src/fcatomic.c

   1 /*
   2  * fontconfig/src/fcatomic.c
   3  *
   4  * Copyright © 2002 Keith Packard
   5  *
   6  * Permission to use, copy, modify, distribute, and sell this software and its
   7  * documentation for any purpose is hereby granted without fee, provided that
   8  * the above copyright notice appear in all copies and that both that
   9  * copyright notice and this permission notice appear in supporting
  10  * documentation, and that the name of the author(s) not be used in
  11  * advertising or publicity pertaining to distribution of the software without
  12  * specific, written prior permission.  The authors make no
  13  * representations about the suitability of this software for any purpose.  It
  14  * is provided "as is" without express or implied warranty.
  15  *
  16  * THE AUTHOR(S) DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
  17  * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
  18  * EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY SPECIAL, INDIRECT OR
  19  * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
  20  * DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
  21  * TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
  22  * PERFORMANCE OF THIS SOFTWARE.
  23  */
  24
  25 /*
  26  * fcatomic.c
  27  *
  28  * Lock cache and configuration files for atomic update
  29  *
  30  * Uses only regular filesystem calls so it should
  31  * work even in the absense of functioning file locking
  32  *
  33  * On Unix, four files are used:
  34  *      file        - the data file accessed by other apps.
  35  *      new         - a new version of the data file while it's being written
  36  *      lck         - the lock file
  37  *      tmp         - a temporary file made unique with mkstemp
  38  *
  39  *  Here's how it works:
  40  *      Create 'tmp' and store our PID in it
  41  *      Attempt to link it to 'lck'
  42  *      Unlink 'tmp'
  43  *      If the link succeeded, the lock is held
  44  *
  45  * On Windows, where there are no links, no tmp file is used, and lck
  46  * is a directory that's mkdir'ed. If the mkdir succeeds, the lock is
  47  * held.
  48  */
  49
  50 #include "fcint.h"
  51 #include <sys/types.h>
  52 #include <sys/stat.h>
  53 #include <fcntl.h>
  54 #include <unistd.h>
  55 #include <stdlib.h>
  56 #include <time.h>
  57
  58 #ifdef _WIN32
  59 #define mkdir(path,mode) _mkdir(path)
  60 #endif
  61
  62 #define NEW_NAME        ".NEW"
  63 #define LCK_NAME        ".LCK"
  64 #define TMP_NAME        ".TMP-XXXXXX"
  65
  66 FcAtomic *
  67 FcAtomicCreate (const FcChar8   *file)
  68 {
  69     int     file_len = strlen ((char *) file);
  70     int     new_len = file_len + sizeof (NEW_NAME);
  71     int     lck_len = file_len + sizeof (LCK_NAME);
  72     int     tmp_len = file_len + sizeof (TMP_NAME);
  73     int     total_len = (sizeof (FcAtomic) +
  74                          file_len + 1 +
  75                          new_len + 1 +
  76                          lck_len + 1 +
  77                          tmp_len + 1);
  78     FcAtomic    *atomic = malloc (total_len);
  79     if (!atomic)
  80         return 0;
  81     FcMemAlloc (FC_MEM_ATOMIC, total_len);
  82
  83     atomic->file = (FcChar8 *) (atomic + 1);
  84     strcpy ((char *) atomic->file, (char *) file);
  85
  86     atomic->new = atomic->file + file_len + 1;
  87     strcpy ((char *) atomic->new, (char *) file);
