.TH STAT 2
.SH NAME
stat, fstat, wstat, fwstat, dirstat, dirfstat, dirwstat, dirfwstat \- get and put file status
.SH SYNOPSIS
.B #include <u.h>
.br
.B #include <libc.h>
.PP
.B
int stat(char *name, char *edir)
.PP
.B
int fstat(int fd, char *edir)
.PP
.B
int wstat(char *name, char *edir)
.PP
.B
int fwstat(int fd, char *edir)
.PP
.B
int dirstat(char *name, Dir *dir)
.PP
.B
int dirfstat(int fd, Dir *dir)
.PP
.B
int dirwstat(char *name, Dir *dir)
.PP
.B
int dirfwstat(int fd, Dir *dir)
.SH DESCRIPTION
Given a file's
.IR name ,
or an open file descriptor
.IR fd ,
these routines retrieve or modify file status information.
.IR Stat ,
.IR fstat ,
.IR wstat ,
and
.I fwstat
are the system calls; they deal with machine-independent
.IR "directory entries" .
Their format is defined by
.IR stat (5).
.I Stat
and
.I fstat
retrieve information about
.I name
or
.I fd
into
.IR edir ,
a buffer of length
.BR DIRLEN ,
defined in
.BR <libc.h> .
.I Wstat
and
.I fwstat
write information back, thus changing file attributes according to
.IR edir .
.PP
.IR Dirstat ,
.IR dirfstat ,
.IR dirwstat ,
and
.I dirfwstat
are the same as their counterparts, except that they
operate on
.I Dir
structures:
.IP
.EX
.ta 6n +\w'Length; 'u +\w'name[NAMELEN];   'u
typedef
struct Dir {
	char	name[NAMELEN];	/* last element of path */
	char	uid[NAMELEN];	/* owner name */
	char	gid[NAMELEN];	/* group name */
	Qid	qid;	/* unique id from server */
	long	mode;	/* permissions */
	long	atime;	/* last read time */
	long	mtime;	/* last write time */
	Length;		/* file length: see <u.h> */
	ushort	type;	/* server type */
	ushort	dev;	/* server subtype */
} Dir;
.EE
.PP
This structure,
the
.I Qid
structure,
.BR NAMELEN ,
and
.B DIRLEN
are defined in
.BR <libc.h> .
For historical reasons,
the
.B Length
structure, defined in
.BR </$objtype/u.h> ,
is a structure with a single
.B vlong
element,
.BR length .
If the file resides on permanent storage and is not a directory,
the length returned by
.I stat
is the number of bytes in the file.
For directories, the length returned is zero.
For files that are streams (e.g., pipes and network connections),
the length is the number of bytes that can be read without blocking.
.PP
Each file is the responsibility of some
.IR server :
it could be a file server, a kernel device, or a user process.
.B Type
identifies the server type, and
.B dev
says which of a group of servers of the same type is the one
responsible for this file.
.B Qid
is a structure containing
.B path
and
.B vers
fields, each an
.B unsigned
.BR long :
.B path
is guaranteed to be
unique among all path names currently on the file server, and
.B vers
changes each time the file is modified.
Thus, if two files have the same
.BR type ,
.BR dev ,
and
.B qid
they are the same file.
.PP
The bits in
.B mode
are defined by
.PP
.ta 6n +\w'\fL0x80000000   'u
.nf
\fL	0x80000000\fP	directory
\fL	0x40000000\fP	append only
\fL	0x20000000\fP	exclusive use (locked)

\fL	      0400\fP	read permission by owner
\fL	      0200\fP	write permission by owner
\fL	      0100\fP	execute permission (search on directory) by owner
\fL	      0070\fP	read, write, execute (search) by group
\fL	      0007\fP	read, write, execute (search) by others
.fi
.PP
There are constants defined in
.B <libc.h>
for these bits:
.BR CHDIR ,
.BR CHAPPEND ,
and
.B CHEXCL
for the first three; and
.BR CHREAD ,
.BR CHWRITE ,
and
.B CHEXEC
for the read, write, and execute bits for others.
.PP
The two time fields are measured in seconds since the epoch
(Jan 1 00:00 1970 GMT).
.B Mtime
is the time of the last change of content.
Similarly,
.B atime
is set whenever the contents are accessed;
also, it is set whenever
.B mtime
is set.
.PP
.B Uid
and
.B gid
are the names of the owner and group of the file.
Groups are also users, but each server is free to associate
a list of users with any user name
.IR g ,
and that list is the
set of users in the group
.IR g .
When an initial attachment is made to a server,
the user string in the process group is communicated to the server.
Thus, the server knows, for any given file access, whether the accessing
process is the owner of, or in the group of, the file.
This selects which sets of three bits in
.B mode
is used to check permissions.
.PP
Only some of the fields may be changed with the
.I wstat
calls.
The
.B name
can be changed by anyone with write permission in the parent directory.
The
.B mode
and
.B mtime
can be changed by the owner or the group leader of the file's current
group.
The
.B gid
can be changed by the owner if he or she is a member of the new group.
The
.B gid
can be changed by the group leader of the file's current group
if he or she is the leader of the new group.
(See
.IR intro (5)
for permission information, and
.IR users (6)
for user and group information).
.SH SOURCE
.TF /sys/src/libc/9syscall
.TP
.B /sys/src/libc/9syscall
for the
.RB non- dir
routines
.TP
.B /sys/src/libc/9sys
for the routines prefixed
.L dir
.SH SEE ALSO
.IR intro (2),
.IR fcall (2),
.IR dirread (2),
.IR stat (5)
.SH DIAGNOSTICS
All these functions return 0 on success, -1 on error, and set
.IR errstr .