nfs/hostname
For Kerberos V5, nfs/hostname would be a server principal in the
Kerberos Key Distribution Center database. For LIPKEY, this would be
the username passed to the target (the NFS version 4 client that
receives the callback).
It should be noted that LIPKEY may not work for callbacks, since the
LIPKEY client uses a user id/password. If the NFS client receiving
the callback can authenticate the NFS server's user name/password
pair, and if the user that the NFS server is authenticating to has a
public key certificate, then it works.
In situations where NFS client uses LIPKEY and uses a per-host
principal for the SETCLIENTID operation, instead of using LIPKEY for
SETCLIENTID, it is RECOMMENDED that SPKM-3 with mutual authentication
be used. This effectively means that the client will use a
certificate to authenticate and identify the initiator to the target
on the NFS server. Using SPKM-3 and not LIPKEY has the following
advantages:
o When the server does a callback, it must authenticate to the
principal used in the SETCLIENTID. Even if LIPKEY is used,
because LIPKEY is layered over SPKM-3, the NFS client will need to
have a certificate that corresponds to the principal used in the
SETCLIENTID operation. From an administrative perspective, having
a user name, password, and certificate for both the client and
server is redundant.
o LIPKEY was intended to minimize additional infrastructure
requirements beyond a certificate for the target, and the
expectation is that existing password infrastructure can be
leveraged for the initiator. In some environments, a per-host
password does not exist yet. If certificates are used for any
per-host principals, then additional password infrastructure is
not needed.
o In cases when a host is both an NFS client and server, it can
share the same per-host certificate.
4. Filehandles
The filehandle in the NFS protocol is a per server unique identifier
for a file system object. The contents of the filehandle are opaque
to the client. Therefore, the server is responsible for translating
the filehandle to an internal representation of the file system
object. Since the filehandle is the client's reference to an object
and the client may cache this reference, the server SHOULD not reuse
a filehandle for another file system object. If the server needs to
reuse a filehandle value, the time elapsed before reuse SHOULD be
large enough such that it is unlikely the client has a cached copy of
the reused filehandle value. Note that a client may cache a
filehandle for a very long time. For example, a client may cache NFS
data to local storage as a method to expand its effective cache size
and as a means to survive client restarts. Therefore, the lifetime
of a cached filehandle may be extended.
4.1. Obtaining the First Filehandle
The operations of the NFS protocol are defined in terms of one or
more filehandles. Therefore, the client needs a filehandle to
initiate communication with the server. With the NFS version 2
protocol [RFC1094] and the NFS version 3 protocol [RFC1813], there
exists an ancillary protocol to obtain this first filehandle. The
MOUNT protocol, RPC program number 100005, provides the mechanism of
translating a string based file system path name to a filehandle
which can then be used by the NFS protocols.
The MOUNT protocol has deficiencies in the area of security and use
via firewalls. This is one reason that the use of the public
filehandle was introduced in [RFC2054] and [RFC2055]. With the use
of the public filehandle in combination with the LOOKUP procedure in
the NFS version 2 and 3 protocols, it has been demonstrated that the
MOUNT protocol is unnecessary for viable interaction between NFS
client and server.
Therefore, the NFS version 4 protocol will not use an ancillary
protocol for translation from string based path names to a
filehandle. Two special filehandles will be used as starting points
for the NFS client.
4.1.1. Root Filehandle
The first of the special filehandles is the ROOT filehandle. The
ROOT filehandle is the "conceptual" root of the file system name
space at the NFS server. The client uses or starts with the ROOT
filehandle by employing the PUTROOTFH operation. The PUTROOTFH
operation instructs the server to set the "current" filehandle to the
ROOT of the server's file tree. Once this PUTROOTFH operation is
used, the client can then traverse the entirety of the server's file
tree with the LOOKUP procedure. A complete discussion of the server
name space is in the section "NFS Server Name Space".
4.1.2. Public Filehandle
The second special filehandle is the PUBLIC filehandle. Unlike the
ROOT filehandle, the PUBLIC filehandle may be bound or represent an
arbitrary file system object at the server. The server is
responsible for this binding. It may be that the PUBLIC filehandle
and the ROOT filehandle refer to the same file system object.
However, it is up to the administrative software at the server and
the policies of the server administrator to define the binding of the
PUBLIC filehandle and server file system object. The client may not
make any assumptions about this binding.
4.2. Filehandle Types
In the NFS version 2 and 3 protocols, there was one type of
filehandle with a single set of semantics. The NFS version 4
protocol introduces a new type of filehandle in an attempt to
accommodate certain server environments. The first type of
filehandle is 'persistent'. The semantics of a persistent filehandle
are the same as the filehandles of the NFS version 2 and 3 protocols.
The second or new type of filehandle is the "volatile" filehandle.
