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

   1 /*      $NetBSD$        */
   2
   3 /*++
   4 /* NAME
   5 /*      deliver_flock 3
   6 /* SUMMARY
   7 /*      lock open file for mail delivery
   8 /* SYNOPSIS
   9 /*      #include <deliver_flock.h>
  10 /*
  11 /*      int     deliver_flock(fd, lock_style, why)
  12 /*      int     fd;
  13 /*      int     lock_style;
  14 /*      VSTRING *why;
  15 /* DESCRIPTION
  16 /*      deliver_flock() sets one exclusive kernel lock on an open file,
  17 /*      for example in order to deliver mail.
  18 /*      It performs several non-blocking attempts to acquire an exclusive
  19 /*      lock before giving up.
  20 /*
  21 /*      Arguments:
  22 /* .IP fd
  23 /*      A file descriptor that is associated with an open file.
  24 /* .IP lock_style
  25 /*      A locking style defined in myflock(3).
  26 /* .IP why
  27 /*      A null pointer, or storage for diagnostics.
  28 /* DIAGNOSTICS
  29 /*      deliver_flock() returns -1 in case of problems, 0 in case
  30 /*      of success. The reason for failure is returned via the \fIwhy\fR
  31 /*      parameter.
  32 /* CONFIGURATION PARAMETERS
  33 /*      deliver_lock_attempts, number of locking attempts
  34 /*      deliver_lock_delay, time in seconds between attempts
  35 /*      sun_mailtool_compatibility, disable kernel locking
  36 /* LICENSE
  37 /* .ad
  38 /* .fi
  39 /*      The Secure Mailer license must be distributed with this software.
  40 /* AUTHOR(S)
  41 /*      Wietse Venema
  42 /*      IBM T.J. Watson Research
  43 /*      P.O. Box 704
  44 /*      Yorktown Heights, NY 10598, USA
  45 /*--*/
  46
  47 /* System library. */
  48
  49 #include "sys_defs.h"
  50 #include <unistd.h>
  51
  52 /* Utility library. */
  53
  54 #include <vstring.h>
  55 #include <myflock.h>
  56 #include <iostuff.h>
  57
  58 /* Global library. */
  59
  60 #include "mail_params.h"
  61 #include "deliver_flock.h"
  62
  63 /* Application-specific. */
  64
  65 #define MILLION 1000000
  66
  67 /* deliver_flock - lock open file for mail delivery */
  68
  69 int     deliver_flock(int fd, int lock_style, VSTRING *why)
  70 {
  71     int     i;
  72
  73     for (i = 1; /* void */ ; i++) {
  74         if (myflock(fd, lock_style,
  75                     MYFLOCK_OP_EXCLUSIVE | MYFLOCK_OP_NOWAIT) == 0)
  76             return (0);
  77         if (i >= var_flock_tries)
  78             break;
  79         rand_sleep(var_flock_delay * MILLION, var_flock_delay * MILLION / 2);
  80     }
  81     if (why)
  82         vstring_sprintf(why, "unable to lock for exclusive access: %m");
  83     return (-1);
  84 }