12306 XPG4v2 slave pty behaviour should generally be disabled
Reviewed by: Robert Mustacchi <rm@fingolfin.org>
Change-ID: I7ccd399c22866f34dd20c6bb9d28e77ba4e24c67

*** 22,36 ****
  /*
   * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
   * Use is subject to license terms.
   */
  
  /*      Copyright (c) 1988 AT&T */
  /*        All Rights Reserved   */
  
- #pragma ident   "%Z%%M% %I%     %E% SMI"
- 
  #pragma weak _ptsname = ptsname
  #pragma weak _grantpt = grantpt
  #pragma weak _unlockpt = unlockpt
  
  #include "lint.h"
--- 22,38 ----
  /*
   * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
   * Use is subject to license terms.
   */
  
+ /*
+  * Copyright 2020 OmniOS Community Edition (OmniOSce) Association.
+  */
+ 
  /*      Copyright (c) 1988 AT&T */
  /*        All Rights Reserved   */
  
  #pragma weak _ptsname = ptsname
  #pragma weak _grantpt = grantpt
  #pragma weak _unlockpt = unlockpt
  
  #include "lint.h"
*** 131,140 ****
--- 133,181 ----
                  return (-1);
  
          return (0);
  }
  
+ /*
+  * XPG4v2 requires that open of a slave pseudo terminal device
+  * provides the process with an interface that is identical to
+  * the terminal interface.
+  *
+  * To satisfy this, in strict XPG4v2 mode, this routine also sends
+  * a message down the stream that sets a flag in the kernel module
+  * so that additional actions are performed when opening an
+  * associated slave PTY device. When this happens, modules are
+  * automatically pushed onto the stream to provide terminal
+  * semantics and those modules are then informed that they should
+  * behave in strict XPG4v2 mode which modifies their behaviour. In
+  * particular, in strict XPG4v2 mode, empty blocks will be sent up
+  * the master side of the stream rather than being suppressed.
+  *
+  * Most applications do not expect this behaviour so it is only
+  * enabled for programs compiled in strict XPG4v2 mode (see
+  * stdlib.h).
+  */
+ int
+ __unlockpt_xpg4(int fd)
+ {
+         int ret;
+ 
+         if ((ret = unlockpt(fd)) == 0) {
+                 struct strioctl istr;
+ 
+                 istr.ic_cmd = PTSSTTY;
+                 istr.ic_len = 0;
+                 istr.ic_timout = 0;
+                 istr.ic_dp = NULL;
+ 
+                 if (ioctl(fd, I_STR, &istr) < 0)
+                         ret = -1;
+         }
+ 
+         return (ret);
+ }
+ 
  int
  grantpt(int fd)
  {
          struct strioctl istr;
          pt_own_t pto;