The volatile filehandle type is being introduced to address server
functionality or implementation issues which make correct
implementation of a persistent filehandle infeasible. Some server
environments do not provide a file system level invariant that can be
used to construct a persistent filehandle. The underlying server
file system may not provide the invariant or the server's file system
programming interfaces may not provide access to the needed
invariant. Volatile filehandles may ease the implementation of
server functionality such as hierarchical storage management or file
system reorganization or migration. However, the volatile filehandle
increases the implementation burden for the client. However this
increased burden is deemed acceptable based on the overall gains
achieved by the protocol.
Since the client will need to handle persistent and volatile
filehandle differently, a file attribute is defined which may be used
by the client to determine the filehandle types being returned by the
server.
4.2.1. General Properties of a Filehandle
The filehandle contains all the information the server needs to
distinguish an individual file. To the client, the filehandle is
opaque. The client stores filehandles for use in a later request and
can compare two filehandles from the same server for equality by
doing a byte-by-byte comparison. However, the client MUST NOT
otherwise interpret the contents of filehandles. If two filehandles
from the same server are equal, they MUST refer to the same file. If
they are not equal, the client may use information provided by the
server, in the form of file attributes, to determine whether they
denote the same files or different files. The client would do this
as necessary for client side caching. Servers SHOULD try to maintain
a one-to-one correspondence between filehandles and files but this is
not required. Clients MUST use filehandle comparisons only to
improve performance, not for correct behavior. All clients need to
be prepared for situations in which it cannot be determined whether
two filehandles denote the same object and in such cases, avoid
making invalid assumptions which might cause incorrect behavior.
Further discussion of filehandle and attribute comparison in the
context of data caching is presented in the section "Data Caching and
File Identity".
As an example, in the case that two different path names when
traversed at the server terminate at the same file system object, the
server SHOULD return the same filehandle for each path. This can
occur if a hard link is used to create two file names which refer to
the same underlying file object and associated data. For example, if
paths /a/b/c and /a/d/c refer to the same file, the server SHOULD
return the same filehandle for both path names traversals.
4.2.2. Persistent Filehandle
A persistent filehandle is defined as having a fixed value for the
lifetime of the file system object to which it refers. Once the
server creates the filehandle for a file system object, the server
MUST accept the same filehandle for the object for the lifetime of
the object. If the server restarts or reboots the NFS server must
honor the same filehandle value as it did in the server's previous
instantiation. Similarly, if the file system is migrated, the new
NFS server must honor the same file handle as the old NFS server.
The persistent filehandle will be become stale or invalid when the
file system object is removed. When the server is presented with a
persistent filehandle that refers to a deleted object, it MUST return
an error of NFS4ERR_STALE. A filehandle may become stale when the
file system containing the object is no longer available. The file
system may become unavailable if it exists on removable media and the
media is no longer available at the server or the file system in
whole has been destroyed or the file system has simply been removed
from the server's name space (i.e. unmounted in a Unix environment).
4.2.3. Volatile Filehandle
A volatile filehandle does not share the same longevity
characteristics of a persistent filehandle. The server may determine
that a volatile filehandle is no longer valid at many different
points in time. If the server can definitively determine that a
volatile filehandle refers to an object that has been removed, the
server should return NFS4ERR_STALE to the client (as is the case for
persistent filehandles). In all other cases where the server
determines that a volatile filehandle can no longer be used, it
should return an error of NFS4ERR_FHEXPIRED.
The mandatory attribute "fh_expire_type" is used by the client to
determine what type of filehandle the server is providing for a
particular file system. This attribute is a bitmask with the
following values:
FH4_PERSISTENT
The value of FH4_PERSISTENT is used to indicate a persistent
filehandle, which is valid until the object is removed from the
file system. The server will not return NFS4ERR_FHEXPIRED for
this filehandle. FH4_PERSISTENT is defined as a value in which
none of the bits specified below are set.
FH4_NOEXPIRE_WITH_OPEN
The filehandle will not expire while client has the file open.
If this bit is set, then the values FH4_VOLATILE_ANY or
FH4_VOL_RENAME do not impact expiration while the file is open.
Once the file is closed or if the FH4_NOEXPIRE_WITH_OPEN bit is
false, the rest of the volatile related bits apply.
FH4_VOLATILE_ANY
The filehandle may expire at any time and will expire during
system migration and rename.
FH4_VOL_MIGRATION
The filehandle will expire during file system migration. May
only be set if FH4_VOLATILE_ANY is not set.
FH4_VOL_RENAME
The filehandle may expire due to a rename. This includes a
rename by the requesting client or a rename by another client.
May only be set if FH4_VOLATILE_ANY is not set.
Servers which provide volatile filehandles should deny a RENAME or
REMOVE that would affect an OPEN file or any of the components
leading to the OPEN file. In addition, the server should deny all
RENAME or REMOVE requests during the grace or lease period upon
server restart.
