Improve documentation of 'window-use-time'
[emacs.git] / lib / tempname.c
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1 /* tempname.c - generate the name of a temporary file.
3 Copyright (C) 1991-2003, 2005-2007, 2009-2015 Free Software Foundation, Inc.
5 This program is free software: you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation; either version 3 of the License, or
8 (at your option) any later version.
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>. */
18 /* Extracted from glibc sysdeps/posix/tempname.c. See also tmpdir.c. */
20 #if !_LIBC
21 # include <config.h>
22 # include "tempname.h"
23 #endif
25 #include <sys/types.h>
26 #include <assert.h>
28 #include <errno.h>
29 #ifndef __set_errno
30 # define __set_errno(Val) errno = (Val)
31 #endif
33 #include <stdio.h>
34 #ifndef P_tmpdir
35 # define P_tmpdir "/tmp"
36 #endif
37 #ifndef TMP_MAX
38 # define TMP_MAX 238328
39 #endif
40 #ifndef __GT_FILE
41 # define __GT_FILE 0
42 # define __GT_DIR 1
43 # define __GT_NOCREATE 2
44 #endif
45 #if !_LIBC && (GT_FILE != __GT_FILE || GT_DIR != __GT_DIR \
46 || GT_NOCREATE != __GT_NOCREATE)
47 # error report this to bug-gnulib@gnu.org
48 #endif
50 #include <stddef.h>
51 #include <stdlib.h>
52 #include <string.h>
54 #include <fcntl.h>
55 #include <sys/time.h>
56 #include <stdint.h>
57 #include <unistd.h>
59 #include <sys/stat.h>
61 #if _LIBC
62 # define struct_stat64 struct stat64
63 #else
64 # define struct_stat64 struct stat
65 # define __try_tempname try_tempname
66 # define __gen_tempname gen_tempname
67 # define __getpid getpid
68 # define __gettimeofday gettimeofday
69 # define __mkdir mkdir
70 # define __open open
71 # define __lxstat64(version, file, buf) lstat (file, buf)
72 # define __secure_getenv secure_getenv
73 #endif
75 #ifdef _LIBC
76 # include <hp-timing.h>
77 # if HP_TIMING_AVAIL
78 # define RANDOM_BITS(Var) \
79 if (__builtin_expect (value == UINT64_C (0), 0)) \
80 { \
81 /* If this is the first time this function is used initialize \
82 the variable we accumulate the value in to some somewhat \
83 random value. If we'd not do this programs at startup time \
84 might have a reduced set of possible names, at least on slow \
85 machines. */ \
86 struct timeval tv; \
87 __gettimeofday (&tv, NULL); \
88 value = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec; \
89 } \
90 HP_TIMING_NOW (Var)
91 # endif
92 #endif
94 /* Use the widest available unsigned type if uint64_t is not
95 available. The algorithm below extracts a number less than 62**6
96 (approximately 2**35.725) from uint64_t, so ancient hosts where
97 uintmax_t is only 32 bits lose about 3.725 bits of randomness,
98 which is better than not having mkstemp at all. */
99 #if !defined UINT64_MAX && !defined uint64_t
100 # define uint64_t uintmax_t
101 #endif
103 #if _LIBC
104 /* Return nonzero if DIR is an existent directory. */
105 static int
106 direxists (const char *dir)
108 struct_stat64 buf;
109 return __xstat64 (_STAT_VER, dir, &buf) == 0 && S_ISDIR (buf.st_mode);
112 /* Path search algorithm, for tmpnam, tmpfile, etc. If DIR is
113 non-null and exists, uses it; otherwise uses the first of $TMPDIR,
114 P_tmpdir, /tmp that exists. Copies into TMPL a template suitable
115 for use with mk[s]temp. Will fail (-1) if DIR is non-null and
116 doesn't exist, none of the searched dirs exists, or there's not
117 enough space in TMPL. */
119 __path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx,
120 int try_tmpdir)
122 const char *d;
123 size_t dlen, plen;
125 if (!pfx || !pfx[0])
127 pfx = "file";
128 plen = 4;
130 else
132 plen = strlen (pfx);
133 if (plen > 5)
134 plen = 5;
137 if (try_tmpdir)
139 d = __secure_getenv ("TMPDIR");
140 if (d != NULL && direxists (d))
141 dir = d;
142 else if (dir != NULL && direxists (dir))
143 /* nothing */ ;
144 else
145 dir = NULL;
147 if (dir == NULL)
149 if (direxists (P_tmpdir))
150 dir = P_tmpdir;
151 else if (strcmp (P_tmpdir, "/tmp") != 0 && direxists ("/tmp"))
152 dir = "/tmp";
153 else
155 __set_errno (ENOENT);
156 return -1;
160 dlen = strlen (dir);
161 while (dlen > 1 && dir[dlen - 1] == '/')
162 dlen--; /* remove trailing slashes */
