STAT(5) File Formats Manual STAT(5)
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; must be / if the file is the root directory of the server
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)) con-
vert 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, as is the OTRUNC bit in an open. 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 GMT). 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 and mtime 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.
STAT(5)