STAT(5) File Formats Manual STAT(5)
stat, wstat - inquire or change file attributes
Tstat tag fid
Rstat tag fid stat
Twstat tag fid stat
Rwstat tag fid
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 file name; must be / if the file is the root directory
of the server
uid owner name
gid group name
qid.path the file server's identification for the file
qid.vers version number for given path
mode permissions and flags
atime last access time
mtime last modification time
length length of file in bytes
type for kernel use
dev 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 fol-
lowing: 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
A read of a directory yields an integral number of directory entries in
the machine independent encoding given above (see read(5)).
Stat messages are generated by fstat and stat.
Wstat messages are generated by fwstat and wstat.