tstat.3 - plan9port - [fork] Plan 9 from user space
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tstat.3 (6810B)
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1 .TH STAT 3
2 .SH NAME
3 stat, fstat, wstat, fwstat, dirstat, dirfstat, dirwstat, dirfwstat, nulldir \- get and put file status
4 .SH SYNOPSIS
5 .B #include <u.h>
6 .br
7 .B #include <libc.h>
8 .PP
9 .B
10 int stat(char *name, uchar *edir, int nedir)
11 .PP
12 .B
13 int fstat(int fd, uchar *edir, int nedir)
14 .PP
15 .B
16 int wstat(char *name, uchar *edir, int nedir)
17 .PP
18 .B
19 int fwstat(int fd, uchar *edir, int nedir)
20 .PP
21 .B
22 Dir* dirstat(char *name)
23 .PP
24 .B
25 Dir* dirfstat(int fd)
26 .PP
27 .B
28 int dirwstat(char *name, Dir *dir)
29 .PP
30 .B
31 int dirfwstat(int fd, Dir *dir)
32 .PP
33 .B
34 void nulldir(Dir *d)
35 .SH DESCRIPTION
36 Given a file's
37 .IR name ,
38 or an open file descriptor
39 .IR fd ,
40 these routines retrieve or modify file status information.
41 .IR Stat ,
42 .IR fstat ,
43 .IR wstat ,
44 and
45 .I fwstat
46 are the system calls; they deal with machine-independent
47 .IR "directory entries" .
48 Their format is defined by
49 .IR stat (9p).
50 .I Stat
51 and
52 .I fstat
53 retrieve information about
54 .I name
55 or
56 .I fd
57 into
58 .IR edir ,
59 a buffer of length
60 .IR nedir ,
61 defined in
62 .BR <libc.h> .
63 .I Wstat
64 and
65 .I fwstat
66 write information back, thus changing file attributes according to the contents of
67 .IR edir .
68 The data returned from the kernel includes its leading 16-bit length field
69 as described in
70 .IR intro (9p).
71 For symmetry, this field must also be present when passing data to the kernel in a call to
72 .I wstat
73 and
74 .IR fwstat ,
75 but its value is ignored.
76 .PP
77 .IR Dirstat ,
78 .IR dirfstat ,
79 .IR dirwstat ,
80 and
81 .I dirfwstat
82 are similar to their counterparts, except that they
83 operate on
84 .I Dir
85 structures:
86 .IP
87 .EX
88 .ta 6n +\w'ulong 'u +\w'mtime; 'u
89 typedef
90 struct Dir {
91 /* system-modified data */
92 uint type; /* server type */
93 uint dev; /* server subtype */
94 /* file data */
95 Qid qid; /* unique id from server */
96 ulong mode; /* permissions */
97 ulong atime; /* last read time */
98 ulong mtime; /* last write time */
99 vlong length; /* file length: see <u.h> */
100 char *name; /* last element of path */
101 char *uid; /* owner name */
102 char *gid; /* group name */
103 char *muid; /* last modifier name */
104 } Dir;
105 .EE
106 .PP
107 The returned structure is allocated by
108 .MR malloc (3) ;
109 freeing it also frees the associated strings.
110 .PP
111 This structure and
112 the
113 .B Qid
114 structure
115 are defined in
116 .BR <libc.h> .
117 If the file resides on permanent storage and is not a directory,
118 the length returned by
119 .I stat
120 is the number of bytes in the file.
121 For directories, the length returned is zero.
122 For files that are streams (e.g., pipes and network connections),
123 the length is the number of bytes that can be read without blocking.
124 .PP
125 Each file is the responsibility of some
126 .IR server :
127 it could be a file server, a kernel device, or a user process.
128 .B Type
129 identifies the server type, and
130 .B dev
131 says which of a group of servers of the same type is the one
132 responsible for this file.
133 .B Qid
134 is a structure containing
135 .B path
136 and
137 .B vers
138 fields:
139 .B path
140 is guaranteed to be
141 unique among all path names currently on the file server, and
142 .B vers
143 changes each time the file is modified.
144 The
145 .B path
146 is a
147 .B long
148 .B long
149 (64 bits,
150 .BR vlong )
151 and the
152 .B vers
153 is an
154 .B unsigned long
155 (32 bits,
156 .BR ulong ).
157 Thus, if two files have the same
158 .BR type ,
159 .BR dev ,
160 and
161 .B qid
162 they are the same file.
