mnt
+
+    To verify that the mount is using RDMA, run "cat /proc/mounts" and check
+    the "proto" field for the given mount.
+
+  Congratulations! You're using NFS/RDMA!
diff --git a/Documentation/filesystems/nfs/nfs.txt b/Documentation/filesystems/nfs/nfs.txt
new file mode 100644
index 0000000..f2571c8
--- /dev/null
+++ b/Documentation/filesystems/nfs/nfs.txt
@@ -0,0 +1,136 @@
+
+The NFS client
+==============
+
+The NFS version 2 protocol was first documented in RFC1094 (March 1989).
+Since then two more major releases of NFS have been published, with NFSv3
+being documented in RFC1813 (June 1995), and NFSv4 in RFC3530 (April
+2003).
+
+The Linux NFS client currently supports all the above published versions,
+and work is in progress on adding support for minor version 1 of the NFSv4
+protocol.
+
+The purpose of this document is to provide information on some of the
+special features of the NFS client that can be configured by system
+administrators.
+
+
+The nfs4_unique_id parameter
+============================
+
+NFSv4 requires clients to identify themselves to servers with a unique
+string.  File open and lock state shared between one client and one server
+is associated with this identity.  To support robust NFSv4 state recovery
+and transparent state migration, this identity string must not change
+across client reboots.
+
+Without any other intervention, the Linux client uses a string that contains
+the local system's node name.  System administrators, however, often do not
+take care to ensure that node names are fully qualified and do not change
+over the lifetime of a client system.  Node names can have other
+administrative requirements that require particular behavior that does not
+work well as part of an nfs_client_id4 string.
+
+The nfs.nfs4_unique_id boot parameter specifies a unique string that can be
+used instead of a system's node name when an NFS client identifies itself to
+a server.  Thus, if the system's node name is not unique, or it changes, its
+nfs.nfs4_unique_id stays the same, preventing collision with other clients
+or loss of state during NFS reboot recovery or transparent state migration.
+
+The nfs.nfs4_unique_id string is typically a UUID, though it can contain
+anything that is believed to be unique across all NFS clients.  An
+nfs4_unique_id string should be chosen when a client system is installed,
+just as a system's root file system gets a fresh UUID in its label at
+install time.
+
+The string should remain fixed for the lifetime of the client.  It can be
+changed safely if care is taken that the client shuts down cleanly and all
+outstanding NFSv4 state has expired, to prevent loss of NFSv4 state.
+
+This string can be stored in an NFS client's grub.conf, or it can be provided
+via a net boot facility such as PXE.  It may also be specified as an nfs.ko
+module parameter.  Specifying a uniquifier string is not support for NFS
+clients running in containers.
+
+
+The DNS resolver
+================
+
+NFSv4 allows for one server to refer the NFS client to data that has been
+migrated onto another server by means of the special "fs_locations"
+attribute. See
+	http://tools.ietf.org/html/rfc3530#section-6
+and
+	http://tools.ietf.org/html/draft-ietf-nfsv4-referrals-00
+
+The fs_locations information can take the form of either an ip address and
+a path, or a DNS hostname and a path. The latter requires the NFS client to
+do a DNS lookup in order to mount the new volume, and hence the need for an
+upcall to allow userland to provide this service.
+
+Assuming that the user has the 'rpc_pipefs' filesystem mounted in the usual
+/var/lib/nfs/rpc_pipefs, the upcall consists of the following steps:
+
+   (1) The process checks the dns_resolve cache to see if it contains a
+       valid entry. If so, it returns that entry and exits.
+
+   (2) If no valid entry exists, the helper script '/sbin/nfs_cache_getent'
+       (may be changed using the 'nfs.cache_getent' kernel boot parameter)
+       is run, with two arguments:
+		- the cache name, "dns_resolve"
+		- the hostname to resolve
+
+   (3) After looking up the corresponding ip address, the helper script
+       writes the result into the rpc_pipefs pseudo-file
+       '/var/lib/nfs/rpc_pipefs/cache/dns_resolve/channel'
+       in the following (text) format:
+
+		"<ip address> <hostname> <ttl>\n"
+
+       Where <ip address> is in the usual IPv4 (123.456.78.90) or IPv6
+       (ffee:ddcc:bbaa:9988:7766:5544:3322:1100, ffee::1100, ...) format.
+       <hostname> is identical to the second argument of the helper
+       script, and <ttl> is the 'time to live' of this cache entry (in
+       units of seconds).
+
+       Note: If <ip address> is invalid, say the string "0", then a negative
+       entry is created, which will cause the kernel to treat the hostname
+       as having no valid DNS translation.
+
+
+
+
+A basic sample /sbin/nfs_cache_getent
+=====================================
+
+#!/bin/bash
+#
+ttl=600
+#
+cut=/usr/bin/cut
+getent=/usr/bin/getent
+rpc_pipefs=/var/lib/nfs/rpc_pipefs
+#
+die()
+{
+	echo "Usage: $0 cache_name entry_name"
+	exit 1
+}
+
+[ $# -lt 2 ] && die
+cachename="$1"
+cache_path=${rpc_pipefs}/cache/${cachename}/channel
+
+case "${cachename}" in
+	dns_resolve)
+		name="$2"
+		result="$(${getent} hosts ${name} | ${cut} -f1 -d\ )"
+		[ -z "${result}" ] && result="0"
+		;;
+	*)
+		die
+		;;
+esac
+echo "${result} ${name} ${ttl}" >${cache_path}
+
diff --git a/Documentation/filesystems/nfs/nfs41-server.txt b/Documentation/filesystems/nfs/nfs41-server.txt
new file mode 100644
index 0000000..682a59f
--- /dev/null
+++ b/Documentation/filesystems/nfs/nfs41-server.txt
@@ -0,0 +1,173 @@
+NFSv4.1 Server Implementation
+
+Server support for minorversion 1 can be controlled using the
+/proc/fs/nfsd/versions control file.  The string output returned
+by reading this file will contain either "+4.1" or "-4.1"
+correspondingly.
+
+Currently, server support for minorversion 1 is enabled by default.
+It can be disabled at run time by writing the string "-4.1" to
+the /proc/fs/nfsd/versions control file.  Note that to write this
+control file, the nfsd service must be taken down.  You can use rpc.nfsd
+for this; see rpc.nfsd(8).
