STAT(2)STAT(2)NAME
stat, fstat, wstat, fwstat, dirstat, dirfstat, dirwstat, dirfwstat,
nulldir - get and put file status
SYNOPSIS
#include <u.h>
#include <libc.h>
int stat(char *name, uchar *edir, int nedir)
int fstat(int fd, uchar *edir, int nedir)
int wstat(char *name, uchar *edir, int nedir)
int fwstat(int fd, uchar *edir, int nedir)
Dir* dirstat(char *name)
Dir* dirfstat(int fd)
int dirwstat(char *name, Dir *dir)
int dirfwstat(int fd, Dir *dir)
void nulldir(Dir *d)
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 direc‐
tory entries. Their format is defined by stat(5). Stat and fstat
retrieve information about name or fd into edir, a buffer of length
nedir, defined in <libc.h>. Wstat and fwstat write information back,
thus changing file attributes according to the contents of edir. The
data returned from the kernel includes its leading 16-bit length field
as described in intro(5). For symmetry, this field must also be
present when passing data to the kernel in a call to wstat and fwstat,
but its value is ignored.
Dirstat, dirfstat, dirwstat, and dirfwstat are similar to their coun‐
terparts, except that they operate on Dir structures:
typedef
struct Dir {
/* system-modified data */
uint type; /* server type */
uint dev; /* server subtype */
/* file data */
Qid qid; /* unique id from server */
ulong mode; /* permissions */
ulong atime; /* last read time */
ulong mtime; /* last write time */
vlong length; /* file length: see <u.h> */
char *name; /* last element of path */
char *uid; /* owner name */
char *gid; /* group name */
char *muid; /* last modifier name */
} Dir;
The returned structure is allocated by malloc(2); freeing it also frees
the associated strings.
This structure and the Qid structure are defined in <libc.h>. If the
file resides on permanent 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: path is guaranteed to be unique among all path names cur‐
rently on the file server, and vers changes each time the file is modi‐
fied. The path is a long long (64 bits, vlong) and the vers is an
unsigned long (32 bits, ulong). 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)
0x04000000 non-backed-up files
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: DMDIR, DMAP‐
PEND, DMEXCL, and DMTMP for the first four; and DMREAD, DMWRITE, and
DMEXEC 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; muid is
the name of the user that last modified the file (setting mtime).
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 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 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 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 informa‐
tion about permissions and users(6) for users and groups). The length
can be changed by anyone with write permission, provided the operation
is implemented by the server. (See intro(5) for permission informa‐
tion, and users(6) for user and group information).
Special values in the fields of the Dir passed to wstat indicate that
the field is not intended to be changed by the call. The values are
the maximum unsigned integer of appropriate size for integral values
(usually ~0, but beware of conversions and size mismatches when compar‐
ing values) and the empty or nil string for string values. The routine
nulldir initializes all the elements of d to these ``don't care'' val‐
ues. Thus one may change the mode, for example, by using nulldir to
initialize a Dir, then setting the mode, and then doing wstat; it is
not necessary to use stat to retrieve the initial values first.
SOURCE
/sys/src/libc/9syscall
for the non-dir routines
/sys/src/libc/9sys
for the routines prefixed dir
SEE ALSOintro(2), fcall(2), dirread(2), stat(5)DIAGNOSTICS
The dir functions return a pointer to the data for a successful call,
or nil on error. The others return the number of bytes copied on suc‐
cess, or -1 on error. All set errstr.
If the buffer for stat or fstat is too short for the returned data, the
return value will be BIT16SZ (see fcall(2)) and the two bytes returned
will contain the initial count field of the returned data; retrying
with nedir equal to that value plus BIT16SZ (for the count itself)
should succeed.
STAT(2)
