nfs: new subdir Documentation/filesystems/nfs

We're adding enough nfs documentation that it may as well have its own
subdirectory.

Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

6 files changed, 1020 insertions, 0 deletions

diff --git a/Documentation/filesystems/nfs/00-INDEX b/Documentation/filesystems/nfs/00-INDEX
new file mode 100644
index 000000000000..6ff3d212027b
--- /dev/null
+++ b/Documentation/filesystems/nfs/00-INDEX
@@ -0,0 +1,12 @@
+00-INDEX
+        - this file (nfs-related documentation).
+Exporting
+        - explanation of how to make filesystems exportable.
+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
+nfsroot.txt
+        - short guide on setting up a diskless box with NFS root filesystem.
diff --git a/Documentation/filesystems/nfs/Exporting b/Documentation/filesystems/nfs/Exporting
new file mode 100644
index 000000000000..87019d2b5981
--- /dev/null
+++ b/Documentation/filesystems/nfs/Exporting
@@ -0,0 +1,147 @@
+
+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. 
+
+b/ A per-superblock list "s_anon" of dentries which are the roots of
+   subtrees that are not in the proper prefix.  These dentries, as
+   well as the proper prefix, need to be released at unmount time.  As
+   these dentries will not be hashed, they are linked together on the
+   d_hash list_head.
+
+c/ Helper routines to allocate anonymous dentries, and to help attach
+   loose directory dentries at lookup time. They are:
+    d_alloc_anon(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 make sure that there is a
+      dentry with the same name and parent as the given dentry, and
+      which refers to the given inode.
+      If the inode is a directory and already has a dentry, then that
+      dentry is d_moved over the given dentry.
+      If the passed dentry gets attached, care is taken that this is
+      mutually exclusive to a d_alloc_anon operation.
+      If the passed dentry is used, NULL is returned, else the used
+      dentry is returned.  This corresponds to the calling pattern 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.
+      Typically the ->lookup routine will 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_alloc_anon).
+
+  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_alloc_anon).
+    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/nfs-rdma.txt b/Documentation/filesystems/nfs/nfs-rdma.txt
new file mode 100644
index 000000000000..e386f7e4bcee
--- /dev/null
+++ b/Documentation/filesystems/nfs/nfs-rdma.txt
@@ -0,0 +1,271 @@
+################################################################################
+#                                                                              #
+#                               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 2.6 Linux
+    kernel can be found at:
+
+    ftp://ftp.kernel.org/pub/linux/kernel/v2.6/
+
+    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$ ifconfig ib0 a.b.c.x
+    host2$ ifconfig 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 cleint'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
+    $ ifconfig 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 000000000000..f50f26ce6cd0
--- /dev/null
+++ b/Documentation/filesystems/nfs/nfs.txt
@@ -0,0 +1,98 @@
+
+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
+upcall interfaces that are used in order to provide the NFS client with
+some of the information that it requires in order to fully comply with
+the NFS spec.
+
+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 000000000000..1bd0d0c05171
--- /dev/null
+++ b/Documentation/filesystems/nfs/nfs41-server.txt
@@ -0,0 +1,222 @@
+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 disabled by default.
+It can be enabled 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.  Use your user-mode
+nfs-utils to set this up; 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 the latest NFSv4.1 Internet Draft:
+http://tools.ietf.org/html/draft-ietf-nfsv4-minorversion1-29
+
+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.
+
+Other NFSv4.1 features, Parallel NFS operations in particular,
+are still under development out of tree.
+See http://wiki.linux-nfs.org/wiki/index.php/PNFS_prototype_design
+for more information.
+
+The current implementation is intended for developers only: while it
+does support ordinary file operations on clients we have tested against
+(including the linux client), it is incomplete in ways which may limit
+features unexpectedly, cause known bugs in rare cases, or cause
+interoperability problems with future clients.  Known issues:
+
+        - gss support is questionable: currently mounts with kerberos
+          from a linux client are possible, but we aren't really
+          conformant with the spec (for example, we don't use kerberos
+          on the backchannel correctly).
+        - no trunking support: no clients currently take advantage of
+          trunking, but this is a mandatory feature, and its use is
+          recommended to clients in a number of places.  (E.g. to ensure
+          timely renewal in case an existing connection's retry timeouts
+          have gotten too long; see section 8.3 of the draft.)