The reader may be wondering why there are three FH4_VOL* bits and why
FH4_VOLATILE_ANY is exclusive of FH4_VOL_MIGRATION and
FH4_VOL_RENAME. If the a filehandle is normally persistent but
cannot persist across a file set migration, then the presence of the
FH4_VOL_MIGRATION or FH4_VOL_RENAME tells the client that it can
treat the file handle as persistent for purposes of maintaining a
file name to file handle cache, except for the specific event
described by the bit. However, FH4_VOLATILE_ANY tells the client
that it should not maintain such a cache for unopened files. A
server MUST not present FH4_VOLATILE_ANY with FH4_VOL_MIGRATION or
FH4_VOL_RENAME as this will lead to confusion. FH4_VOLATILE_ANY
implies that the file handle will expire upon migration or rename, in
addition to other events.
4.2.4. One Method of Constructing a Volatile Filehandle
As mentioned, in some instances a filehandle is stale (no longer
valid; perhaps because the file was removed from the server) or it is
expired (the underlying file is valid but since the filehandle is
volatile, it may have expired). Thus the server needs to be able to
return NFS4ERR_STALE in the former case and NFS4ERR_FHEXPIRED in the
latter case. This can be done by careful construction of the volatile
filehandle. One possible implementation follows.
A volatile filehandle, while opaque to the client could contain:
[volatile bit = 1 | server boot time | slot | generation number]
o slot is an index in the server volatile filehandle table
o generation number is the generation number for the table
entry/slot
If the server boot time is less than the current server boot time,
return NFS4ERR_FHEXPIRED. If slot is out of range, return
NFS4ERR_BADHANDLE. If the generation number does not match, return
NFS4ERR_FHEXPIRED.
When the server reboots, the table is gone (it is volatile).
If volatile bit is 0, then it is a persistent filehandle with a
different structure following it.
4.3. Client Recovery from Filehandle Expiration
If possible, the client SHOULD recover from the receipt of an
NFS4ERR_FHEXPIRED error. The client must take on additional
responsibility so that it may prepare itself to recover from the
expiration of a volatile filehandle. If the server returns
persistent filehandles, the client does not need these additional
steps.
For volatile filehandles, most commonly the client will need to store
the component names leading up to and including the file system
object in question. With these names, the client should be able to
recover by finding a filehandle in the name space that is still
available or by starting at the root of the server's file system name
space.
If the expired filehandle refers to an object that has been removed
from the file system, obviously the client will not be able to
recover from the expired filehandle.
It is also possible that the expired filehandle refers to a file that
has been renamed. If the file was renamed by another client, again
it is possible that the original client will not be able to recover.
However, in the case that the client itself is renaming the file and
the file is open, it is possible that the client may be able to
recover. The client can determine the new path name based on the
processing of the rename request. The client can then regenerate the
new filehandle based on the new path name. The client could also use
the compound operation mechanism to construct a set of operations
like:
RENAME A B
LOOKUP B
GETFH
5. File Attributes
To meet the requirements of extensibility and increased
interoperability with non-Unix platforms, attributes must be handled
in a flexible manner. The NFS Version 3 fattr3 structure contains a
fixed list of attributes that not all clients and servers are able to
support or care about. The fattr3 structure can not be extended as
new needs arise and it provides no way to indicate non-support. With
the NFS Version 4 protocol, the client will be able to ask what
attributes the server supports and will be able to request only those
attributes in which it is interested.
To this end, attributes will be divided into three groups: mandatory,
recommended, and named. Both mandatory and recommended attributes
are supported in the NFS version 4 protocol by a specific and well-
defined encoding and are identified by number. They are requested by
setting a bit in the bit vector sent in the GETATTR request; the
server response includes a bit vector to list what attributes were
returned in the response. New mandatory or recommended attributes
may be added to the NFS protocol between major revisions by
publishing a standards-track RFCwhich allocates a new attribute
number value and defines the encoding for the attribute. See the
section "Minor Versioning" for further discussion.
Named attributes are accessed by the new OPENATTR operation, which
accesses a hidden directory of attributes associated with a file
system object. OPENATTR takes a filehandle for the object and
returns the filehandle for the attribute hierarchy. The filehandle
for the named attributes is a directory object accessible by LOOKUP
or READDIR and contains files whose names represent the named
attributes and whose data bytes are the value of the attribute. For
example:
LOOKUP "foo" ; look up file
GETATTR attrbits
OPENATTR ; access foo's named attributes
LOOKUP "x11icon" ; look up specific attribute
READ 0,4096 ; read stream of bytes
Named attributes are intended for data needed by applications rather
than by an NFS client implementation. NFS implementors are strongly
encouraged to define their new attributes as recommended attributes
by bringing them to the IETF standards-track process.
The set of attributes which are classified as mandatory is
deliberately small since servers must do whatever it takes to support
them. The recommended attributes may be unsupported; though a server
should support as many as it can. Attributes are deemed mandatory if
the data is both needed by a large number of clients and is not
otherwise reasonably computable by the client when support is not
provided on the server.
5.1. Mandatory Attributes
These MUST be supported by every NFS Version 4 client and server in
order to ensure a minimum level of interoperability. The server must
store and return these attributes and the client must be able to
function with an attribute set limited to these attributes. With
just the mandatory attributes some client functionality may be
impaired or limited in some ways. A client may ask for any of these
attributes to be returned by setting a bit in the GETATTR request and
the server must return their value.
