NAME

stat, wstat − inquire or change file attributes

SYNOPSIS

Tstat tag[2] fid[2]
Rstat tag[2] fid[2] stat[116]

Twstat tag[2] fid[2] stat[116]
Rwstat tag[2] fid[2]

DESCRIPTION

The ­stat transaction inquires about the file identified by fid. The reply will contain a 116-byte (DIRLEN in <libc.h>) machine-independent directory entry laid out as follows:

name[28] file name

uid[28] owner name

gid[28] group name

qid.path[4] the file server’s identification for the file

qid.vers[4] version number for given path

mode[4] permissions and flags

atime[4] last access time

mtime[4] last modification time

length[8] length of file in bytes

type[2] for kernel use

dev[2] for kernel use

Integers in this encoding are in little-endian order (least significant byte first).  The ­convM2D and ­convD2M routines (see fcall(2)) convert between directory entries and C structs. 

This encoding may be turned into a machine dependent ­Dir structure (see stat(2)) using routines defined in fcall(2).

The ­mode contains permission bits as described in intro(5) and the following: ­0x80000000 (this file is a directory), ­0x40000000 (append only), ­0x20000000 (exclusive use).  Writes to append-only files always place their data at the end of the file; the ­offset in the ­read or ­write message is ignored.  Exclusive use files may be open for I/O by only one fid at a time across all clients of the server.  If a second open is attempted, it draws an error.  Servers may implement a timeout on the lock on an exclusive use file: if the fid holding the file open has been unused for an extended period (of order at least minutes), it is reasonable to break the lock and deny the initial fid further I/O. 

The two time fields are measured in seconds since the epoch (Jan 1 00:00 1970 local time).  The ­mtime field reflects the time of the last change of content.  For a plain file, ­mtime is the time of the most recent create, ­open with truncation, or write; for a directory it is the time of the most recent remove, create, or ­wstat of a file in the directory.  Similarly, the ­atime field records the last ­read of the contents; also it is set whenever ­mtime is set.  In addition, for a directory, it is set by an attach, walk, or create, all whether successful or not. 

The ­length records the number of bytes in the file.  Directories and most files representing devices have a conventional length of 0. 

The ­stat request requires no special permissions. 

The ­wstat request can change some of the file status information.  The ­name can be changed by anyone with write permission in the parent directory; it is an error to change the name to that of an existing file.  The ­mode can be changed by the owner of the file or the group leader of the file’s current group.  The directory bit cannot be changed by a wstat; the other defined permission and mode bits can.  The ­gid can be changed: by the owner if also a member of the new group; or by the group leader of the file’s current group if also leader of the new group (see intro(5) for more information about permissions and users(6) for users and groups). None of the other data can be altered by a wstat.  In particular, there is no way to change the owner of a file. 

A ­read of a directory yields an integral number of directory entries in the machine independent encoding given above (see read(5)).

ENTRY POINTS

­Stat messages are generated by ­fstat and ­stat. 

­Wstat messages are generated by ­fwstat and ­wstat. 

Plan 9  —  January 03, 1993