164 /* check we have room for "${dir}/${pfx}XXXXXX\0" */
165 if (tmpl_len < dlen + 1 + plen + 6 + 1)
167 __set_errno (EINVAL);
168 return -1;
171 sprintf (tmpl, "%.*s/%.*sXXXXXX", (int) dlen, dir, (int) plen, pfx);
172 return 0;
174 #endif /* _LIBC */
176 /* These are the characters used in temporary file names. */
177 static const char letters[] =
178 "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
181 __try_tempname (char *tmpl, int suffixlen, void *args,
182 int (*tryfunc) (char *, void *))
184 int len;
185 char *XXXXXX;
186 static uint64_t value;
187 uint64_t random_time_bits;
188 unsigned int count;
189 int fd = -1;
190 int save_errno = errno;
192 /* A lower bound on the number of temporary files to attempt to
193 generate. The maximum total number of temporary file names that
194 can exist for a given template is 62**6. It should never be
195 necessary to try all of these combinations. Instead if a reasonable
196 number of names is tried (we define reasonable as 62**3) fail to
197 give the system administrator the chance to remove the problems. */
198 #define ATTEMPTS_MIN (62 * 62 * 62)
200 /* The number of times to attempt to generate a temporary file. To
201 conform to POSIX, this must be no smaller than TMP_MAX. */
202 #if ATTEMPTS_MIN < TMP_MAX
203 unsigned int attempts = TMP_MAX;
204 #else
205 unsigned int attempts = ATTEMPTS_MIN;
206 #endif
208 len = strlen (tmpl);
209 if (len < 6 + suffixlen || memcmp (&tmpl[len - 6 - suffixlen], "XXXXXX", 6))
211 __set_errno (EINVAL);
212 return -1;
215 /* This is where the Xs start. */
216 XXXXXX = &tmpl[len - 6 - suffixlen];
218 /* Get some more or less random data. */
219 #ifdef RANDOM_BITS
220 RANDOM_BITS (random_time_bits);
221 #else
223 struct timeval tv;
224 __gettimeofday (&tv, NULL);
225 random_time_bits = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;
227 #endif
228 value += random_time_bits ^ __getpid ();
230 for (count = 0; count < attempts; value += 7777, ++count)
232 uint64_t v = value;
234 /* Fill in the random bits. */
235 XXXXXX[0] = letters[v % 62];
236 v /= 62;
237 XXXXXX[1] = letters[v % 62];
238 v /= 62;
239 XXXXXX[2] = letters[v % 62];
240 v /= 62;
241 XXXXXX[3] = letters[v % 62];
242 v /= 62;
243 XXXXXX[4] = letters[v % 62];
244 v /= 62;
245 XXXXXX[5] = letters[v % 62];
247 fd = tryfunc (tmpl, args);
248 if (fd >= 0)
250 __set_errno (save_errno);
251 return fd;
253 else if (errno != EEXIST)
254 return -1;
257 /* We got out of the loop because we ran out of combinations to try. */
258 __set_errno (EEXIST);
259 return -1;
262 static int
263 try_file (char *tmpl, void *flags)
265 int *openflags = flags;
266 return __open (tmpl,
267 (*openflags & ~O_ACCMODE)
268 | O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
271 static int
272 try_dir (char *tmpl, void *flags _GL_UNUSED)
274 return __mkdir (tmpl, S_IRUSR | S_IWUSR | S_IXUSR);
277 static int
278 try_nocreate (char *tmpl, void *flags _GL_UNUSED)
280 struct_stat64 st;
282 if (__lxstat64 (_STAT_VER, tmpl, &st) == 0)
283 __set_errno (EEXIST);
284 return errno == ENOENT ? 0 : -1;
287 /* Generate a temporary file name based on TMPL. TMPL must match the
288 rules for mk[s]temp (i.e. end in "XXXXXX", possibly with a suffix).
289 The name constructed does not exist at the time of the call to
290 __gen_tempname. TMPL is overwritten with the result.
292 KIND may be one of:
293 __GT_NOCREATE: simply verify that the name does not exist
294 at the time of the call.
295 __GT_FILE: create the file using open(O_CREAT|O_EXCL)
296 and return a read-write fd. The file is mode 0600.
297 __GT_DIR: create a directory, which will be mode 0700.
299 We use a clever algorithm to get hard-to-predict names. */
301 __gen_tempname (char *tmpl, int suffixlen, int flags, int kind)
303 int (*tryfunc) (char *, void *);
305 switch (kind)
307 case __GT_FILE:
308 tryfunc = try_file;
309 break;
311 case __GT_DIR:
312 tryfunc = try_dir;
313 break;
315 case __GT_NOCREATE:
316 tryfunc = try_nocreate;
317 break;
319 default:
320 assert (! "invalid KIND in __gen_tempname");
321 abort ();
323 return __try_tempname (tmpl, suffixlen, &flags, tryfunc);