5.2. Recommended Attributes
These attributes are understood well enough to warrant support in the
NFS Version 4 protocol. However, they may not be supported on all
clients and servers. A client may ask for any of these attributes to
be returned by setting a bit in the GETATTR request but must handle
the case where the server does not return them. A client may ask for
the set of attributes the server supports and should not request
attributes the server does not support. A server should be tolerant
of requests for unsupported attributes and simply not return them
rather than considering the request an error. It is expected that
servers will support all attributes they comfortably can and only
fail to support attributes which are difficult to support in their
operating environments. A server should provide attributes whenever
they don't have to "tell lies" to the client. For example, a file
modification time should be either an accurate time or should not be
supported by the server. This will not always be comfortable to
clients but it seems that the client has a better ability to
fabricate or construct an attribute or do without the attribute.
5.3. Named Attributes
These attributes are not supported by direct encoding in the NFS
Version 4 protocol but are accessed by string names rather than
numbers and correspond to an uninterpreted stream of bytes which are
stored with the file system object. The name space for these
attributes may be accessed by using the OPENATTR operation. The
OPENATTR operation returns a filehandle for a virtual "attribute
directory" and further perusal of the name space may be done using
READDIR and LOOKUP operations on this filehandle. Named attributes
may then be examined or changed by normal READ and WRITE and CREATE
operations on the filehandles returned from READDIR and LOOKUP.
Named attributes may have attributes.
It is recommended that servers support arbitrary named attributes. A
client should not depend on the ability to store any named attributes
in the server's file system. If a server does support named
attributes, a client which is also able to handle them should be able
to copy a file's data and meta-data with complete transparency from
one location to another; this would imply that names allowed for
regular directory entries are valid for named attribute names as
well.
Names of attributes will not be controlled by this document or other
IETF standards track documents. See the section "IANA
Considerations" for further discussion.
5.4. Mandatory Attributes - Definitions
Name # DataType Access Description
___________________________________________________________________
supp_attr 0 bitmap READ The bit vector which
would retrieve all
mandatory and
recommended attributes
that are supported for
this object.
type 1 nfs4_ftype READ The type of the object
(file, directory,
symlink)
fh_expire_type 2 uint32 READ Server uses this to
specify filehandle
expiration behavior to
the client. See the
section "Filehandles"
for additional
description.
change 3 uint64 READ A value created by the
server that the client
can use to determine
if file data,
directory contents or
attributes of the
object have been
modified. The server
may return the
object's time_modify
attribute for this
attribute's value but
only if the file
system object can not
be updated more
frequently than the
resolution of
time_modify.
size 4 uint64 R/W The size of the object
in bytes.
link_support 5 boolean READ Does the object's file
system supports hard
links?
symlink_support 6 boolean READ Does the object's file
system supports
symbolic links?
named_attr 7 boolean READ Does this object have
named attributes?
fsid 8 fsid4 READ Unique file system
identifier for the
file system holding
this object. fsid
contains major and
minor components each
of which are uint64.
unique_handles 9 boolean READ Are two distinct
filehandles guaranteed
to refer to two
different file system
objects?
lease_time 10 nfs_lease4 READ Duration of leases at
server in seconds.
rdattr_error 11 enum READ Error returned from
getattr during
readdir.
5.5. Recommended Attributes - Definitions
Name # Data Type Access Description
_____________________________________________________________________
ACL 12 nfsace4<> R/W The access control
list for the object.
aclsupport 13 uint32 READ Indicates what types
of ACLs are supported
on the current file
system.
archive 14 boolean R/W Whether or not this
file has been
archived since the
time of last
modification
(deprecated in favor
of time_backup).
cansettime 15 boolean READ Is the server able to
change the times for
a file system object
as specified in a
SETATTR operation?
case_insensitive 16 boolean READ Are filename
comparisons on this
file system case
insensitive?
case_preserving 17 boolean READ Is filename case on
this file system
preserved?
chown_restricted 18 boolean READ If TRUE, the server
will reject any
request to change
either the owner or
the group associated
with a file if the
caller is not a
privileged user (for
example, "root" in
Unix operating
environments or in NT
the "Take Ownership"
privilege)
filehandle 19 nfs4_fh READ The filehandle of
this object
(primarily for
readdir requests).
fileid 20 uint64 READ A number uniquely
identifying the file
within the file
system.
files_avail 21 uint64 READ File slots available
to this user on the
file system
containing this
object - this should
be the smallest
relevant limit.
files_free 22 uint64 READ Free file slots on
the file system
containing this
object - this should
be the smallest
relevant limit.
files_total 23 uint64 READ Total file slots on
the file system
containing this
object.
fs_locations 24 fs_locations READ Locations where this
file system may be
found. If the server
returns NFS4ERR_MOVED
as an error, this
attribute must be
supported.
