STAT(2) STAT(2)
NAME
stat, fstat, wstat, fwstat, dirstat, dirfstat, dirwstat,
dirfwstat - get and put file status
SYNOPSIS
#include <u.h>
#include <libc.h>
int stat(char *name, char *edir)
int fstat(int fd, char *edir)
int wstat(char *name, char *edir)
int fwstat(int fd, char *edir)
int dirstat(char *name, Dir *dir)
int dirfstat(int fd, Dir *dir)
int dirwstat(char *name, Dir *dir)
int dirfwstat(int fd, Dir *dir)
DESCRIPTION
Given a file's name, or an open file descriptor fd, these
routines retrieve or modify file status information. Stat,
fstat, wstat, and fwstat are the system calls; they deal
with machine-independent directory entries. Their format is
defined by stat(5). Stat and fstat retrieve information
about name or fd into edir, a buffer of length DIRLEN,
defined in <libc.h>. Wstat and fwstat write information
back, thus changing file attributes according to edir.
Dirstat, dirfstat, dirwstat, and dirfwstat are the same as
their counterparts, except that they operate on Dir struc-
tures:
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 */
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} Dir;
This structure, the Qid structure, NAMELEN, and DIRLEN are
defined in <libc.h>. The Length structure is defined in
</$objtype/u.h>. Length is an unnamed structure (see
2c(1)), which means that its fields are directly accessible;
if the length is known to fit in a long, then use length as
a field name to retrieve it. If the file resides on perma-
nent storage and is not a directory, the length returned by
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.
Each file is the responsibility of some server: it could be
a file server, a kernel device, or a user process. Type
identifies the server type, and dev says which of a group of
servers of the same type is the one responsible for this
file. Qid is a structure containing path and vers fields,
each an unsigned long: path is guaranteed to be unique among
all path names currently on the file server, and vers
changes each time the file is modified. Thus, if two files
have the same type, dev, and qid they are the same file.
The bits in mode are defined by
0x80000000 directory
0x40000000 append only
0x20000000 exclusive use (locked)
0400 read permission by owner
0200 write permission by owner
0100 execute permission (search on directory) by owner
0070 read, write, execute (search) by group
0007 read, write, execute (search) by others
There are constants defined in <libc.h> for these bits:
CHDIR, CHAPPEND, and CHEXCL for the first three; and CHREAD,
CHWRITE, and CHEXEC for the read, write, and execute bits
for others.
The two time fields are measured in seconds since the epoch
(Jan 1 00:00 1970 GMT). Mtime is the time of the last
change of content. Similarly, atime is set whenever the
contents are accessed; also, it is set whenever mtime is
set.
Uid and 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 g, and that
list is the set of users in the group g. When an initial
attachment is made to a server, the user string in the
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process group is communicated to the server. Thus, the
server knows, for any given file access, whether the access-
ing process is the owner of, or in the group of, the file.
This selects which sets of three bits in mode is used to
check permissions.
Only some of the fields may be changed with the wstat calls.
The name can be changed by anyone with write permission in
the parent directory. The mode and mtime can be changed by
the owner or the group leader of the file's current group.
The gid can be changed by the owner if he or she is a member
of the new group. The 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 intro(5) for permission
information, and users(6) for user and group information).
SOURCE
/sys/src/libc/9syscall for the non-dir routines
/sys/src/libc/9sys for the routines prefixed dir
SEE ALSO
intro(2), fcall(2), dirread(2), stat(5)
DIAGNOSTICS
All these functions return 0 on success, -1 on error, and
set errstr.
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