+
+(Warning: older servers will interpret "+4.1" and "-4.1" as "+4" and
+"-4", respectively.  Therefore, code meant to work on both new and old
+kernels must turn 4.1 on or off *before* turning support for version 4
+on or off; rpc.nfsd does this correctly.)
+
+The NFSv4 minorversion 1 (NFSv4.1) implementation in nfsd is based
+on RFC 5661.
+
+From the many new features in NFSv4.1 the current implementation
+focuses on the mandatory-to-implement NFSv4.1 Sessions, providing
+"exactly once" semantics and better control and throttling of the
+resources allocated for each client.
+
+The table below, taken from the NFSv4.1 document, lists
+the operations that are mandatory to implement (REQ), optional
+(OPT), and NFSv4.0 operations that are required not to implement (MNI)
+in minor version 1.  The first column indicates the operations that
+are not supported yet by the linux server implementation.
+
+The OPTIONAL features identified and their abbreviations are as follows:
+	pNFS	Parallel NFS
+	FDELG	File Delegations
+	DDELG	Directory Delegations
+
+The following abbreviations indicate the linux server implementation status.
+	I	Implemented NFSv4.1 operations.
+	NS	Not Supported.
+	NS*	Unimplemented optional feature.
+
+Operations
+
+   +----------------------+------------+--------------+----------------+
+   | Operation            | REQ, REC,  | Feature      | Definition     |
+   |                      | OPT, or    | (REQ, REC,   |                |
+   |                      | MNI        | or OPT)      |                |
+   +----------------------+------------+--------------+----------------+
+   | ACCESS               | REQ        |              | Section 18.1   |
+I  | BACKCHANNEL_CTL      | REQ        |              | Section 18.33  |
+I  | BIND_CONN_TO_SESSION | REQ        |              | Section 18.34  |
+   | CLOSE                | REQ        |              | Section 18.2   |
+   | COMMIT               | REQ        |              | Section 18.3   |
+   | CREATE               | REQ        |              | Section 18.4   |
+I  | CREATE_SESSION       | REQ        |              | Section 18.36  |
+NS*| DELEGPURGE           | OPT        | FDELG (REQ)  | Section 18.5   |
+   | DELEGRETURN          | OPT        | FDELG,       | Section 18.6   |
+   |                      |            | DDELG, pNFS  |                |
+   |                      |            | (REQ)        |                |
+I  | DESTROY_CLIENTID     | REQ        |              | Section 18.50  |
+I  | DESTROY_SESSION      | REQ        |              | Section 18.37  |
+I  | EXCHANGE_ID          | REQ        |              | Section 18.35  |
+I  | FREE_STATEID         | REQ        |              | Section 18.38  |
+   | GETATTR              | REQ        |              | Section 18.7   |
+I  | GETDEVICEINFO        | OPT        | pNFS (REQ)   | Section 18.40  |
+NS*| GETDEVICELIST        | OPT        | pNFS (OPT)   | Section 18.41  |
+   | GETFH                | REQ        |              | Section 18.8   |
+NS*| GET_DIR_DELEGATION   | OPT        | DDELG (REQ)  | Section 18.39  |
+I  | LAYOUTCOMMIT         | OPT        | pNFS (REQ)   | Section 18.42  |
+I  | LAYOUTGET            | OPT        | pNFS (REQ)   | Section 18.43  |
+I  | LAYOUTRETURN         | OPT        | pNFS (REQ)   | Section 18.44  |
+   | LINK                 | OPT        |              | Section 18.9   |
+   | LOCK                 | REQ        |              | Section 18.10  |
+   | LOCKT                | REQ        |              | Section 18.11  |
+   | LOCKU                | REQ        |              | Section 18.12  |
+   | LOOKUP               | REQ        |              | Section 18.13  |
+   | LOOKUPP              | REQ        |              | Section 18.14  |
+   | NVERIFY              | REQ        |              | Section 18.15  |
+   | OPEN                 | REQ        |              | Section 18.16  |
+NS*| OPENATTR             | OPT        |              | Section 18.17  |
+   | OPEN_CONFIRM         | MNI        |              | N/A            |
+   | OPEN_DOWNGRADE       | REQ        |              | Section 18.18  |
+   | PUTFH                | REQ        |              | Section 18.19  |
+   | PUTPUBFH             | REQ        |              | Section 18.20  |
+   | PUTROOTFH            | REQ        |              | Section 18.21  |
+   | READ                 | REQ        |              | Section 18.22  |
+   | READDIR              | REQ        |              | Section 18.23  |
+   | READLINK             | OPT        |              | Section 18.24  |
+   | RECLAIM_COMPLETE     | REQ        |              | Section 18.51  |
+   | RELEASE_LOCKOWNER    | MNI        |              | N/A            |
+   | REMOVE               | REQ        |              | Section 18.25  |
+   | RENAME               | REQ        |              | Section 18.26  |
+   | RENEW                | MNI        |              | N/A            |
+   | RESTOREFH            | REQ        |              | Section 18.27  |
+   | SAVEFH               | REQ        |              | Section 18.28  |
+   | SECINFO              | REQ        |              | Section 18.29  |
+I  | SECINFO_NO_NAME      | REC        | pNFS files   | Section 18.45, |
+   |                      |            | layout (REQ) | Section 13.12  |
+I  | SEQUENCE             | REQ        |              | Section 18.46  |
+   | SETATTR              | REQ        |              | Section 18.30  |
+   | SETCLIENTID          | MNI        |              | N/A            |
+   | SETCLIENTID_CONFIRM  | MNI        |              | N/A            |
+NS | SET_SSV              | REQ        |              | Section 18.47  |
+I  | TEST_STATEID         | REQ        |              | Section 18.48  |
+   | VERIFY               | REQ        |              | Section 18.31  |
+NS*| WANT_DELEGATION      | OPT        | FDELG (OPT)  | Section 18.49  |
+   | WRITE                | REQ        |              | Section 18.32  |
+
+Callback Operations
+
+   +-------------------------+-----------+-------------+---------------+