hidden 25 boolean R/W Is file considered
hidden with respect
to the WIN32 API?
homogeneous 26 boolean READ Whether or not this
object's file system
is homogeneous, i.e.
are per file system
attributes the same
for all file system's
objects.
maxfilesize 27 uint64 READ Maximum supported
file size for the
file system of this
object.
maxlink 28 uint32 READ Maximum number of
links for this
object.
maxname 29 uint32 READ Maximum filename size
supported for this
object.
maxread 30 uint64 READ Maximum read size
supported for this
object.
maxwrite 31 uint64 READ Maximum write size
supported for this
object. This
attribute SHOULD be
supported if the file
is writable. Lack of
this attribute can
lead to the client
either wasting
bandwidth or not
receiving the best
performance.
mimetype 32 utf8<> R/W MIME body
type/subtype of this
object.
mode 33 mode4 R/W Unix-style permission
bits for this object
(deprecated in favor
of ACLs)
no_trunc 34 boolean READ If a name longer than
name_max is used,
will an error be
returned or will the
name be truncated?
numlinks 35 uint32 READ Number of hard links
to this object.
owner 36 utf8<> R/W The string name of
the owner of this
object.
owner_group 37 utf8<> R/W The string name of
the group ownership
of this object.
quota_avail_hard 38 uint64 READ For definition see
"Quota Attributes"
section below.
quota_avail_soft 39 uint64 READ For definition see
"Quota Attributes"
section below.
quota_used 40 uint64 READ For definition see
"Quota Attributes"
section below.
rawdev 41 specdata4 READ Raw device
identifier. Unix
device major/minor
node information.
space_avail 42 uint64 READ Disk space in bytes
available to this
user on the file
system containing
this object - this
should be the
smallest relevant
limit.
space_free 43 uint64 READ Free disk space in
bytes on the file
system containing
this object - this
should be the
smallest relevant
limit.
space_total 44 uint64 READ Total disk space in
bytes on the file
system containing
this object.
space_used 45 uint64 READ Number of file system
bytes allocated to
this object.
system 46 boolean R/W Is this file a system
file with respect to
the WIN32 API?
time_access 47 nfstime4 READ The time of last
access to the object.
time_access_set 48 settime4 WRITE Set the time of last
access to the object.
SETATTR use only.
time_backup 49 nfstime4 R/W The time of last
backup of the object.
time_create 50 nfstime4 R/W The time of creation
of the object. This
attribute does not
have any relation to
the traditional Unix
file attribute
"ctime" or "change
time".
time_delta 51 nfstime4 READ Smallest useful
server time
granularity.
time_metadata 52 nfstime4 R/W The time of last
meta-data
modification of the
object.
time_modify 53 nfstime4 READ The time of last
modification to the
object.
time_modify_set 54 settime4 WRITE Set the time of last
modification to the
object. SETATTR use
only.
5.6. Interpreting owner and owner_group
The recommended attributes "owner" and "owner_group" are represented
in terms of a UTF-8 string. To avoid a representation that is tied
to a particular underlying implementation at the client or server,
the use of the UTF-8 string has been chosen. Note that section 6.1
of [RFC2624] provides additional rationale. It is expected that the
client and server will have their own local representation of owner
and owner_group that is used for local storage or presentation to the
end user. Therefore, it is expected that when these attributes are
transferred between the client and server that the local
representation is translated to a syntax of the form
"user@dns_domain". This will allow for a client and server that do
not use the same local representation the ability to translate to a
common syntax that can be interpreted by both.
The translation is not specified as part of the protocol. This
allows various solutions to be employed. For example, a local
translation table may be consulted that maps between a numeric id to
the user@dns_domain syntax. A name service may also be used to
accomplish the translation. The "dns_domain" portion of the owner
string is meant to be a DNS domain name. For example, user@ietf.org.
In the case where there is no translation available to the client or
server, the attribute value must be constructed without the "@".
Therefore, the absence of the @ from the owner or owner_group
attribute signifies that no translation was available and the
receiver of the attribute should not place any special meaning with
the attribute value. Even though the attribute value can not be
translated, it may still be useful. In the case of a client, the
attribute string may be used for local display of ownership.
5.7. Character Case Attributes
With respect to the case_insensitive and case_preserving attributes,
each UCS-4 character (which UTF-8 encodes) has a "long descriptive
name" [RFC1345] which may or may not included the word "CAPITAL" or
"SMALL". The presence of SMALL or CAPITAL allows an NFS server to
implement unambiguous and efficient table driven mappings for case
insensitive comparisons, and non-case-preserving storage. For
general character handling and internationalization issues, see the
section "Internationalization".
