src/fcatomic.c

   1 /*
   2  * $XFree86: $
   3  *
   4  * Copyright © 2002 Keith Packard, member of The XFree86 Project, Inc.
   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 Keith Packard not be used in
  11  * advertising or publicity pertaining to distribution of the software without
  12  * specific, written prior permission.  Keith Packard makes 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  * KEITH PACKARD DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
  17  * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
  18  * EVENT SHALL KEITH PACKARD 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  *  Four files:
  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
  46 #include "fcint.h"
  47 #include <sys/types.h>
  48 #include <sys/stat.h>
  49 #include <fcntl.h>
  50 #include <unistd.h>
  51 #include <stdlib.h>
  52 #include <time.h>
  53
  54 #define NEW_NAME        ".NEW"
  55 #define LCK_NAME        ".LCK"
  56 #define TMP_NAME        ".TMP-XXXXXX"
  57
  58 FcAtomic *
  59 FcAtomicCreate (const FcChar8   *file)
  60 {
  61     int     file_len = strlen ((char *) file);
  62     int     new_len = file_len + sizeof (NEW_NAME);
  63     int     lck_len = file_len + sizeof (LCK_NAME);
  64     int     tmp_len = file_len + sizeof (TMP_NAME);
  65     int     total_len = (sizeof (FcAtomic) +
  66                          file_len + 1 +
  67                          new_len + 1 +
  68                          lck_len + 1 +
  69                          tmp_len + 1);
  70     FcAtomic    *atomic = malloc (total_len);
  71     if (!atomic)
  72         return 0;
  73
  74     atomic->file = (FcChar8 *) (atomic + 1);
  75     strcpy ((char *) atomic->file, (char *) file);
  76
  77     atomic->new = atomic->file + file_len + 1;
  78     strcpy ((char *) atomic->new, (char *) file);
  79     strcat ((char *) atomic->new, NEW_NAME);
  80
  81     atomic->lck = atomic->new + new_len + 1;
  82     strcpy ((char *) atomic->lck, (char *) file);
  83     strcat ((char *) atomic->lck, LCK_NAME);
  84
  85     atomic->tmp = atomic->lck + lck_len + 1;
  86
  87     return atomic;
  88 }
  89
  90 FcBool
  91 FcAtomicLock (FcAtomic *atomic)
  92 {
  93     int         fd = -1;
  94     FILE        *f = 0;
  95     int         ret;
  96     struct stat lck_stat;
  97
  98     strcpy ((char *) atomic->tmp, (char *) atomic->file);
  99     strcat ((char *) atomic->tmp, TMP_NAME);
 100     fd = mkstemp ((char *) atomic->tmp);
 101     if (fd < 0)
 102         return FcFalse;
 103     f = fdopen (fd, "w");
 104     if (!f)
 105     {
 106         close (fd);
 107         unlink ((char *) atomic->tmp);
 108         return FcFalse;
 109     }
 110     ret = fprintf (f, "%d\n", getpid());
 111     if (ret <= 0)
 112     {
 113         fclose (f);
 114         unlink ((char *) atomic->tmp);
 115         return FcFalse;
 116     }
 117     if (fclose (f) == EOF)
 118     {
 119         unlink ((char *) atomic->tmp);
 120         return FcFalse;
 121     }
 122     ret = link ((char *) atomic->tmp, (char *) atomic->lck);
 123     (void) unlink ((char *) atomic->tmp);
 124     if (ret < 0)
 125     {
 126         /*
 127          * If the file is around and old (> 10 minutes),
 128          * assume the lock is stale.  This assumes that any
 129          * machines sharing the same filesystem will have clocks
 130          * reasonably close to each other.
 131          */
 132         if (stat ((char *) atomic->lck, &lck_stat) >= 0)
 133         {
 134             time_t  now = time (0);
 135             if ((long int) (now - lck_stat.st_mtime) > 10 * 60)
 136             {
 137                 if (unlink ((char *) atomic->lck) == 0)
 138                     return FcAtomicLock (atomic);
 139             }
 140         }
 141         return FcFalse;
 142     }
 143     (void) unlink ((char *) atomic->new);
 144     return FcTrue;
 145 }
 146
 147 FcChar8 *
 148 FcAtomicNewFile (FcAtomic *atomic)
 149 {
 150     return atomic->new;
 151 }
 152
 153 FcChar8 *
 154 FcAtomicOrigFile (FcAtomic *atomic)
 155 {
 156     return atomic->file;
 157 }
 158
 159 FcBool
 160 FcAtomicReplaceOrig (FcAtomic *atomic)
 161 {
 162     if (rename ((char *) atomic->new, (char *) atomic->file) < 0)
 163         return FcFalse;
 164     return FcTrue;
 165 }
 166
 167 void
 168 FcAtomicDeleteNew (FcAtomic *atomic)
 169 {
 170     unlink ((char *) atomic->new);
 171 }
 172
 173 void
 174 FcAtomicUnlock (FcAtomic *atomic)
 175 {
 176     unlink ((char *) atomic->lck);
 177 }
 178
 179 void
 180 FcAtomicDestroy (FcAtomic *atomic)
 181 {
 182     free (atomic);
 183 }