+   | Operation               | REQ, REC, | Feature     | Definition    |
+   |                         | OPT, or   | (REQ, REC,  |               |
+   |                         | MNI       | or OPT)     |               |
+   +-------------------------+-----------+-------------+---------------+
+   | CB_GETATTR              | OPT       | FDELG (REQ) | Section 20.1  |
+I  | CB_LAYOUTRECALL         | OPT       | pNFS (REQ)  | Section 20.3  |
+NS*| CB_NOTIFY               | OPT       | DDELG (REQ) | Section 20.4  |
+NS*| CB_NOTIFY_DEVICEID      | OPT       | pNFS (OPT)  | Section 20.12 |
+NS*| CB_NOTIFY_LOCK          | OPT       |             | Section 20.11 |
+NS*| CB_PUSH_DELEG           | OPT       | FDELG (OPT) | Section 20.5  |
+   | CB_RECALL               | OPT       | FDELG,      | Section 20.2  |
+   |                         |           | DDELG, pNFS |               |
+   |                         |           | (REQ)       |               |
+NS*| CB_RECALL_ANY           | OPT       | FDELG,      | Section 20.6  |
+   |                         |           | DDELG, pNFS |               |
+   |                         |           | (REQ)       |               |
+NS | CB_RECALL_SLOT          | REQ       |             | Section 20.8  |
+NS*| CB_RECALLABLE_OBJ_AVAIL | OPT       | DDELG, pNFS | Section 20.7  |
+   |                         |           | (REQ)       |               |
+I  | CB_SEQUENCE             | OPT       | FDELG,      | Section 20.9  |
+   |                         |           | DDELG, pNFS |               |
+   |                         |           | (REQ)       |               |
+NS*| CB_WANTS_CANCELLED      | OPT       | FDELG,      | Section 20.10 |
+   |                         |           | DDELG, pNFS |               |
+   |                         |           | (REQ)       |               |
+   +-------------------------+-----------+-------------+---------------+
+
+Implementation notes:
+
+SSV:
+* The spec claims this is mandatory, but we don't actually know of any
+  implementations, so we're ignoring it for now.  The server returns
+  NFS4ERR_ENCR_ALG_UNSUPP on EXCHANGE_ID, which should be future-proof.
+
+GSS on the backchannel:
+* Again, theoretically required but not widely implemented (in
+  particular, the current Linux client doesn't request it).  We return
+  NFS4ERR_ENCR_ALG_UNSUPP on CREATE_SESSION.
+
+DELEGPURGE:
+* mandatory only for servers that support CLAIM_DELEGATE_PREV and/or
+  CLAIM_DELEG_PREV_FH (which allows clients to keep delegations that
+  persist across client reboots).  Thus we need not implement this for
+  now.
+
+EXCHANGE_ID:
+* implementation ids are ignored
+
+CREATE_SESSION:
+* backchannel attributes are ignored
+
+SEQUENCE:
+* no support for dynamic slot table renegotiation (optional)
+
+Nonstandard compound limitations:
+* No support for a sessions fore channel RPC compound that requires both a
+  ca_maxrequestsize request and a ca_maxresponsesize reply, so we may
+  fail to live up to the promise we made in CREATE_SESSION fore channel
+  negotiation.
+
+See also http://wiki.linux-nfs.org/wiki/index.php/Server_4.0_and_4.1_issues.
diff --git a/Documentation/filesystems/nfs/nfsd-admin-interfaces.txt b/Documentation/filesystems/nfs/nfsd-admin-interfaces.txt
new file mode 100644
index 0000000..56a96fb
--- /dev/null
+++ b/Documentation/filesystems/nfs/nfsd-admin-interfaces.txt
@@ -0,0 +1,41 @@
+Administrative interfaces for nfsd
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Note that normally these interfaces are used only by the utilities in
+nfs-utils.
+
+nfsd is controlled mainly by pseudofiles under the "nfsd" filesystem,
+which is normally mounted at /proc/fs/nfsd/.
+
+The server is always started by the first write of a nonzero value to
+nfsd/threads.
+
+Before doing that, NFSD can be told which sockets to listen on by
+writing to nfsd/portlist; that write may be:
+
+	- an ascii-encoded file descriptor, which should refer to a
+	  bound (and listening, for tcp) socket, or
+	- "transportname port", where transportname is currently either
+	  "udp", "tcp", or "rdma".
+
+If nfsd is started without doing any of these, then it will create one
+udp and one tcp listener at port 2049 (see nfsd_init_socks).
+
+On startup, nfsd and lockd grace periods start.
+
+nfsd is shut down by a write of 0 to nfsd/threads.  All locks and state
+are thrown away at that point.
+
+Between startup and shutdown, the number of threads may be adjusted up
+or down by additional writes to nfsd/threads or by writes to
+nfsd/pool_threads.
+
+For more detail about files under nfsd/ and what they control, see
+fs/nfsd/nfsctl.c; most of them have detailed comments.
+
+Implementation notes
+^^^^^^^^^^^^^^^^^^^^
+
+Note that the rpc server requires the caller to serialize addition and
+removal of listening sockets, and startup and shutdown of the server.
+For nfsd this is done using nfsd_mutex.
diff --git a/Documentation/filesystems/nfs/nfsroot.txt b/Documentation/filesystems/nfs/nfsroot.txt
new file mode 100644
index 0000000..d296312
--- /dev/null
+++ b/Documentation/filesystems/nfs/nfsroot.txt
@@ -0,0 +1,355 @@
+Mounting the root filesystem via NFS (nfsroot)
+===============================================
+
+Written 1996 by Gero Kuhlmann <gero@gkminix.han.de>
+Updated 1997 by Martin Mares <mj@atrey.karlin.mff.cuni.cz>
+Updated 2006 by Nico Schottelius <nico-kernel-nfsroot@schottelius.org>
+Updated 2006 by Horms <horms@verge.net.au>
+Updated 2018 by Chris Novakovic <chris@chrisn.me.uk>
+
+
+
+In order to use a diskless system, such as an X-terminal or printer server
+for example, it is necessary for the root filesystem to be present on a
+non-disk device. This may be an initramfs (see Documentation/filesystems/
+ramfs-rootfs-initramfs.txt), a ramdisk (see Documentation/admin-guide/initrd.rst) or a
+filesystem mounted via NFS. The following text describes on how to use NFS
+for the root filesystem. For the rest of this text 'client' means the
+diskless system, and 'server' means the NFS server.