5.8. Quota Attributes
For the attributes related to file system quotas, the following
definitions apply:
quota_avail_soft
The value in bytes which represents the amount of additional
disk space that can be allocated to this file or directory
before the user may reasonably be warned. It is understood
that this space may be consumed by allocations to other files
or directories though there is a rule as to which other files
or directories.
quota_avail_hard
The value in bytes which represent the amount of additional
disk space beyond the current allocation that can be allocated
to this file or directory before further allocations will be
refused. It is understood that this space may be consumed by
allocations to other files or directories.
quota_used
The value in bytes which represent the amount of disc space
used by this file or directory and possibly a number of other
similar files or directories, where the set of "similar" meets
at least the criterion that allocating space to any file or
directory in the set will reduce the "quota_avail_hard" of
every other file or directory in the set.
Note that there may be a number of distinct but overlapping
sets of files or directories for which a quota_used value is
maintained. E.g. "all files with a given owner", "all files
with a given group owner". etc.
The server is at liberty to choose any of those sets but should
do so in a repeatable way. The rule may be configured per-
filesystem or may be "choose the set with the smallest quota".
5.9. Access Control Lists
The NFS ACL attribute is an array of access control entries (ACE).
There are various access control entry types. The server is able to
communicate which ACE types are supported by returning the
appropriate value within the aclsupport attribute. The types of ACEs
are defined as follows:
Type Description
_____________________________________________________
ALLOW Explicitly grants the access defined in
acemask4 to the file or directory.
DENY Explicitly denies the access defined in
acemask4 to the file or directory.
AUDIT LOG (system dependent) any access
attempt to a file or directory which
uses any of the access methods specified
in acemask4.
ALARM Generate a system ALARM (system
dependent) when any access attempt is
made to a file or directory for the
access methods specified in acemask4.
The NFS ACE attribute is defined as follows:
typedef uint32_t acetype4;
typedef uint32_t aceflag4;
typedef uint32_t acemask4;
struct nfsace4 {
acetype4 type;
aceflag4 flag;
acemask4 access_mask;
utf8string who;
};
To determine if an ACCESS or OPEN request succeeds each nfsace4 entry
is processed in order by the server. Only ACEs which have a "who"
that matches the requester are considered. Each ACE is processed
until all of the bits of the requester's access have been ALLOWED.
Once a bit (see below) has been ALLOWED by an ACCESS_ALLOWED_ACE, it
is no longer considered in the processing of later ACEs. If an
ACCESS_DENIED_ACE is encountered where the requester's mode still has
unALLOWED bits in common with the "access_mask" of the ACE, the
request is denied.
The bitmask constants used to represent the above definitions within
the aclsupport attribute are as follows:
const ACL4_SUPPORT_ALLOW_ACL = 0x00000001;
const ACL4_SUPPORT_DENY_ACL = 0x00000002;
const ACL4_SUPPORT_AUDIT_ACL = 0x00000004;
const ACL4_SUPPORT_ALARM_ACL = 0x00000008;
5.9.1. ACE type
The semantics of the "type" field follow the descriptions provided
above.
The bitmask constants used for the type field are as follows:
const ACE4_ACCESS_ALLOWED_ACE_TYPE = 0x00000000;
const ACE4_ACCESS_DENIED_ACE_TYPE = 0x00000001;
const ACE4_SYSTEM_AUDIT_ACE_TYPE = 0x00000002;
const ACE4_SYSTEM_ALARM_ACE_TYPE = 0x00000003;
5.9.2. ACE flag
The "flag" field contains values based on the following descriptions.
ACE4_FILE_INHERIT_ACE
Can be placed on a directory and indicates that this ACE should be
added to each new non-directory file created.
ACE4_DIRECTORY_INHERIT_ACE
Can be placed on a directory and indicates that this ACE should be
added to each new directory created.
ACE4_INHERIT_ONLY_ACE
Can be placed on a directory but does not apply to the directory,
only to newly created files/directories as specified by the above two
flags.
ACE4_NO_PROPAGATE_INHERIT_ACE
Can be placed on a directory. Normally when a new directory is
created and an ACE exists on the parent directory which is marked
ACL4_DIRECTORY_INHERIT_ACE, two ACEs are placed on the new directory.
One for the directory itself and one which is an inheritable ACE for
newly created directories. This flag tells the server to not place
an ACE on the newly created directory which is inheritable by
subdirectories of the created directory.
ACE4_SUCCESSFUL_ACCESS_ACE_FLAG
ACL4_FAILED_ACCESS_ACE_FLAG
Both indicate for AUDIT and ALARM which state to log the event. On
every ACCESS or OPEN call which occurs on a file or directory which
has an ACL that is of type ACE4_SYSTEM_AUDIT_ACE_TYPE or
ACE4_SYSTEM_ALARM_ACE_TYPE, the attempted access is compared to the
ace4mask of these ACLs. If the access is a subset of ace4mask and the
identifier match, an AUDIT trail or an ALARM is generated. By
default this happens regardless of the success or failure of the
ACCESS or OPEN call.
The flag ACE4_SUCCESSFUL_ACCESS_ACE_FLAG only produces the AUDIT or
ALARM if the ACCESS or OPEN call is successful. The
ACE4_FAILED_ACCESS_ACE_FLAG causes the ALARM or AUDIT if the ACCESS
or OPEN call fails.
