external/gpl2/xcvs/dist/lib/tempname.c

   1 /* tempname.c - generate the name of a temporary file.
   2
   3    Copyright (C) 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
   4    2000, 2001, 2002, 2003, 2005 Free Software Foundation, Inc.
   5
   6    This program is free software; you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 2, or (at your option)
   9    any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License along
  17    with this program; if not, write to the Free Software Foundation,
  18    Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
  19
  20 #ifdef HAVE_CONFIG_H
  21 # include <config.h>
  22 #endif
  23
  24 #include <sys/types.h>
  25 #include <assert.h>
  26
  27 #include <errno.h>
  28 #ifndef __set_errno
  29 # define __set_errno(Val) errno = (Val)
  30 #endif
  31
  32 #include <stdio.h>
  33 #ifndef P_tmpdir
  34 # define P_tmpdir "/tmp"
  35 #endif
  36 #ifndef TMP_MAX
  37 # define TMP_MAX 238328
  38 #endif
  39 #ifndef __GT_FILE
  40 # define __GT_FILE      0
  41 # define __GT_BIGFILE   1
  42 # define __GT_DIR       2
  43 # define __GT_NOCREATE  3
  44 #endif
  45
  46 #include <stddef.h>
  47 #include <stdlib.h>
  48 #include <string.h>
  49
  50 #include <fcntl.h>
  51
  52 #if HAVE_SYS_TIME_H || _LIBC
  53 # include <sys/time.h>
  54 #endif
  55
  56 #if HAVE_STDINT_H || _LIBC
  57 # include <stdint.h>
  58 #endif
  59 #if HAVE_INTTYPES_H
  60 # include <inttypes.h>
  61 #endif
  62
  63 #if HAVE_UNISTD_H || _LIBC
  64 # include <unistd.h>
  65 #endif
  66
  67 #include <sys/stat.h>
  68
  69 #if _LIBC
  70 # define struct_stat64 struct stat64
  71 #else
  72 # include "stat-macros.h"
  73 # define struct_stat64 struct stat
  74 # define __getpid getpid
  75 # define __gettimeofday gettimeofday
  76 # define __mkdir mkdir
  77 # define __open open
  78 # define __open64 open
  79 # define __lxstat64(version, file, buf) lstat (file, buf)
  80 # define __xstat64(version, file, buf) stat (file, buf)
  81 #endif
  82
  83 #if ! (HAVE___SECURE_GETENV || _LIBC)
  84 # define __secure_getenv getenv
  85 #endif
  86
  87 #ifdef _LIBC
  88 # include <hp-timing.h>
  89 # if HP_TIMING_AVAIL
  90 #  define RANDOM_BITS(Var) \
  91   if (__builtin_expect (value == UINT64_C (0), 0))                            \
  92     {                                                                         \
  93       /* If this is the first time this function is used initialize           \
  94          the variable we accumulate the value in to some somewhat             \
  95          random value.  If we'd not do this programs at startup time          \
  96          might have a reduced set of possible names, at least on slow         \
  97          machines.  */                                                        \
  98       struct timeval tv;                                                      \
  99       __gettimeofday (&tv, NULL);                                             \
 100       value = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;                      \
 101     }                                                                         \
 102   HP_TIMING_NOW (Var)
 103 # endif
 104 #endif
 105
 106 /* Use the widest available unsigned type if uint64_t is not
 107    available.  The algorithm below extracts a number less than 62**6
 108    (approximately 2**35.725) from uint64_t, so ancient hosts where
 109    uintmax_t is only 32 bits lose about 3.725 bits of randomness,
 110    which is better than not having mkstemp at all.  */
 111 #if !defined UINT64_MAX && !defined uint64_t
 112 # define uint64_t uintmax_t
 113 #endif
 114
 115 /* Return nonzero if DIR is an existent directory.  */
 116 static int
 117 direxists (const char *dir)
 118 {
 119   struct_stat64 buf;
 120   return __xstat64 (_STAT_VER, dir, &buf) == 0 && S_ISDIR (buf.st_mode);
 121 }
 122
 123 /* Path search algorithm, for tmpnam, tmpfile, etc.  If DIR is
 124    non-null and exists, uses it; otherwise uses the first of $TMPDIR,
 125    P_tmpdir, /tmp that exists.  Copies into TMPL a template suitable
 126    for use with mk[s]temp.  Will fail (-1) if DIR is non-null and
 127    doesn't exist, none of the searched dirs exists, or there's not
 128    enough space in TMPL. */
 129 int
 130 __path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx,
 131                int try_tmpdir)
 132 {
 133   const char *d;
 134   size_t dlen, plen;
 135
 136   if (!pfx || !pfx[0])
 137     {
 138       pfx = "file";
 139       plen = 4;
 140     }
 141   else
 142     {
 143       plen = strlen (pfx);
 144       if (plen > 5)
 145         plen = 5;
 146     }
 147
 148   if (try_tmpdir)
 149     {
 150       d = __secure_getenv ("TMPDIR");
 151       if (d != NULL && direxists (d))
 152         dir = d;
 153       else if (dir != NULL && direxists (dir))
 154         /* nothing */ ;
 155       else
 156         dir = NULL;
 157     }
 158   if (dir == NULL)
 159     {
 160       if (direxists (P_tmpdir))
 161         dir = P_tmpdir;
 162       else if (strcmp (P_tmpdir, "/tmp") != 0 && direxists ("/tmp"))
 163         dir = "/tmp";
 164       else
 165         {
 166           __set_errno (ENOENT);
 167           return -1;
 168         }
 169     }
 170
 171   dlen = strlen (dir);
 172   while (dlen > 1 && dir[dlen - 1] == '/')
 173     dlen--;                     /* remove trailing slashes */
 174
 175   /* check we have room for "${dir}/${pfx}XXXXXX\0" */
 176   if (tmpl_len < dlen + 1 + plen + 6 + 1)
 177     {
 178       __set_errno (EINVAL);
 179       return -1;
 180     }
 181
 182   sprintf (tmpl, "%.*s/%.*sXXXXXX", (int) dlen, dir, (int) plen, pfx);
 183   return 0;
 184 }
 185
 186 /* These are the characters used in temporary file names.  */
 187 static const char letters[] =
 188 "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
 189
 190 /* Generate a temporary file name based on TMPL.  TMPL must match the
 191    rules for mk[s]temp (i.e. end in "XXXXXX").  The name constructed
 192    does not exist at the time of the call to __gen_tempname.  TMPL is
 193    overwritten with the result.