+
+
+
+
+1.) Enabling nfsroot capabilities
+    -----------------------------
+
+In order to use nfsroot, NFS client support needs to be selected as
+built-in during configuration. Once this has been selected, the nfsroot
+option will become available, which should also be selected.
+
+In the networking options, kernel level autoconfiguration can be selected,
+along with the types of autoconfiguration to support. Selecting all of
+DHCP, BOOTP and RARP is safe.
+
+
+
+
+2.) Kernel command line
+    -------------------
+
+When the kernel has been loaded by a boot loader (see below) it needs to be
+told what root fs device to use. And in the case of nfsroot, where to find
+both the server and the name of the directory on the server to mount as root.
+This can be established using the following kernel command line parameters:
+
+
+root=/dev/nfs
+
+  This is necessary to enable the pseudo-NFS-device. Note that it's not a
+  real device but just a synonym to tell the kernel to use NFS instead of
+  a real device.
+
+
+nfsroot=[<server-ip>:]<root-dir>[,<nfs-options>]
+
+  If the `nfsroot' parameter is NOT given on the command line,
+  the default "/tftpboot/%s" will be used.
+
+  <server-ip>	Specifies the IP address of the NFS server.
+		The default address is determined by the `ip' parameter
+		(see below). This parameter allows the use of different
+		servers for IP autoconfiguration and NFS.
+
+  <root-dir>	Name of the directory on the server to mount as root.
+		If there is a "%s" token in the string, it will be
+		replaced by the ASCII-representation of the client's
+		IP address.
+
+  <nfs-options>	Standard NFS options. All options are separated by commas.
+		The following defaults are used:
+			port		= as given by server portmap daemon
+			rsize		= 4096
+			wsize		= 4096
+			timeo		= 7
+			retrans		= 3
+			acregmin	= 3
+			acregmax	= 60
+			acdirmin	= 30
+			acdirmax	= 60
+			flags		= hard, nointr, noposix, cto, ac
+
+
+ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>:
+   <dns0-ip>:<dns1-ip>:<ntp0-ip>
+
+  This parameter tells the kernel how to configure IP addresses of devices
+  and also how to set up the IP routing table. It was originally called
+  `nfsaddrs', but now the boot-time IP configuration works independently of
+  NFS, so it was renamed to `ip' and the old name remained as an alias for
+  compatibility reasons.
+
+  If this parameter is missing from the kernel command line, all fields are
+  assumed to be empty, and the defaults mentioned below apply. In general
+  this means that the kernel tries to configure everything using
+  autoconfiguration.
+
+  The <autoconf> parameter can appear alone as the value to the `ip'
+  parameter (without all the ':' characters before).  If the value is
+  "ip=off" or "ip=none", no autoconfiguration will take place, otherwise
+  autoconfiguration will take place.  The most common way to use this
+  is "ip=dhcp".
+
+  <client-ip>	IP address of the client.
+
+  		Default:  Determined using autoconfiguration.
+
+  <server-ip>	IP address of the NFS server. If RARP is used to determine
+		the client address and this parameter is NOT empty only
+		replies from the specified server are accepted.
+
+		Only required for NFS root. That is autoconfiguration
+		will not be triggered if it is missing and NFS root is not
+		in operation.
+
+		Value is exported to /proc/net/pnp with the prefix "bootserver "
+		(see below).
+
+		Default: Determined using autoconfiguration.
+		         The address of the autoconfiguration server is used.
+
+  <gw-ip>	IP address of a gateway if the server is on a different subnet.
+
+		Default: Determined using autoconfiguration.
+
+  <netmask>	Netmask for local network interface. If unspecified
+		the netmask is derived from the client IP address assuming
+		classful addressing.
+
+		Default:  Determined using autoconfiguration.
+
+  <hostname>	Name of the client. If a '.' character is present, anything
+		before the first '.' is used as the client's hostname, and anything
+		after it is used as its NIS domain name. May be supplied by
+		autoconfiguration, but its absence will not trigger autoconfiguration.
+		If specified and DHCP is used, the user-provided hostname (and NIS
+		domain name, if present) will be carried in the DHCP request; this
+		may cause a DNS record to be created or updated for the client.
+
+  		Default: Client IP address is used in ASCII notation.
+
+  <device>	Name of network device to use.
+
+		Default: If the host only has one device, it is used.
+			 Otherwise the device is determined using
+			 autoconfiguration. This is done by sending
+			 autoconfiguration requests out of all devices,
+			 and using the device that received the first reply.
+
+  <autoconf>	Method to use for autoconfiguration. In the case of options
+                which specify multiple autoconfiguration protocols,
+		requests are sent using all protocols, and the first one
+		to reply is used.
+
+		Only autoconfiguration protocols that have been compiled
+		into the kernel will be used, regardless of the value of
+		this option.
+
+                  off or none: don't use autoconfiguration
+				(do static IP assignment instead)
+		  on or any:   use any protocol available in the kernel
+			       (default)
+		  dhcp:        use DHCP
+		  bootp:       use BOOTP
+		  rarp:        use RARP
+		  both:        use both BOOTP and RARP but not DHCP
+		               (old option kept for backwards compatibility)
+
+		if dhcp is used, the client identifier can be used by following
+		format "ip=dhcp,client-id-type,client-id-value"
+
+                Default: any
+
+  <dns0-ip>	IP address of primary nameserver.
+		Value is exported to /proc/net/pnp with the prefix "nameserver "
+		(see below).
+
+		Default: None if not using autoconfiguration; determined
+		automatically if using autoconfiguration.
+
+  <dns1-ip>	IP address of secondary nameserver.
+		See <dns0-ip>.
+
+  <ntp0-ip>	IP address of a Network Time Protocol (NTP) server.
+		Value is exported to /proc/net/ipconfig/ntp_servers, but is
+		otherwise unused (see below).
+
+		Default: None if not using autoconfiguration; determined
+		automatically if using autoconfiguration.
