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

   1 /*      $NetBSD$        */
   2
   3 /*++
   4 /* NAME
   5 /*      timed_write 3
   6 /* SUMMARY
   7 /*      write operation with pre-write timeout
   8 /* SYNOPSIS
   9 /*      #include <iostuff.h>
  10 /*
  11 /*      ssize_t timed_write(fd, buf, len, timeout, context)
  12 /*      int     fd;
  13 /*      const void *buf;
  14 /*      size_t  len;
  15 /*      int     timeout;
  16 /*      void    *context;
  17 /* DESCRIPTION
  18 /*      timed_write() performs a write() operation when the specified
  19 /*      descriptor becomes writable within a user-specified deadline.
  20 /*
  21 /*      Arguments:
  22 /* .IP fd
  23 /*      File descriptor in the range 0..FD_SETSIZE.
  24 /* .IP buf
  25 /*      Write buffer pointer.
  26 /* .IP len
  27 /*      Write buffer size.
  28 /* .IP timeout
  29 /*      The deadline in seconds. If this is <= 0, the deadline feature
  30 /*      is disabled.
  31 /* .IP context
  32 /*      Application context. This parameter is unused. It exists only
  33 /*      for the sake of VSTREAM compatibility.
  34 /* DIAGNOSTICS
  35 /*      When the operation does not complete within the deadline, the
  36 /*      result value is -1, and errno is set to ETIMEDOUT.
  37 /*      All other returns are identical to those of a write(2) operation.
  38 /* LICENSE
  39 /* .ad
  40 /* .fi
  41 /*      The Secure Mailer license must be distributed with this software.
  42 /* AUTHOR(S)
  43 /*      Wietse Venema
  44 /*      IBM T.J. Watson Research
  45 /*      P.O. Box 704
  46 /*      Yorktown Heights, NY 10598, USA
  47 /*--*/
  48
  49 /* System library. */
  50
  51 #include <sys_defs.h>
  52 #include <unistd.h>
  53 #include <errno.h>
  54
  55 /* Utility library. */
  56
  57 #include <msg.h>
  58 #include <iostuff.h>
  59
  60 /* timed_write - write with deadline */
  61
  62 ssize_t timed_write(int fd, void *buf, size_t len,
  63                             int timeout, void *unused_context)
  64 {
  65     ssize_t ret;
  66
  67     /*
  68      * Wait for a limited amount of time for something to happen. If nothing
  69      * happens, report an ETIMEDOUT error.
  70      *
  71      * XXX Solaris 8 read() fails with EAGAIN after read-select() returns
  72      * success. The code below exists just in case their write implementation
  73      * is equally broken.
  74      *
  75      * This condition may also be found on systems where select() returns
  76      * success on pipes with less than PIPE_BUF bytes of space, and with
  77      * badly designed software where multiple writers are fighting for access
  78      * to the same resource.
  79      */
  80     for (;;) {
  81         if (timeout > 0 && write_wait(fd, timeout) < 0)
  82             return (-1);
  83         if ((ret = write(fd, buf, len)) < 0 && timeout > 0 && errno == EAGAIN) {
  84             msg_warn("write() returns EAGAIN on a writable file descriptor!");
  85             msg_warn("pausing to avoid going into a tight select/write loop!");
  86             sleep(1);
  87             continue;
  88         } else if (ret < 0 && errno == EINTR) {
  89             continue;
  90         } else {
  91             return (ret);
  92         }
  93     }
  94 }