rfc1094.txt
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empty. NFSERR_DQUOT Disk quota exceeded. The client's disk quota on the server has been exceeded. NFSERR_STALE The "fhandle" given in the arguments was invalid. That is, the file referred to by that file handle no longer exists, or access to it has been revoked. NFSERR_WFLUSH The server's write cache used in the "WRITECACHE" call got flushed to disk.Sun Microsystems, Inc. [Page 14] RFC 1094 NFS: Network File System March 19892.3.2. ftype enum ftype { NFNON = 0, NFREG = 1, NFDIR = 2, NFBLK = 3, NFCHR = 4, NFLNK = 5 }; The enumeration "ftype" gives the type of a file. The type NFNON indicates a non-file, NFREG is a regular file, NFDIR is a directory, NFBLK is a block-special device, NFCHR is a character- special device, and NFLNK is a symbolic link.2.3.3. fhandle typedef opaque fhandle[FHSIZE]; The "fhandle" is the file handle passed between the server and the client. All file operations are done using file handles to refer to a file or directory. The file handle can contain whatever information the server needs to distinguish an individual file.2.3.4. timeval struct timeval { unsigned int seconds; unsigned int useconds; }; The "timeval" structure is the number of seconds and microseconds since midnight January 1, 1970, Greenwich Mean Time. It is used to pass time and date information.2.3.5. fattr struct fattr { ftype type; unsigned int mode; unsigned int nlink; unsigned int uid; unsigned int gid; unsigned int size; unsigned int blocksize; unsigned int rdev; unsigned int blocks;Sun Microsystems, Inc. [Page 15] RFC 1094 NFS: Network File System March 1989 unsigned int fsid; unsigned int fileid; timeval atime; timeval mtime; timeval ctime; }; The "fattr" structure contains the attributes of a file; "type" is the type of the file; "nlink" is the number of hard links to the file (the number of different names for the same file); "uid" is the user identification number of the owner of the file; "gid" is the group identification number of the group of the file; "size" is the size in bytes of the file; "blocksize" is the size in bytes of a block of the file; "rdev" is the device number of the file if it is type NFCHR or NFBLK; "blocks" is the number of blocks the file takes up on disk; "fsid" is the file system identifier for the filesystem containing the file; "fileid" is a number that uniquely identifies the file within its filesystem; "atime" is the time when the file was last accessed for either read or write; "mtime" is the time when the file data was last modified (written); and "ctime" is the time when the status of the file was last changed. Writing to the file also changes "ctime" if the size of the file changes. "Mode" is the access mode encoded as a set of bits. Notice that the file type is specified both in the mode bits and in the file type. This is really a bug in the protocol and will be fixed in future versions. The descriptions given below specify the bit positions using octal numbers. 0040000 This is a directory; "type" field should be NFDIR. 0020000 This is a character special file; "type" field should be NFCHR. 0060000 This is a block special file; "type" field should be NFBLK. 0100000 This is a regular file; "type" field should be NFREG. 0120000 This is a symbolic link file; "type" field should be NFLNK. 0140000 This is a named socket; "type" field should be NFNON. 0004000 Set user id on execution. 0002000 Set group id on execution. 0001000 Save swapped text even after use. 0000400 Read permission for owner. 0000200 Write permission for owner. 0000100 Execute and search permission for owner. 0000040 Read permission for group. 0000020 Write permission for group. 0000010 Execute and search permission for group.Sun Microsystems, Inc. [Page 16] RFC 1094 NFS: Network File System March 1989 0000004 Read permission for others. 0000002 Write permission for others. 0000001 Execute and search permission for others. Notes: The bits are the same as the mode bits returned by the stat(2) system call in UNIX. The file type is specified both in the mode bits and in the file type. This is fixed in future versions. The "rdev" field in the attributes structure is an operating system specific device specifier. It will be removed and generalized in the next revision of the protocol.2.3.6. sattr struct sattr { unsigned int mode; unsigned int uid; unsigned int gid; unsigned int size; timeval atime; timeval mtime; }; The "sattr" structure contains the file attributes which can be set from the client. The fields are the same as for "fattr" above. A "size" of zero means the file should be truncated. A value of -1 indicates a field that should be ignored.2.3.7. filename typedef string filename<MAXNAMLEN>; The type "filename" is used for passing file names or pathname components.2.3.8. path typedef string path<MAXPATHLEN>; The type "path" is a pathname. The server considers it as a string with no internal structure, but to the client it is the name of a node in a filesystem tree.2.3.9. attrstat union attrstat switch (stat status) { case NFS_OK:Sun Microsystems, Inc. [Page 17] RFC 1094 NFS: Network File System March 1989 fattr attributes; default: void; }; The "attrstat" structure is a common procedure result. It contains a "status" and, if the call succeeded, it also contains the attributes of the file on which the operation was done.2.3.10. diropargs struct diropargs { fhandle dir; filename name; }; The "diropargs" structure is used in directory operations. The "fhandle" "dir" is the directory in which to find the file "name". A directory operation is one in which the directory is affected.2.3.11. diropres union diropres switch (stat status) { case NFS_OK: struct { fhandle file; fattr attributes; } diropok; default: void; }; The results of a directory operation are returned in a "diropres" structure. If the call succeeded, a new file handle "file" and the "attributes" associated with that file are returned along with the "status".3. NFS