+
+  After configuration (whether manual or automatic) is complete, two files
+  are created in the following format; lines are omitted if their respective
+  value is empty following configuration:
+
+  - /proc/net/pnp:
+
+	#PROTO: <DHCP|BOOTP|RARP|MANUAL>	(depending on configuration method)
+	domain <dns-domain>			(if autoconfigured, the DNS domain)
+	nameserver <dns0-ip>			(primary name server IP)
+	nameserver <dns1-ip>			(secondary name server IP)
+	nameserver <dns2-ip>			(tertiary name server IP)
+	bootserver <server-ip>			(NFS server IP)
+
+  - /proc/net/ipconfig/ntp_servers:
+
+	<ntp0-ip>				(NTP server IP)
+	<ntp1-ip>				(NTP server IP)
+	<ntp2-ip>				(NTP server IP)
+
+  <dns-domain> and <dns2-ip> (in /proc/net/pnp) and <ntp1-ip> and <ntp2-ip>
+  (in /proc/net/ipconfig/ntp_servers) are requested during autoconfiguration;
+  they cannot be specified as part of the "ip=" kernel command line parameter.
+
+  Because the "domain" and "nameserver" options are recognised by DNS
+  resolvers, /etc/resolv.conf is often linked to /proc/net/pnp on systems
+  that use an NFS root filesystem.
+
+  Note that the kernel will not synchronise the system time with any NTP
+  servers it discovers; this is the responsibility of a user space process
+  (e.g. an initrd/initramfs script that passes the IP addresses listed in
+  /proc/net/ipconfig/ntp_servers to an NTP client before mounting the real
+  root filesystem if it is on NFS).
+
+
+nfsrootdebug
+
+  This parameter enables debugging messages to appear in the kernel
+  log at boot time so that administrators can verify that the correct
+  NFS mount options, server address, and root path are passed to the
+  NFS client.
+
+
+rdinit=<executable file>
+
+  To specify which file contains the program that starts system
+  initialization, administrators can use this command line parameter.
+  The default value of this parameter is "/init".  If the specified
+  file exists and the kernel can execute it, root filesystem related
+  kernel command line parameters, including `nfsroot=', are ignored.
+
+  A description of the process of mounting the root file system can be
+  found in:
+
+    Documentation/early-userspace/README
+
+
+
+
+3.) Boot Loader
+    ----------
+
+To get the kernel into memory different approaches can be used.
+They depend on various facilities being available:
+
+
+3.1)  Booting from a floppy using syslinux
+
+	When building kernels, an easy way to create a boot floppy that uses
+	syslinux is to use the zdisk or bzdisk make targets which use zimage
+      	and bzimage images respectively. Both targets accept the
+     	FDARGS parameter which can be used to set the kernel command line.
+
+	e.g.
+	   make bzdisk FDARGS="root=/dev/nfs"
+
+   	Note that the user running this command will need to have
+     	access to the floppy drive device, /dev/fd0
+
+     	For more information on syslinux, including how to create bootdisks
+     	for prebuilt kernels, see http://syslinux.zytor.com/
+
+	N.B: Previously it was possible to write a kernel directly to
+	     a floppy using dd, configure the boot device using rdev, and
+	     boot using the resulting floppy. Linux no longer supports this
+	     method of booting.
+
+3.2) Booting from a cdrom using isolinux
+
+     	When building kernels, an easy way to create a bootable cdrom that
+     	uses isolinux is to use the isoimage target which uses a bzimage
+     	image. Like zdisk and bzdisk, this target accepts the FDARGS
+     	parameter which can be used to set the kernel command line.
+
+	e.g.
+	  make isoimage FDARGS="root=/dev/nfs"
+
+     	The resulting iso image will be arch/<ARCH>/boot/image.iso
+     	This can be written to a cdrom using a variety of tools including
+     	cdrecord.
+
+	e.g.
+	  cdrecord dev=ATAPI:1,0,0 arch/x86/boot/image.iso
+
+     	For more information on isolinux, including how to create bootdisks
+     	for prebuilt kernels, see http://syslinux.zytor.com/
+
+3.2) Using LILO
+	When using LILO all the necessary command line parameters may be
+	specified using the 'append=' directive in the LILO configuration
+	file.
+
+	However, to use the 'root=' directive you also need to create
+	a dummy root device, which may be removed after LILO is run.
+
+	mknod /dev/boot255 c 0 255
+
+	For information on configuring LILO, please refer to its documentation.
+
+3.3) Using GRUB
+	When using GRUB, kernel parameter are simply appended after the kernel
+	specification: kernel <kernel> <parameters>
+
+3.4) Using loadlin
+	loadlin may be used to boot Linux from a DOS command prompt without
+	requiring a local hard disk to mount as root. This has not been
+	thoroughly tested by the authors of this document, but in general
+	it should be possible configure the kernel command line similarly
+	to the configuration of LILO.
+
+	Please refer to the loadlin documentation for further information.
+
+3.5) Using a boot ROM
+	This is probably the most elegant way of booting a diskless client.
+	With a boot ROM the kernel is loaded using the TFTP protocol. The
+	authors of this document are not aware of any no commercial boot
+	ROMs that support booting Linux over the network. However, there
+	are two free implementations of a boot ROM, netboot-nfs and
+	etherboot, both of which are available on sunsite.unc.edu, and both
+	of which contain everything you need to boot a diskless Linux client.
+
+3.6) Using pxelinux
+	Pxelinux may be used to boot linux using the PXE boot loader
+	which is present on many modern network cards.
+
+	When using pxelinux, the kernel image is specified using
+	"kernel <relative-path-below /tftpboot>". The nfsroot parameters
+	are passed to the kernel by adding them to the "append" line.
+	It is common to use serial console in conjunction with pxeliunx,
+	see Documentation/admin-guide/serial-console.rst for more information.
+
+	For more information on isolinux, including how to create bootdisks
+	for prebuilt kernels, see http://syslinux.zytor.com/
+
+
+
+
+4.) Credits
+    -------
+
+  The nfsroot code in the kernel and the RARP support have been written
+  by Gero Kuhlmann <gero@gkminix.han.de>.
+
+  The rest of the IP layer autoconfiguration code has been written
+  by Martin Mares <mj@atrey.karlin.mff.cuni.cz>.
