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

@@ -22,15 +22,17 @@
 /*
  * 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 ident   "%Z%%M% %I%     %E% SMI"
-
 #pragma weak _ptsname = ptsname
 #pragma weak _grantpt = grantpt
 #pragma weak _unlockpt = unlockpt
 
 #include "lint.h"

@@ -131,10 +133,49 @@
                 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;