IMPLEMENTATION ISSUES The NFS protocol was designed to allow different operating systems to share files. However, since it was designed in a UNIX environment, many operations have semantics similar to the operations of the UNIX file system. This section discusses some of the implementation- specific details and semantic issues.3.1. Server/Client Relationship The NFS protocol is designed to allow servers to be as simple andSun Microsystems, Inc. [Page 18] RFC 1094 NFS: Network File System March 1989 general as possible. Sometimes the simplicity of the server can be a problem, if the client wants to implement complicated filesystem semantics. For example, some operating systems allow removal of open files. A process can open a file and, while it is open, remove it from the directory. The file can be read and written as long as the process keeps it open, even though the file has no name in the filesystem. It is impossible for a stateless server to implement these semantics. The client can do some tricks such as renaming the file on remove, and only removing it on close. We believe that the server provides enough functionality to implement most file system semantics on the client. Every NFS client can also potentially be a server, and remote and local mounted filesystems can be freely intermixed. This leads to some interesting problems when a client travels down the directory tree of a remote filesystem and reaches the mount point on the server for another remote filesystem. Allowing the server to follow the second remote mount would require loop detection, server lookup, and user revalidation. Instead, we decided not to let clients cross a server's mount point. When a client does a LOOKUP on a directory on which the server has mounted a filesystem, the client sees the underlying directory instead of the mounted directory. For example, if a server has a file system called "/usr" and mounts another file system on "/usr/src", if a client mounts "/usr", it does NOT see the mounted version of "/usr/src". A client could do remote mounts that match the server's mount points to maintain the server's view. In this example, the client would also have to mount "/usr/src" in addition to "/usr", even if they are from the same server.3.2. Pathname Interpretation There are a few complications to the rule that pathnames are always parsed on the client. For example, symbolic links could have different interpretations on different clients. Another common problem for non-UNIX implementations is the special interpretation of the pathname ".." to mean the parent of a given directory. The next revision of the protocol uses an explicit flag to indicate the parent instead.3.3. Permission Issues The NFS protocol, strictly speaking, does not define the permission checking used by servers. However, it is expected that a server will do normal operating system permission checking using AUTH_UNIX styleSun Microsystems, Inc. [Page 19] RFC 1094 NFS: Network File System March 1989 authentication as the basis of its protection mechanism. The server gets the client's effective "uid", effective "gid", and groups on each call and uses them to check permission. There are various problems with this method that can been resolved in interesting ways. Using "uid" and "gid" implies that the client and server share the same "uid" list. Every server and client pair must have the same mapping from user to "uid" and from group to "gid". Since every client can also be a server, this tends to imply that the whole network shares the same "uid/gid" space. AUTH_DES (and the next revision of the NFS protocol) uses string names instead of numbers, but there are still complex problems to be solved. Another problem arises due to the usually stateful open operation. Most operating systems check permission at open time, and then check that the file is open on each read and write request. With stateless servers, the server has no idea that the file is open and must do permission checking on each read and write call. On a local filesystem, a user can open a file and then change the permissions so that no one is allowed to touch it, but will still be able to write to the file because it is open. On a remote filesystem, by contrast, the write would fail. To get around this problem, the server's permission checking algorithm should allow the owner of a file to access it regardless of the permission setting. A similar problem has to do with paging in from a file over the network. The operating system usually checks for execute permission before opening a file for demand paging, and then reads blocks from the open file. The file may not have read permission, but after it is opened it does not matter. An NFS server can not tell the difference between a normal file read and a demand page-in read. To make this work, the server allows reading of files if the "uid" given in the call has either execute or read permission on the file. In most operating systems, a particular user (on UNIX, the user ID zero) has access to all files no matter what permission and ownership they have. This "super-user" permission may not be allowed on the server, since anyone who can become super-user on their workstation could gain access to all remote files. The UNIX server by default maps user id 0 to -2 before doing its access checking. This works except for NFS root filesystems, where super-user access cannot be avoided.3.4. RPC Information Authentication The NFS service uses AUTH_UNIX, AUTH_DES, or AUTH_SHORT style authentication, except in the NULL procedure where AUTH_NONE isSun Microsystems, Inc. [Page 20] RFC 1094 NFS: Network File System March 1989 also allowed. Transport Protocols NFS is supported normally on UDP. Port Number The NFS protocol currently uses the UDP port number 2049. This is not an officially assigned port, so later versions of the protocol use the "Portmapping" facility of RPC.3.5. Sizes of XDR Structures⌨️ 快捷键说明
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