+
+  In order to write the initial version of nfsroot I would like to thank
+  Jens-Uwe Mager <jum@anubis.han.de> for his help.
diff --git a/Documentation/filesystems/nfs/pnfs-block-server.txt b/Documentation/filesystems/nfs/pnfs-block-server.txt
new file mode 100644
index 0000000..2143673
--- /dev/null
+++ b/Documentation/filesystems/nfs/pnfs-block-server.txt
@@ -0,0 +1,37 @@
+pNFS block layout server user guide
+
+The Linux NFS server now supports the pNFS block layout extension.  In this
+case the NFS server acts as Metadata Server (MDS) for pNFS, which in addition
+to handling all the metadata access to the NFS export also hands out layouts
+to the clients to directly access the underlying block devices that are
+shared with the client.
+
+To use pNFS block layouts with with the Linux NFS server the exported file
+system needs to support the pNFS block layouts (currently just XFS), and the
+file system must sit on shared storage (typically iSCSI) that is accessible
+to the clients in addition to the MDS.  As of now the file system needs to
+sit directly on the exported volume, striping or concatenation of
+volumes on the MDS and clients is not supported yet.
+
+On the server, pNFS block volume support is automatically if the file system
+support it.  On the client make sure the kernel has the CONFIG_PNFS_BLOCK
+option enabled, the blkmapd daemon from nfs-utils is running, and the
+file system is mounted using the NFSv4.1 protocol version (mount -o vers=4.1).
+
+If the nfsd server needs to fence a non-responding client it calls
+/sbin/nfsd-recall-failed with the first argument set to the IP address of
+the client, and the second argument set to the device node without the /dev
+prefix for the file system to be fenced. Below is an example file that shows
+how to translate the device into a serial number from SCSI EVPD 0x80:
+
+cat > /sbin/nfsd-recall-failed << EOF
+#!/bin/sh
+
+CLIENT="$1"
+DEV="/dev/$2"
+EVPD=`sg_inq --page=0x80 ${DEV} | \
+	grep "Unit serial number:" | \
+	awk -F ': ' '{print $2}'`
+
+echo "fencing client ${CLIENT} serial ${EVPD}" >> /var/log/pnfsd-fence.log
+EOF
diff --git a/Documentation/filesystems/nfs/pnfs-scsi-server.txt b/Documentation/filesystems/nfs/pnfs-scsi-server.txt
new file mode 100644
index 0000000..5bef726
--- /dev/null
+++ b/Documentation/filesystems/nfs/pnfs-scsi-server.txt
@@ -0,0 +1,23 @@
+
+pNFS SCSI layout server user guide
+==================================
+
+This document describes support for pNFS SCSI layouts in the Linux NFS server.
+With pNFS SCSI layouts, the NFS server acts as Metadata Server (MDS) for pNFS,
+which in addition to handling all the metadata access to the NFS export,
+also hands out layouts to the clients so that they can directly access the
+underlying SCSI LUNs that are shared with the client.
+
+To use pNFS SCSI layouts with with the Linux NFS server, the exported file
+system needs to support the pNFS SCSI layouts (currently just XFS), and the
+file system must sit on a SCSI LUN that is accessible to the clients in
+addition to the MDS.  As of now the file system needs to sit directly on the
+exported LUN, striping or concatenation of LUNs on the MDS and clients
+is not supported yet.
+
+On a server built with CONFIG_NFSD_SCSI, the pNFS SCSI volume support is
+automatically enabled if the file system is exported using the "pnfs"
+option and the underlying SCSI device support persistent reservations.
+On the client make sure the kernel has the CONFIG_PNFS_BLOCK option
+enabled, and the file system is mounted using the NFSv4.1 protocol
+version (mount -o vers=4.1).
diff --git a/Documentation/filesystems/nfs/pnfs.txt b/Documentation/filesystems/nfs/pnfs.txt
new file mode 100644
index 0000000..80dc0bd
--- /dev/null
+++ b/Documentation/filesystems/nfs/pnfs.txt
@@ -0,0 +1,73 @@
+Reference counting in pnfs:
+==========================
+
+The are several inter-related caches.  We have layouts which can
+reference multiple devices, each of which can reference multiple data servers.
+Each data server can be referenced by multiple devices.  Each device
+can be referenced by multiple layouts.  To keep all of this straight,
+we need to reference count.
+
+
+struct pnfs_layout_hdr
+----------------------
+The on-the-wire command LAYOUTGET corresponds to struct
+pnfs_layout_segment, usually referred to by the variable name lseg.
+Each nfs_inode may hold a pointer to a cache of these layout
+segments in nfsi->layout, of type struct pnfs_layout_hdr.
+
+We reference the header for the inode pointing to it, across each
+outstanding RPC call that references it (LAYOUTGET, LAYOUTRETURN,
+LAYOUTCOMMIT), and for each lseg held within.
+
+Each header is also (when non-empty) put on a list associated with
+struct nfs_client (cl_layouts).  Being put on this list does not bump
+the reference count, as the layout is kept around by the lseg that
+keeps it in the list.
+
+deviceid_cache
+--------------
+lsegs reference device ids, which are resolved per nfs_client and
+layout driver type.  The device ids are held in a RCU cache (struct
+nfs4_deviceid_cache).  The cache itself is referenced across each
+mount.  The entries (struct nfs4_deviceid) themselves are held across
+the lifetime of each lseg referencing them.
+
+RCU is used because the deviceid is basically a write once, read many
+data structure.  The hlist size of 32 buckets needs better
+justification, but seems reasonable given that we can have multiple
+deviceid's per filesystem, and multiple filesystems per nfs_client.
+
+The hash code is copied from the nfsd code base.  A discussion of
+hashing and variations of this algorithm can be found at:
+http://groups.google.com/group/comp.lang.c/browse_thread/thread/9522965e2b8d3809
+
+data server cache
+-----------------
+file driver devices refer to data servers, which are kept in a module
+level cache.  Its reference is held over the lifetime of the deviceid
+pointing to it.
+
+lseg
+----
+lseg maintains an extra reference corresponding to the NFS_LSEG_VALID
+bit which holds it in the pnfs_layout_hdr's list.  When the final lseg
+is removed from the pnfs_layout_hdr's list, the NFS_LAYOUT_DESTROYED
+bit is set, preventing any new lsegs from being added.
+
+layout drivers
+--------------
+
+PNFS utilizes what is called layout drivers. The STD defines 4 basic
+layout types: "files", "objects", "blocks", and "flexfiles". For each
+of these types there is a layout-driver with a common function-vectors
+table which are called by the nfs-client pnfs-core to implement the
+different layout types.