ACE4_IDENTIFIER_GROUP
Indicates that the "who" refers to a GROUP as defined under Unix.
The bitmask constants used for the flag field are as follows:
const ACE4_FILE_INHERIT_ACE = 0x00000001;
const ACE4_DIRECTORY_INHERIT_ACE = 0x00000002;
const ACE4_NO_PROPAGATE_INHERIT_ACE = 0x00000004;
const ACE4_INHERIT_ONLY_ACE = 0x00000008;
const ACE4_SUCCESSFUL_ACCESS_ACE_FLAG = 0x00000010;
const ACE4_FAILED_ACCESS_ACE_FLAG = 0x00000020;
const ACE4_IDENTIFIER_GROUP = 0x00000040;
5.9.3. ACE Access Mask
The access_mask field contains values based on the following:
Access Description
_______________________________________________________________
READ_DATA Permission to read the data of the file
LIST_DIRECTORY Permission to list the contents of a
directory
WRITE_DATA Permission to modify the file's data
ADD_FILE Permission to add a new file to a
directory
APPEND_DATA Permission to append data to a file
ADD_SUBDIRECTORY Permission to create a subdirectory to a
directory
READ_NAMED_ATTRS Permission to read the named attributes
of a file
WRITE_NAMED_ATTRS Permission to write the named attributes
of a file
EXECUTE Permission to execute a file
DELETE_CHILD Permission to delete a file or directory
within a directory
READ_ATTRIBUTES The ability to read basic attributes
(non-acls) of a file
WRITE_ATTRIBUTES Permission to change basic attributes
(non-acls) of a file
DELETE Permission to Delete the file
READ_ACL Permission to Read the ACL
WRITE_ACL Permission to Write the ACL
WRITE_OWNER Permission to change the owner
SYNCHRONIZE Permission to access file locally at the
server with synchronous reads and writes
The bitmask constants used for the access mask field are as follows:
const ACE4_READ_DATA = 0x00000001;
const ACE4_LIST_DIRECTORY = 0x00000001;
const ACE4_WRITE_DATA = 0x00000002;
const ACE4_ADD_FILE = 0x00000002;
const ACE4_APPEND_DATA = 0x00000004;
const ACE4_ADD_SUBDIRECTORY = 0x00000004;
const ACE4_READ_NAMED_ATTRS = 0x00000008;
const ACE4_WRITE_NAMED_ATTRS = 0x00000010;
const ACE4_EXECUTE = 0x00000020;
const ACE4_DELETE_CHILD = 0x00000040;
const ACE4_READ_ATTRIBUTES = 0x00000080;
const ACE4_WRITE_ATTRIBUTES = 0x00000100;
const ACE4_DELETE = 0x00010000;
const ACE4_READ_ACL = 0x00020000;
const ACE4_WRITE_ACL = 0x00040000;
const ACE4_WRITE_OWNER = 0x00080000;
const ACE4_SYNCHRONIZE = 0x00100000;
5.9.4. ACE who
There are several special identifiers ("who") which need to be
understood universally. Some of these identifiers cannot be
understood when an NFS client accesses the server, but have meaning
when a local process accesses the file. The ability to display and
modify these permissions is permitted over NFS.
Who Description
_______________________________________________________________
"OWNER" The owner of the file.
"GROUP" The group associated with the file.
"EVERYONE" The world.
"INTERACTIVE" Accessed from an interactive terminal.
"NETWORK" Accessed via the network.
"DIALUP" Accessed as a dialup user to the server.
"BATCH" Accessed from a batch job.
"ANONYMOUS" Accessed without any authentication.
"AUTHENTICATED" Any authenticated user (opposite of
ANONYMOUS)
"SERVICE" Access from a system service.
To avoid conflict, these special identifiers are distinguish by an
appended "@" and should appear in the form "xxxx@" (note: no domain
name after the "@"). For example: ANONYMOUS@.
6. File System Migration and Replication
With the use of the recommended attribute "fs_locations", the NFS
version 4 server has a method of providing file system migration or
replication services. For the purposes of migration and replication,
a file system will be defined as all files that share a given fsid
(both major and minor values are the same).
The fs_locations attribute provides a list of file system locations.
These locations are specified by providing the server name (either
DNS domain or IP address) and the path name representing the root of
the file system. Depending on the type of service being provided,
the list will provide a new location or a set of alternate locations
for the file system. The client will use this information to
redirect its requests to the new server.
6.1. Replication
It is expected that file system replication will be used in the case
of read-only data. Typically, the file system will be replicated on
two or more servers. The fs_locations attribute will provide the
list of these locations to the client. On first access of the file
system, the client should obtain the value of the fs_locations
attribute. If, in the future, the client finds the server
unresponsive, the client may attempt to use another server specified
by fs_locations.
If applicable, the client must take the appropriate steps to recover
valid filehandles from the new server. This is described in more
detail in the following sections.