 194
 195    KIND may be one of:
 196    __GT_NOCREATE:       simply verify that the name does not exist
 197                         at the time of the call.
 198    __GT_FILE:           create the file using open(O_CREAT|O_EXCL)
 199                         and return a read-write fd.  The file is mode 0600.
 200    __GT_BIGFILE:        same as __GT_FILE but use open64().
 201    __GT_DIR:            create a directory, which will be mode 0700.
 202
 203    We use a clever algorithm to get hard-to-predict names. */
 204 int
 205 __gen_tempname (char *tmpl, int kind)
 206 {
 207   int len;
 208   char *XXXXXX;
 209   static uint64_t value;
 210   uint64_t random_time_bits;
 211   unsigned int count;
 212   int fd = -1;
 213   int save_errno = errno;
 214   struct_stat64 st;
 215
 216   /* A lower bound on the number of temporary files to attempt to
 217      generate.  The maximum total number of temporary file names that
 218      can exist for a given template is 62**6.  It should never be
 219      necessary to try all these combinations.  Instead if a reasonable
 220      number of names is tried (we define reasonable as 62**3) fail to
 221      give the system administrator the chance to remove the problems.  */
 222   unsigned int attempts_min = 62 * 62 * 62;
 223
 224   /* The number of times to attempt to generate a temporary file.  To
 225      conform to POSIX, this must be no smaller than TMP_MAX.  */
 226   unsigned int attempts = attempts_min < TMP_MAX ? TMP_MAX : attempts_min;
 227
 228   len = strlen (tmpl);
 229   if (len < 6 || strcmp (&tmpl[len - 6], "XXXXXX"))
 230     {
 231       __set_errno (EINVAL);
 232       return -1;
 233     }
 234
 235   /* This is where the Xs start.  */
 236   XXXXXX = &tmpl[len - 6];
 237
 238   /* Get some more or less random data.  */
 239 #ifdef RANDOM_BITS
 240   RANDOM_BITS (random_time_bits);
 241 #else
 242 # if HAVE_GETTIMEOFDAY || _LIBC
 243   {
 244     struct timeval tv;
 245     __gettimeofday (&tv, NULL);
 246     random_time_bits = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;
 247   }
 248 # else
 249   random_time_bits = time (NULL);
 250 # endif
 251 #endif
 252   value += random_time_bits ^ __getpid ();
 253
 254   for (count = 0; count < attempts; value += 7777, ++count)
 255     {
 256       uint64_t v = value;
 257
 258       /* Fill in the random bits.  */
 259       XXXXXX[0] = letters[v % 62];
 260       v /= 62;
 261       XXXXXX[1] = letters[v % 62];
 262       v /= 62;
 263       XXXXXX[2] = letters[v % 62];
 264       v /= 62;
 265       XXXXXX[3] = letters[v % 62];
 266       v /= 62;
 267       XXXXXX[4] = letters[v % 62];
 268       v /= 62;
 269       XXXXXX[5] = letters[v % 62];
 270
 271       switch (kind)
 272         {
 273         case __GT_FILE:
 274           fd = __open (tmpl, O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
 275           break;
 276
 277         case __GT_BIGFILE:
 278           fd = __open64 (tmpl, O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
 279           break;
 280
 281         case __GT_DIR:
 282           fd = __mkdir (tmpl, S_IRUSR | S_IWUSR | S_IXUSR);
 283           break;
 284
 285         case __GT_NOCREATE:
 286           /* This case is backward from the other three.  __gen_tempname
 287              succeeds if __xstat fails because the name does not exist.
 288              Note the continue to bypass the common logic at the bottom
 289              of the loop.  */
 290           if (__lxstat64 (_STAT_VER, tmpl, &st) < 0)
 291             {
 292               if (errno == ENOENT)
 293                 {
 294                   __set_errno (save_errno);
 295                   return 0;
 296                 }
 297               else
 298                 /* Give up now. */
 299                 return -1;
 300             }
 301           continue;
 302
 303         default:
 304           assert (! "invalid KIND in __gen_tempname");
 305         }
 306
 307       if (fd >= 0)
 308         {
 309           __set_errno (save_errno);
 310           return fd;
 311         }
 312       else if (errno != EEXIST)
 313         return -1;
 314     }
 315
 316   /* We got out of the loop because we ran out of combinations to try.  */
 317   __set_errno (EEXIST);
 318   return -1;
 319 }