+
+Files-layout-driver code is in: fs/nfs/filelayout/.. directory
+Blocks-layout-driver code is in: fs/nfs/blocklayout/.. directory
+Flexfiles-layout-driver code is in: fs/nfs/flexfilelayout/.. directory
+
+blocks-layout setup
+-------------------
+
+TODO: Document the setup needs of the blocks layout driver
diff --git a/Documentation/filesystems/nfs/rpc-cache.txt b/Documentation/filesystems/nfs/rpc-cache.txt
new file mode 100644
index 0000000..ebcaaee
--- /dev/null
+++ b/Documentation/filesystems/nfs/rpc-cache.txt
@@ -0,0 +1,202 @@
+	This document gives a brief introduction to the caching
+mechanisms in the sunrpc layer that is used, in particular,
+for NFS authentication.
+
+CACHES
+======
+The caching replaces the old exports table and allows for
+a wide variety of values to be caches.
+
+There are a number of caches that are similar in structure though
+quite possibly very different in content and use.  There is a corpus
+of common code for managing these caches.
+
+Examples of caches that are likely to be needed are:
+  - mapping from IP address to client name
+  - mapping from client name and filesystem to export options
+  - mapping from UID to list of GIDs, to work around NFS's limitation
+    of 16 gids.
+  - mappings between local UID/GID and remote UID/GID for sites that
+    do not have uniform uid assignment
+  - mapping from network identify to public key for crypto authentication.
+
+The common code handles such things as:
+   - general cache lookup with correct locking
+   - supporting 'NEGATIVE' as well as positive entries
+   - allowing an EXPIRED time on cache items, and removing
+     items after they expire, and are no longer in-use.
+   - making requests to user-space to fill in cache entries
+   - allowing user-space to directly set entries in the cache
+   - delaying RPC requests that depend on as-yet incomplete
+     cache entries, and replaying those requests when the cache entry
+     is complete.
+   - clean out old entries as they expire.
+
+Creating a Cache
+----------------
+
+1/ A cache needs a datum to store.  This is in the form of a
+   structure definition that must contain a
+     struct cache_head
+   as an element, usually the first.
+   It will also contain a key and some content.
+   Each cache element is reference counted and contains
+   expiry and update times for use in cache management.
+2/ A cache needs a "cache_detail" structure that
+   describes the cache.  This stores the hash table, some
+   parameters for cache management, and some operations detailing how
+   to work with particular cache items.
+   The operations requires are:
+   	struct cache_head *alloc(void)
+		This simply allocates appropriate memory and returns
+   		a pointer to the cache_detail embedded within the
+		structure
+	void cache_put(struct kref *)
+		This is called when the last reference to an item is
+		dropped.  The pointer passed is to the 'ref' field
+		in the cache_head.  cache_put should release any
+		references create by 'cache_init' and, if CACHE_VALID
+		is set, any references created by cache_update.
+		It should then release the memory allocated by
+   		'alloc'.
+        int match(struct cache_head *orig, struct cache_head *new)
+		test if the keys in the two structures match.  Return
+		1 if they do, 0 if they don't.
+	void init(struct cache_head *orig, struct cache_head *new)
+		Set the 'key' fields in 'new' from 'orig'.  This may
+		include taking references to shared objects.
+	void update(struct cache_head *orig, struct cache_head *new)
+		Set the 'content' fileds in 'new' from 'orig'.
+	int cache_show(struct seq_file *m, struct cache_detail *cd,
+			struct cache_head *h)
+		Optional.  Used to provide a /proc file that lists the
+		contents of a cache.  This should show one item,
+   		usually on just one line.
+	int cache_request(struct cache_detail *cd, struct cache_head *h,
+   		char **bpp, int *blen)
+		Format a request to be send to user-space for an item
+   		to be instantiated.  *bpp is a buffer of size *blen.
+		bpp should be moved forward over the encoded message,
+		and  *blen should be reduced to show how much free
+		space remains.  Return 0 on success or <0 if not
+		enough room or other problem.
+	int cache_parse(struct cache_detail *cd, char *buf, int len)
+		A message from user space has arrived to fill out a
+		cache entry.  It is in 'buf' of length 'len'.
+		cache_parse should parse this, find the item in the
+		cache with sunrpc_cache_lookup, and update the item
+		with sunrpc_cache_update.
+
+
+3/ A cache needs to be registered using cache_register().  This
+   includes it on a list of caches that will be regularly
+   cleaned to discard old data.
+
+Using a cache
+-------------
+
+To find a value in a cache, call sunrpc_cache_lookup passing a pointer
+to the cache_head in a sample item with the 'key' fields filled in.
+This will be passed to ->match to identify the target entry.  If no
+entry is found, a new entry will be create, added to the cache, and
+marked as not containing valid data.
+
+The item returned is typically passed to cache_check which will check
+if the data is valid, and may initiate an up-call to get fresh data.
+cache_check will return -ENOENT in the entry is negative or if an up
+call is needed but not possible, -EAGAIN if an upcall is pending,
+or 0 if the data is valid;
+
+cache_check can be passed a "struct cache_req *".  This structure is
+typically embedded in the actual request and can be used to create a
+deferred copy of the request (struct cache_deferred_req).  This is
+done when the found cache item is not uptodate, but the is reason to
+believe that userspace might provide information soon.  When the cache
+item does become valid, the deferred copy of the request will be
+revisited (->revisit).  It is expected that this method will
+reschedule the request for processing.
+
+The value returned by sunrpc_cache_lookup can also be passed to
+sunrpc_cache_update to set the content for the item.  A second item is
+passed which should hold the content.  If the item found by _lookup
+has valid data, then it is discarded and a new item is created.  This
+saves any user of an item from worrying about content changing while
+it is being inspected.  If the item found by _lookup does not contain
+valid data, then the content is copied across and CACHE_VALID is set.
+
+Populating a cache
+------------------
+
+Each cache has a name, and when the cache is registered, a directory
+with that name is created in /proc/net/rpc
+
+This directory contains a file called 'channel' which is a channel
+for communicating between kernel and user for populating the cache.
+This directory may later contain other files of interacting
+with the cache.
+
+The 'channel' works a bit like a datagram socket. Each 'write' is
+passed as a whole to the cache for parsing and interpretation.