6.2. Migration
File system migration is used to move a file system from one server
to another. Migration is typically used for a file system that is
writable and has a single copy. The expected use of migration is for
load balancing or general resource reallocation. The protocol does
not specify how the file system will be moved between servers. This
server-to-server transfer mechanism is left to the server
implementor. However, the method used to communicate the migration
event between client and server is specified here.
Once the servers participating in the migration have completed the
move of the file system, the error NFS4ERR_MOVED will be returned for
subsequent requests received by the original server. The
NFS4ERR_MOVED error is returned for all operations except GETATTR.
Upon receiving the NFS4ERR_MOVED error, the client will obtain the
value of the fs_locations attribute. The client will then use the
contents of the attribute to redirect its requests to the specified
server. To facilitate the use of GETATTR, operations such as PUTFH
must also be accepted by the server for the migrated file system's
filehandles. Note that if the server returns NFS4ERR_MOVED, the
server MUST support the fs_locations attribute.
If the client requests more attributes than just fs_locations, the
server may return fs_locations only. This is to be expected since
the server has migrated the file system and may not have a method of
obtaining additional attribute data.
The server implementor needs to be careful in developing a migration
solution. The server must consider all of the state information
clients may have outstanding at the server. This includes but is not
limited to locking/share state, delegation state, and asynchronous
file writes which are represented by WRITE and COMMIT verifiers. The
server should strive to minimize the impact on its clients during and
after the migration process.
6.3. Interpretation of the fs_locations Attribute
The fs_location attribute is structured in the following way:
struct fs_location {
utf8string server<>;
pathname4 rootpath;
};
struct fs_locations {
pathname4 fs_root;
fs_location locations<>;
};
The fs_location struct is used to represent the location of a file
system by providing a server name and the path to the root of the
file system. For a multi-homed server or a set of servers that use
the same rootpath, an array of server names may be provided. An
entry in the server array is an UTF8 string and represents one of a
traditional DNS host name, IPv4 address, or IPv6 address. It is not
a requirement that all servers that share the same rootpath be listed
in one fs_location struct. The array of server names is provided for
convenience. Servers that share the same rootpath may also be listed
in separate fs_location entries in the fs_locations attribute.
The fs_locations struct and attribute then contains an array of
locations. Since the name space of each server may be constructed
differently, the "fs_root" field is provided. The path represented
by fs_root represents the location of the file system in the server's
name space. Therefore, the fs_root path is only associated with the
server from which the fs_locations attribute was obtained. The
fs_root path is meant to aid the client in locating the file system
at the various servers listed.
As an example, there is a replicated file system located at two
servers (servA and servB). At servA the file system is located at
path "/a/b/c". At servB the file system is located at path "/x/y/z".
In this example the client accesses the file system first at servA
with a multi-component lookup path of "/a/b/c/d". Since the client
used a multi-component lookup to obtain the filehandle at "/a/b/c/d",
it is unaware that the file system's root is located in servA's name
space at "/a/b/c". When the client switches to servB, it will need
to determine that the directory it first referenced at servA is now
represented by the path "/x/y/z/d" on servB. To facilitate this, the
fs_locations attribute provided by servA would have a fs_root value
of "/a/b/c" and two entries in fs_location. One entry in fs_location
will be for itself (servA) and the other will be for servB with a
path of "/x/y/z". With this information, the client is able to
substitute "/x/y/z" for the "/a/b/c" at the beginning of its access
path and construct "/x/y/z/d" to use for the new server.
6.4. Filehandle Recovery for Migration or Replication
Filehandles for file systems that are replicated or migrated
generally have the same semantics as for file systems that are not
replicated or migrated. For example, if a file system has persistent
filehandles and it is migrated to another server, the filehandle
values for the file system will be valid at the new server.
For volatile filehandles, the servers involved likely do not have a
mechanism to transfer filehandle format and content between
themselves. Therefore, a server may have difficulty in determining
if a volatile filehandle from an old server should return an error of
NFS4ERR_FHEXPIRED. Therefore, the client is informed, with the use
of the fh_expire_type attribute, whether volatile filehandles will
expire at the migration or replication event. If the bit
FH4_VOL_MIGRATION is set in the fh_expire_type attribute, the client
must treat the volatile filehandle as if the server had returned the
NFS4ERR_FHEXPIRED error. At the migration or replication event in
the presence of the FH4_VOL_MIGRATION bit, the client will not
present the original or old volatile file handle to the new server.
The client will start its communication with the new server by
recovering its filehandles using the saved file names.
7. NFS Server Name Space
7.1. Server Exports
On a UNIX server the name space describes all the files reachable by
pathnames under the root directory or "/". On a Windows NT server
the name space constitutes all the files on disks named by mapped
disk letters. NFS server administrators rarely make the entire
server's file system name space available to NFS clients. More often
portions of the name space are made available via an "export"
feature. In previous versions of the NFS protocol, the root
filehandle for each export is obtained through the MOUNT protocol;
the client sends a string that identifies the export of name space
and the server returns the root filehandle for it. The MOUNT