163 .PP
164 The bits in
165 .B mode
166 are defined by
167 .PP
168 .ta 6n +\w'\fL0x80000000 'u
169 .nf
170 \fL 0x80000000\fP directory
171 \fL 0x40000000\fP append only
172 \fL 0x20000000\fP exclusive use (locked)
173 \fL 0x00800000\fP Unix device file
174 \fL 0x02000000\fP symbolic link
175 \fL 0x00200000\fP named pipe
176 \fL 0x00100000\fP socket
177
178 \fL 0400\fP read permission by owner
179 \fL 0200\fP write permission by owner
180 \fL 0100\fP execute permission (search on directory) by owner
181 \fL 0070\fP read, write, execute (search) by group
182 \fL 0007\fP read, write, execute (search) by others
183 .fi
184 .PP
185 There are constants defined in
186 .B <libc.h>
187 for these bits:
188 .BR DMDIR ,
189 .BR DMAPPEND ,
190 and
191 .B DMEXCL
192 for the first three; and
193 .BR DMREAD ,
194 .BR DMWRITE ,
195 and
196 .B DMEXEC
197 for the read, write, and execute bits for others.
198 .PP
199 The two time fields are measured in seconds since the epoch
200 (Jan 1 00:00 1970 GMT).
201 .B Mtime
202 is the time of the last change of content.
203 Similarly,
204 .B atime
205 is set whenever the contents are accessed;
206 also, it is set whenever
207 .B mtime
208 is set.
209 .PP
210 .B Uid
211 and
212 .B gid
213 are the names of the owner and group of the file;
214 .B muid
215 is the name of the user that last modified the file (setting
216 .BR mtime ).
217 Groups are also users, but each server is free to associate
218 a list of users with any user name
219 .IR g ,
220 and that list is the
221 set of users in the group
222 .IR g .
223 When an initial attachment is made to a server,
224 the user string in the process group is communicated to the server.
225 Thus, the server knows, for any given file access, whether the accessing
226 process is the owner of, or in the group of, the file.
227 This selects which sets of three bits in
228 .B mode
229 is used to check permissions.
230 .PP
231 Only some of the fields may be changed with the
232 .I wstat
233 calls.
234 The
235 .B name
236 can be changed by anyone with write permission in the parent directory.
237 The
238 .B mode
239 and
240 .B mtime
241 can be changed by the owner or the group leader of the file's current
242 group.
243 The
244 .I gid
245 can be changed: by the owner if also a member of the new group; or
246 by the group leader of the file's current group
247 if also leader of the new group
248 (see
249 .IR intro (9p)
250 for more information about permissions, users, and groups).
251 The
252 .B length
253 can be changed by anyone with write permission, provided the operation
254 is implemented by the server.
255 (See
256 .IR intro (9p)
257 for permission, user, and group information).
258 .PP
259 Special values in the fields of the
260 .B Dir
261 passed to
262 .I wstat
263 indicate that the field is not intended to be changed by the call.
264 The values are the maximum unsigned integer of appropriate size
265 for integral values (usually
266 .BR ~0 ,
267 but beware of conversions and size mismatches
268 when comparing values) and the empty or nil string for string values.
269 The routine
270 .I nulldir
271 initializes all the elements of
272 .I d
273 to these ``don't care'' values.
274 Thus one may change the mode, for example, by using
275 .I nulldir
276 to initialize a
277 .BR Dir ,
278 then setting the mode, and then doing
279 .IR wstat ;
280 it is not necessary to use
281 .I stat
282 to retrieve the initial values first.
283 .SH SOURCE
284 .B \*9/src/lib9/dirstat.c
285 .SH SEE ALSO
286 .MR intro (3) ,
287 .MR fcall (3) ,
288 .MR dirread (3) ,
289 .IR stat (9p)
290 .SH DIAGNOSTICS
291 The
292 .I dir
293 functions return a pointer to the data for a successful call, or
294 .B nil
295 on error.
296 The others
297 return the number of bytes copied on success, or \-1 on error.
298 All set
299 .IR errstr .
300 .PP
301 If the buffer for
302 .I stat
303 or
304 .I fstat
305 is too short for the returned data, the return value will be
306 .B BIT16SZ
307 (see
308 .MR fcall (3) )
309 and the two bytes
310 returned will contain the initial count field of the
311 returned data;
312 retrying with
313 .B nedir
314 equal to
315 that value plus
316 .B BIT16SZ
317 (for the count itself) should succeed.