The TCP/IP Guide - NFS Server Procedures and Operations

It is common that a client may want to perform multiple actions on a file: several consecutive reads, for example. One of the problems with the server procedure system in NFSv2 and NFSv3 is that each client action required a separate procedure call. This was somewhat inefficient, especially when NFS was used over a high-latency link.

To improve the efficiency of server procedures, NFS version 4 makes a significant change to the way that server procedures are implemented. Instead of each client action being a separate procedure, a single procedure called compound is defined. Within this “compound” procedure, a large number of server operations are encapsulated. These are all sent as a single unit and the server interprets and follows the instructions in each operation in sequence.

This change means there are actually only two RPC procedures in NFSv4, as shown in Table 183.

All the real client actions are defined as operations within the compound procedure, as shown in Table 184. You'll notice that the number of NFSv4 operations is much larger than the number of procedures in NFSv2 and NFSv3. This is due both to the added features in version 4 and the fact that NFSv4 incorporates functions formerly performed by the separate Mount protocol into NFS itself.

**Table 184: NFS Version 4 Server Operations**
Operation #	Operation Name	Operation Summary	Description
3	access	Check Access Rights	Determines the access rights a user has for an object.
4	close	Close File	Closes a file.
5	commit	Commit Cached Data	Flushes any data that the server is holding in a write cache to storage, to ensure that any pending data is permanently recorded.
6	create	Create A Non-Regular File Object	This is similar to the mknod procedure in NFSv3; it creates a “non-regular” (special) object file. (Regular files are created using the open operation.)
7	delepurge	Purge Delegations Awaiting Recovery	NFSv4 has a feature where a server may delegate to a client responsibility for certain files. This operation removes delegations awaiting recovery from a client.
8	delegreturn	Return Delegation	Returns a delegation from a client to the server that granted it.
9	getattr	Get Attributes	Obtains the attributes for a file.
10	getfh	Get Current Filehandle	Returns a file handle, which is a logical object used to allow access to a file.
11	link	Create Link To A File	Creates a “hard' (non-symbolic) link to a file.
12	lock	Create Lock	Creates a lock on a file. Locks are used to manage access to a file, for example, to prevent two clients from trying to write to a file simultaneously and thus corrupting it.
13	lockt	Test For Lock	Tests for the existence of a lock on an object and returns information about it.
14	locku	Unlock File	Removes a lock previously created on a file.
15	lookup	Lookup Filename	Looks up or finds a file.
16	lookupp	Lookup Parent Directory	Returns the filehandle of an object's parent directory.
17	nverify	Verify Difference In Attributes	Checks to see if attributes have changed on a file.
18	open	Open A Regular File	Opens a file.
19	openattr	Open Named Attribute Directory	Opens an attribute directory associated with a file.
20	open_confirm	Confirm Open	Confirms information related to an opened file.
21	open_ downgrade	Reduce Open File Access	Adjusts the access rights for a file that is already open.
22	putfh	Set Current Filehandle	Replaces one filehandle with another.
23	putpubfh	Set Public Filehandle	Sets the current filehandle to be the “public” filehandle of the server. This may or may not be the same as the root filehandle (see below).
24	putrootfh	Set Root Filehandle	Sets the current filehandle to be the root of the server's file system.
25	read	Read From File	Reads data from a file.
26	readdir	Read Directory	Reads the contents of a directory.
27	readlink	Read Symbolic Link	Reads the name of a file specified using a symbolic link.
28	remove	Remove Filesystem Object	Removes (deletes) an object.
29	rename	Rename Directory Entry	Changes the name of an object.
30	renew	Renew A Lease	Renews an NFS delegation made by a server. (Note that these leases have nothing to do with DHCP leases!)
31	restorefh	Restore Saved Filehandle	Allows a filehandle previously saved to be made the current filehandle.
32	savefh	Save Current Filehandle	Allows a filehandle to be saved so it can later be restored when needed.
33	secinfo	Obtain Available Security	Retrieves NFS security information.
34	setattr	Set Attributes	Changes one or more attributes of a file.
35	setclientid	Negotiate Clientid	Allows a client to communicate information to the server regarding how the client wants to use NFS.
36	setclientid_ confirm	Confirm Clientid	Used to confirm the results of a previous negotiation using setclientid.
37	verify	Verify Same Attributes	Allows a client to verify certain attributes before proceeding with a particular action.
38	write	Write To File	Writes data to a file.
39	release_ lockowner	Release Lockowner State	Used by a client to tell a server to release certain information related to file locks.
10044	illegal	Illegal Operation	A “placeholder” (dummy) operation used to support error reporting when an invalid operation is used in a request from a client.

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