+          Therefore, lack of this feature may cause future clients to
+          fail.
+        - Incomplete backchannel support: incomplete backchannel gss
+          support and no support for BACKCHANNEL_CTL mean that
+          callbacks (hence delegations and layouts) may not be
+          available and clients confused by the incomplete
+          implementation may fail.
+        - Server reboot recovery is unsupported; if the server reboots,
+          clients may fail.
+        - We do not support SSV, which provides security for shared
+          client-server state (thus preventing unauthorized tampering
+          with locks and opens, for example).  It is mandatory for
+          servers to support this, though no clients use it yet.
+        - Mandatory operations which we do not support, such as
+          DESTROY_CLIENTID, FREE_STATEID, SECINFO_NO_NAME, and
+          TEST_STATEID, are not currently used by clients, but will be
+          (and the spec recommends their uses in common cases), and
+          clients should not be expected to know how to recover from the
+          case where they are not supported.  This will eventually cause
+          interoperability failures.
+
+In addition, some limitations are inherited from the current NFSv4
+implementation:
+
+        - Incomplete delegation enforcement: if a file is renamed or
+          unlinked, a client holding a delegation may continue to
+          indefinitely allow opens of the file under the old name.
+
+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.
+        P       pNFS features implemented out of tree.
+        PNS     pNFS features that are not supported yet (out of tree).
+
+Operations
+
+   +----------------------+------------+--------------+----------------+
+   | Operation            | REQ, REC,  | Feature      | Definition     |
+   |                      | OPT, or    | (REQ, REC,   |                |
+   |                      | MNI        | or OPT)      |                |
+   +----------------------+------------+--------------+----------------+
+   | ACCESS               | REQ        |              | Section 18.1   |
+NS | BACKCHANNEL_CTL      | REQ        |              | Section 18.33  |
+NS | 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)        |                |
+NS | DESTROY_CLIENTID     | REQ        |              | Section 18.50  |
+I  | DESTROY_SESSION      | REQ        |              | Section 18.37  |
+I  | EXCHANGE_ID          | REQ        |              | Section 18.35  |
+NS | FREE_STATEID         | REQ        |              | Section 18.38  |
+   | GETATTR              | REQ        |              | Section 18.7   |
+P  | GETDEVICEINFO        | OPT        | pNFS (REQ)   | Section 18.40  |
+P  | GETDEVICELIST        | OPT        | pNFS (OPT)   | Section 18.41  |
+   | GETFH                | REQ        |              | Section 18.8   |
+NS*| GET_DIR_DELEGATION   | OPT        | DDELG (REQ)  | Section 18.39  |
+P  | LAYOUTCOMMIT         | OPT        | pNFS (REQ)   | Section 18.42  |
+P  | LAYOUTGET            | OPT        | pNFS (REQ)   | Section 18.43  |
+P  | 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  |
+NS | 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  |
+NS | 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  |
+NS | 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  |
+P  | CB_LAYOUTRECALL         | OPT       | pNFS (REQ)  | Section 20.3  |
+NS*| CB_NOTIFY               | OPT       | DDELG (REQ) | Section 20.4  |
+P  | 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:
+
+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:
+* only SP4_NONE state protection supported
+* implementation ids are ignored
+
+CREATE_SESSION:
+* backchannel attributes are ignored
+* backchannel security parameters are ignored
+
+SEQUENCE:
+* no support for dynamic slot table renegotiation (optional)
+
+nfsv4.1 COMPOUND rules:
+The following cases aren't supported yet:
+* Enforcing of NFS4ERR_NOT_ONLY_OP for: BIND_CONN_TO_SESSION, CREATE_SESSION,
+  DESTROY_CLIENTID, DESTROY_SESSION, EXCHANGE_ID.
+* DESTROY_SESSION MUST be the final operation in the COMPOUND request.
+
+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.
+* No more than one IO operation (read, write, readdir) allowed per
+  compound.
diff --git a/Documentation/filesystems/nfs/nfsroot.txt b/Documentation/filesystems/nfs/nfsroot.txt
new file mode 100644
index 000000000000..3ba0b945aaf8
--- /dev/null
+++ b/Documentation/filesystems/nfs/nfsroot.txt
@@ -0,0 +1,270 @@
+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>
+
+
+
+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/initrd.txt) 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>
+
+  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.
+
+                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. May be supplied by autoconfiguration,
+                but its absence will not trigger autoconfiguration.
+
+                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)
+
+                Default: any
+
+
+
+
+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/i386/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/serial-console.txt 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.