external/ibm-public/postfix/dist/src/util/open_lock.c

   1 /*      $NetBSD$        */
   2
   3 /*++
   4 /* NAME
   5 /*      open_lock 3
   6 /* SUMMARY
   7 /*      open or create file and lock it for exclusive access
   8 /* SYNOPSIS
   9 /*      #include <open_lock.h>
  10 /*
  11 /*      VSTREAM *open_lock(path, flags, mode, why)
  12 /*      const char *path;
  13 /*      int     flags;
  14 /*      mode_t  mode;
  15 /*      VSTRING *why;
  16 /* DESCRIPTION
  17 /*      This module opens or creates the named file and attempts to
  18 /*      acquire an exclusive lock.  The lock is lost when the last
  19 /*      process closes the file.
  20 /*
  21 /*      Arguments:
  22 /* .IP "path, flags, mode"
  23 /*      These are passed on to safe_open().
  24 /* .IP why
  25 /*      storage for diagnostics.
  26 /* SEE ALSO
  27 /*      safe_open(3) carefully open or create file
  28 /*      myflock(3) get exclusive lock on file
  29 /* DIAGNOSTICS
  30 /*      In case of problems the result is a null pointer and a problem
  31 /*      description is returned via the global \fIerrno\fR variable.
  32 /* LICENSE
  33 /* .ad
  34 /* .fi
  35 /*      The Secure Mailer license must be distributed with this software.
  36 /* AUTHOR(S)
  37 /*      Wietse Venema
  38 /*      IBM T.J. Watson Research
  39 /*      P.O. Box 704
  40 /*      Yorktown Heights, NY 10598, USA
  41 /*--*/
  42
  43 /* System library. */
  44
  45 #include <sys_defs.h>
  46 #include <unistd.h>
  47 #include <fcntl.h>
  48
  49 /* Utility library. */
  50
  51 #include <msg.h>
  52 #include <vstream.h>
  53 #include <vstring.h>
  54 #include <safe_open.h>
  55 #include <myflock.h>
  56 #include <open_lock.h>
  57
  58 /* open_lock - open file and lock it for exclusive access */
  59
  60 VSTREAM *open_lock(const char *path, int flags, mode_t mode, VSTRING *why)
  61 {
  62     VSTREAM *fp;
  63
  64     /*
  65      * Carefully create or open the file, and lock it down. Some systems
  66      * don't have the O_LOCK open() flag, or the flag does not do what we
  67      * want, so we roll our own lock.
  68      */
  69     if ((fp = safe_open(path, flags, mode, (struct stat *) 0, -1, -1, why)) == 0)
  70         return (0);
  71     if (myflock(vstream_fileno(fp), INTERNAL_LOCK,
  72                 MYFLOCK_OP_EXCLUSIVE | MYFLOCK_OP_NOWAIT) < 0) {
  73         vstring_sprintf(why, "unable to set exclusive lock: %m");
  74         vstream_fclose(fp);
  75         return (0);
  76     }
  77     return (fp);
  78 }