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

   1 /*      $NetBSD$        */
   2
   3 /*++
   4 /* NAME
   5 /*      write_wait 3
   6 /* SUMMARY
   7 /*      wait until descriptor becomes writable
   8 /* SYNOPSIS
   9 /*      #include <iostuff.h>
  10 /*
  11 /*      int     write_wait(fd, timeout)
  12 /*      int     fd;
  13 /*      int     timeout;
  14 /* DESCRIPTION
  15 /*      write_wait() blocks the current process until the specified file
  16 /*      descriptor becomes writable, or until the deadline is exceeded.
  17 /*
  18 /*      Arguments:
  19 /* .IP fd
  20 /*      File descriptor in the range 0..FD_SETSIZE.
  21 /* .IP timeout
  22 /*      If positive, deadline in seconds. A zero value effects a poll.
  23 /*      A negative value means wait until something happens.
  24 /* DIAGNOSTICS
  25 /*      Panic: interface violation. All system call errors are fatal.
  26 /*
  27 /*      A zero result means success.  When the specified deadline is
  28 /*      exceeded, write_wait() returns -1 and sets errno to ETIMEDOUT.
  29 /* LICENSE
  30 /* .ad
  31 /* .fi
  32 /*      The Secure Mailer license must be distributed with this software.
  33 /* AUTHOR(S)
  34 /*      Wietse Venema
  35 /*      IBM T.J. Watson Research
  36 /*      P.O. Box 704
  37 /*      Yorktown Heights, NY 10598, USA
  38 /*--*/
  39
  40 /* System library. */
  41
  42 #include <sys_defs.h>
  43 #include <sys/time.h>
  44 #include <signal.h>
  45 #include <errno.h>
  46 #include <unistd.h>
  47 #include <string.h>
  48
  49 #ifdef USE_SYSV_POLL
  50 #include <poll.h>
  51 #endif
  52
  53 #ifdef USE_SYS_SELECT_H
  54 #include <sys/select.h>
  55 #endif
  56
  57 /* Utility library. */
  58
  59 #include <msg.h>
  60 #include <iostuff.h>
  61
  62 /* write_wait - block with timeout until file descriptor is writable */
  63
  64 int     write_wait(int fd, int timeout)
  65 {
  66 #ifndef USE_SYSV_POLL
  67     fd_set  write_fds;
  68     fd_set  except_fds;
  69     struct timeval tv;
  70     struct timeval *tp;
  71
  72     /*
  73      * Sanity checks.
  74      */
  75     if (FD_SETSIZE <= fd)
  76         msg_panic("descriptor %d does not fit FD_SETSIZE %d", fd, FD_SETSIZE);
  77
  78     /*
  79      * Guard the write() with select() so we do not depend on alarm() and on
  80      * signal() handlers. Restart the select when interrupted by some signal.
  81      * Some select() implementations may reduce the time to wait when
  82      * interrupted, which is exactly what we want.
  83      */
  84     FD_ZERO(&write_fds);
  85     FD_SET(fd, &write_fds);
  86     FD_ZERO(&except_fds);
  87     FD_SET(fd, &except_fds);
  88     if (timeout >= 0) {
  89         tv.tv_usec = 0;
  90         tv.tv_sec = timeout;
  91         tp = &tv;
  92     } else {
  93         tp = 0;
  94     }
  95
  96     for (;;) {
  97         switch (select(fd + 1, (fd_set *) 0, &write_fds, &except_fds, tp)) {
  98         case -1:
  99             if (errno != EINTR)
 100                 msg_fatal("select: %m");
 101             continue;
 102         case 0:
 103             errno = ETIMEDOUT;
 104             return (-1);
 105         default:
 106             return (0);
 107         }
 108     }
 109 #else
 110
 111     /*
 112      * System-V poll() is optimal for polling a few descriptors.
 113      */
 114     struct pollfd pollfd;
 115
 116 #define WAIT_FOR_EVENT  (-1)
 117
 118     pollfd.fd = fd;
 119     pollfd.events = POLLOUT;
 120     for (;;) {
 121         switch (poll(&pollfd, 1, timeout < 0 ?
 122                      WAIT_FOR_EVENT : timeout * 1000)) {
 123         case -1:
 124             if (errno != EINTR)
 125                 msg_fatal("poll: %m");
 126             continue;
 127         case 0:
 128             errno = ETIMEDOUT;
 129             return (-1);
 130         default:
 131             if (pollfd.revents & POLLNVAL)
 132                 msg_fatal("poll: %m");
 133             return (0);
 134         }
 135     }
 136 #endif
 137 }