STAT(5) 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)) 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, 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.
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STAT(5) STAT(5)
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. Simi-
larly, the atime field records the last read of the con-
tents; 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. Direc-
tories and most files representing devices have a conven-
tional length of 0.
The stat request requires no special permissions.
The wstat request can change some of the file status infor-
mation. The name can be changed by anyone with write per-
mission 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.
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