  88     strcat ((char *) atomic->new, NEW_NAME);
  89
  90     atomic->lck = atomic->new + new_len + 1;
  91     strcpy ((char *) atomic->lck, (char *) file);
  92     strcat ((char *) atomic->lck, LCK_NAME);
  93
  94     atomic->tmp = atomic->lck + lck_len + 1;
  95
  96     return atomic;
  97 }
  98
  99 FcBool
 100 FcAtomicLock (FcAtomic *atomic)
 101 {
 102     int         fd = -1;
 103     FILE        *f = 0;
 104     int         ret;
 105     struct stat lck_stat;
 106
 107 #ifdef HAVE_LINK
 108     strcpy ((char *) atomic->tmp, (char *) atomic->file);
 109     strcat ((char *) atomic->tmp, TMP_NAME);
 110     fd = mkstemp ((char *) atomic->tmp);
 111     if (fd < 0)
 112         return FcFalse;
 113     f = fdopen (fd, "w");
 114     if (!f)
 115     {
 116         close (fd);
 117         unlink ((char *) atomic->tmp);
 118         return FcFalse;
 119     }
 120     ret = fprintf (f, "%ld\n", (long)getpid());
 121     if (ret <= 0)
 122     {
 123         fclose (f);
 124         unlink ((char *) atomic->tmp);
 125         return FcFalse;
 126     }
 127     if (fclose (f) == EOF)
 128     {
 129         unlink ((char *) atomic->tmp);
 130         return FcFalse;
 131     }
 132     ret = link ((char *) atomic->tmp, (char *) atomic->lck);
 133     (void) unlink ((char *) atomic->tmp);
 134 #else
 135     ret = mkdir ((char *) atomic->lck, 0600);
 136 #endif
 137     if (ret < 0)
 138     {
 139         /*
 140          * If the file is around and old (> 10 minutes),
 141          * assume the lock is stale.  This assumes that any
 142          * machines sharing the same filesystem will have clocks
 143          * reasonably close to each other.
 144          */
 145         if (FcStat (atomic->lck, &lck_stat) >= 0)
 146         {
 147             time_t  now = time (0);
 148             if ((long int) (now - lck_stat.st_mtime) > 10 * 60)
 149             {
 150 #ifdef HAVE_LINK
 151                 if (unlink ((char *) atomic->lck) == 0)
 152                     return FcAtomicLock (atomic);
 153 #else
 154                 if (rmdir ((char *) atomic->lck) == 0)
 155                     return FcAtomicLock (atomic);
 156 #endif
 157             }
 158         }
 159         return FcFalse;
 160     }
 161     (void) unlink ((char *) atomic->new);
 162     return FcTrue;
 163 }
 164
 165 FcChar8 *
 166 FcAtomicNewFile (FcAtomic *atomic)
 167 {
 168     return atomic->new;
 169 }
 170
 171 FcChar8 *
 172 FcAtomicOrigFile (FcAtomic *atomic)
 173 {
 174     return atomic->file;
 175 }
 176
 177 FcBool
 178 FcAtomicReplaceOrig (FcAtomic *atomic)
 179 {
 180 #ifdef _WIN32
 181     unlink (atomic->file);
 182 #endif
 183     if (rename ((char *) atomic->new, (char *) atomic->file) < 0)
 184         return FcFalse;
 185     return FcTrue;
 186 }
 187
 188 void
 189 FcAtomicDeleteNew (FcAtomic *atomic)
 190 {
 191     unlink ((char *) atomic->new);
 192 }
 193
 194 void
 195 FcAtomicUnlock (FcAtomic *atomic)
 196 {
 197 #ifdef HAVE_LINK
 198     unlink ((char *) atomic->lck);
 199 #else
 200     rmdir ((char *) atomic->lck);
 201 #endif
 202 }
 203
 204 void
 205 FcAtomicDestroy (FcAtomic *atomic)
 206 {
 207     FcMemFree (FC_MEM_ATOMIC, sizeof (FcAtomic) +
 208                strlen ((char *) atomic->file) * 4 + 4 +
 209                sizeof (NEW_NAME) + sizeof (LCK_NAME) +
 210                sizeof (TMP_NAME));
 211
 212     free (atomic);
 213 }
 214 #define __fcatomic__
 215 #include "fcaliastail.h"
 216 #undef __fcatomic__