external/ibm-public/postfix/dist/src/global/dot_lockfile.c

   1 /*      $NetBSD$        */
   2
   3 /*++
   4 /* NAME
   5 /*      dot_lockfile 3
   6 /* SUMMARY
   7 /*      dotlock file management
   8 /* SYNOPSIS
   9 /*      #include <dot_lockfile.h>
  10 /*
  11 /*      int     dot_lockfile(path, why)
  12 /*      const char *path;
  13 /*      VSTRING *why;
  14 /*
  15 /*      void    dot_unlockfile(path)
  16 /*      const char *path;
  17 /* DESCRIPTION
  18 /*      dot_lockfile() constructs a lock file name by appending ".lock" to
  19 /*      \fIpath\fR and creates the named file exclusively. It tries several
  20 /*      times and attempts to break stale locks. A negative result value
  21 /*      means no lock file could be created.
  22 /*
  23 /*      dot_unlockfile() attempts to remove the lock file created by
  24 /*      dot_lockfile(). The operation always succeeds, and therefore
  25 /*      it preserves the errno value.
  26 /*
  27 /*      Arguments:
  28 /* .IP path
  29 /*      Name of the file to be locked or unlocked.
  30 /* .IP why
  31 /*      A null pointer, or storage for the reason why a lock file could
  32 /*      not be created.
  33 /* DIAGNOSTICS
  34 /*      dot_lockfile() returns 0 upon success. In case of failure, the
  35 /*      result is -1, and the errno variable is set appropriately:
  36 /*      EEXIST when a "fresh" lock file already exists; other values as
  37 /*      appropriate.
  38 /* CONFIGURATION PARAMETERS
  39 /*      deliver_lock_attempts, how many times to try to create a lock
  40 /*      deliver_lock_delay, how long to wait between attempts
  41 /*      stale_lock_time, when to break a stale lock
  42 /* LICENSE
  43 /* .ad
  44 /* .fi
  45 /*      The Secure Mailer license must be distributed with this software.
  46 /* AUTHOR(S)
  47 /*      Wietse Venema
  48 /*      IBM T.J. Watson Research
  49 /*      P.O. Box 704
  50 /*      Yorktown Heights, NY 10598, USA
  51 /*--*/
  52
  53 /* System library. */
  54
  55 #include "sys_defs.h"
  56 #include <sys/stat.h>
  57 #include <stdlib.h>
  58 #include <unistd.h>
  59 #include <fcntl.h>
  60 #include <errno.h>
  61 #include <time.h>
  62
  63 /* Utility library. */
  64
  65 #include <vstring.h>
  66 #include <stringops.h>
  67 #include <mymalloc.h>
  68 #include <iostuff.h>
  69
  70 /* Global library. */
  71
  72 #include "mail_params.h"
  73 #include "dot_lockfile.h"
  74
  75 /* Application-specific. */
  76
  77 #define MILLION 1000000
  78
  79 /* dot_lockfile - create user.lock file */
  80
  81 int     dot_lockfile(const char *path, VSTRING *why)
  82 {
  83     char   *lock_file;
  84     int     count;
  85     struct stat st;
  86     int     fd;
  87     int     status = -1;
  88
  89     lock_file = concatenate(path, ".lock", (char *) 0);
  90
  91     for (count = 1; /* void */ ; count++) {
  92
  93         /*
  94          * Attempt to create the lock. This code relies on O_EXCL | O_CREAT
  95          * to not follow symlinks. With NFS file systems this operation can
  96          * at the same time succeed and fail with errno of EEXIST.
  97          */
  98         if ((fd = open(lock_file, O_WRONLY | O_EXCL | O_CREAT, 0)) >= 0) {
  99             close(fd);
 100             status = 0;
 101             break;
 102         }
 103         if (count >= var_flock_tries)
 104             break;
 105
 106         /*
 107          * We can deal only with "file exists" errors. Any other error means
 108          * we better give up trying.
 109          */
 110         if (errno != EEXIST)
 111             break;
 112
 113         /*
 114          * Break the lock when it is too old. Give up when we are unable to
 115          * remove a stale lock.
 116          */
 117         if (stat(lock_file, &st) == 0)
 118             if (time((time_t *) 0) > st.st_ctime + var_flock_stale)
 119                 if (unlink(lock_file) < 0)
 120                     if (errno != ENOENT)
 121                         break;
 122
 123         rand_sleep(var_flock_delay * MILLION, var_flock_delay * MILLION / 2);
 124     }
 125     if (status && why)
 126         vstring_sprintf(why, "unable to create lock file %s: %m", lock_file);
 127
 128     myfree(lock_file);
 129     return (status);
 130 }
 131
 132 /* dot_unlockfile - remove .lock file */
 133
 134 void    dot_unlockfile(const char *path)
 135 {
 136     char   *lock_file;
 137     int     saved_errno = errno;
 138
 139     lock_file = concatenate(path, ".lock", (char *) 0);
 140     (void) unlink(lock_file);
 141     myfree(lock_file);
 142     errno = saved_errno;
 143 }
 144
 145 #ifdef TEST
 146
 147  /*
 148   * Test program for setting a .lock file.
 149   *
 150   * Usage: dot_lockfile filename
 151   *
 152   * Creates filename.lock and removes it.
 153   */
 154 #include <msg.h>
 155 #include <vstream.h>
 156 #include <msg_vstream.h>
 157 #include <mail_conf.h>
 158
 159 int     main(int argc, char **argv)
 160 {
 161     VSTRING *why = vstring_alloc(100);
 162
 163     msg_vstream_init(argv[0], VSTREAM_ERR);
 164     if (argc != 2)
 165         msg_fatal("usage: %s file-to-be-locked", argv[0]);
 166     mail_conf_read();
 167     if (dot_lockfile(argv[1], why) < 0)
 168         msg_fatal("%s", vstring_str(why));
 169     dot_unlockfile(argv[1]);
 170     vstring_free(why);
 171     return (0);
 172 }
 173
 174 #endif