+Each cache can treat the write requests differently, but it is
+expected that a message written will contain:
+  - a key
+  - an expiry time
+  - a content.
+with the intention that an item in the cache with the give key
+should be create or updated to have the given content, and the
+expiry time should be set on that item.
+
+Reading from a channel is a bit more interesting.  When a cache
+lookup fails, or when it succeeds but finds an entry that may soon
+expire, a request is lodged for that cache item to be updated by
+user-space.  These requests appear in the channel file.
+
+Successive reads will return successive requests.
+If there are no more requests to return, read will return EOF, but a
+select or poll for read will block waiting for another request to be
+added.
+
+Thus a user-space helper is likely to:
+  open the channel.
+    select for readable
+    read a request
+    write a response
+  loop.
+
+If it dies and needs to be restarted, any requests that have not been
+answered will still appear in the file and will be read by the new
+instance of the helper.
+
+Each cache should define a "cache_parse" method which takes a message
+written from user-space and processes it.  It should return an error
+(which propagates back to the write syscall) or 0.
+
+Each cache should also define a "cache_request" method which
+takes a cache item and encodes a request into the buffer
+provided.
+
+Note: If a cache has no active readers on the channel, and has had not
+active readers for more than 60 seconds, further requests will not be
+added to the channel but instead all lookups that do not find a valid
+entry will fail.  This is partly for backward compatibility: The
+previous nfs exports table was deemed to be authoritative and a
+failed lookup meant a definite 'no'.
+
+request/response format
+-----------------------
+
+While each cache is free to use its own format for requests
+and responses over channel, the following is recommended as
+appropriate and support routines are available to help:
+Each request or response record should be printable ASCII
+with precisely one newline character which should be at the end.
+Fields within the record should be separated by spaces, normally one.
+If spaces, newlines, or nul characters are needed in a field they
+much be quoted.  two mechanisms are available:
+1/ If a field begins '\x' then it must contain an even number of
+   hex digits, and pairs of these digits provide the bytes in the
+   field.
+2/ otherwise a \ in the field must be followed by 3 octal digits
+   which give the code for a byte.  Other characters are treated
+   as them selves.  At the very least, space, newline, nul, and
+   '\' must be quoted in this way.
diff --git a/Documentation/filesystems/nfs/rpc-server-gss.txt b/Documentation/filesystems/nfs/rpc-server-gss.txt
new file mode 100644
index 0000000..310bbba
--- /dev/null
+++ b/Documentation/filesystems/nfs/rpc-server-gss.txt
@@ -0,0 +1,91 @@
+
+rpcsec_gss support for kernel RPC servers
+=========================================
+
+This document gives references to the standards and protocols used to
+implement RPCGSS authentication in kernel RPC servers such as the NFS
+server and the NFS client's NFSv4.0 callback server.  (But note that
+NFSv4.1 and higher don't require the client to act as a server for the
+purposes of authentication.)
+
+RPCGSS is specified in a few IETF documents:
+ - RFC2203 v1: http://tools.ietf.org/rfc/rfc2203.txt
+ - RFC5403 v2: http://tools.ietf.org/rfc/rfc5403.txt
+and there is a 3rd version  being proposed:
+ - http://tools.ietf.org/id/draft-williams-rpcsecgssv3.txt
+   (At draft n. 02 at the time of writing)
+
+Background
+----------
+
+The RPCGSS Authentication method describes a way to perform GSSAPI
+Authentication for NFS.  Although GSSAPI is itself completely mechanism
+agnostic, in many cases only the KRB5 mechanism is supported by NFS
+implementations.
+
+The Linux kernel, at the moment, supports only the KRB5 mechanism, and
+depends on GSSAPI extensions that are KRB5 specific.
+
+GSSAPI is a complex library, and implementing it completely in kernel is
+unwarranted. However GSSAPI operations are fundementally separable in 2
+parts:
+- initial context establishment
+- integrity/privacy protection (signing and encrypting of individual
+  packets)
+
+The former is more complex and policy-independent, but less
+performance-sensitive.  The latter is simpler and needs to be very fast.
+
+Therefore, we perform per-packet integrity and privacy protection in the
+kernel, but leave the initial context establishment to userspace.  We
+need upcalls to request userspace to perform context establishment.
+
+NFS Server Legacy Upcall Mechanism
+----------------------------------
+
+The classic upcall mechanism uses a custom text based upcall mechanism
+to talk to a custom daemon called rpc.svcgssd that is provide by the
+nfs-utils package.
+
+This upcall mechanism has 2 limitations:
+
+A) It can handle tokens that are no bigger than 2KiB
+
+In some Kerberos deployment GSSAPI tokens can be quite big, up and
+beyond 64KiB in size due to various authorization extensions attacked to
+the Kerberos tickets, that needs to be sent through the GSS layer in
+order to perform context establishment.
+
+B) It does not properly handle creds where the user is member of more
+than a few thousand groups (the current hard limit in the kernel is 65K
+groups) due to limitation on the size of the buffer that can be send
+back to the kernel (4KiB).
+
+NFS Server New RPC Upcall Mechanism
+-----------------------------------
+
+The newer upcall mechanism uses RPC over a unix socket to a daemon
+called gss-proxy, implemented by a userspace program called Gssproxy.
+
+The gss_proxy RPC protocol is currently documented here:
+
+	https://fedorahosted.org/gss-proxy/wiki/ProtocolDocumentation
+
+This upcall mechanism uses the kernel rpc client and connects to the gssproxy
+userspace program over a regular unix socket. The gssproxy protocol does not
+suffer from the size limitations of the legacy protocol.
+
+Negotiating Upcall Mechanisms
+-----------------------------
+
+To provide backward compatibility, the kernel defaults to using the
+legacy mechanism.  To switch to the new mechanism, gss-proxy must bind
+to /var/run/gssproxy.sock and then write "1" to
+/proc/net/rpc/use-gss-proxy.  If gss-proxy dies, it must repeat both
+steps.
+
+Once the upcall mechanism is chosen, it cannot be changed.  To prevent
+locking into the legacy mechanisms, the above steps must be performed
+before starting nfsd.  Whoever starts nfsd can guarantee this by reading
+from /proc/net/rpc/use-gss-proxy and checking that it contains a
+"1"--the read will block until gss-proxy has done its write to the file.