Add missing POSIX 1003.1-2008 open(2) flag; O_TTY_INIT.

On FreeBSD, this is the default behaviour. According to the spec, we may
give this flag a value of zero, but I'd rather not do this. If we define
it to a non-zero value, we can always change default behaviour without
changing the ABI. This is very unlikely to happen, though.

lib/libc/sys/open.2

@@ -28,7 +28,7 @@
 .\"     @(#)open.2	8.2 (Berkeley) 11/16/93
 .\" $FreeBSD$
 .\"
-.Dd April 10, 2008
+.Dd February 28, 2009
 .Dt OPEN 2
 .Os
 .Sh NAME
@@ -116,6 +116,7 @@ O_FSYNC		synchronous writes
 O_SYNC		synchronous writes
 O_NOFOLLOW	do not follow symlinks
 O_NOCTTY	don't assign controlling terminal
+O_TTY_INIT	restore default terminal attributes
 .Ed
 .Pp
 Opening a file with
@@ -208,6 +209,19 @@ The
 system call will not assign controlling terminals on
 .Fx .
 .Pp
+.Dv O_TTY_INIT
+may be used to ensure the OS restores the terminal attributes when
+initially opening a TTY.
+This is the default on
+.Fx ,
+but is present for
+.Tn POSIX
+compatibility.
+The initial call to
+.Fn open
+on a TTY will always restore default terminal attributes on
+.Fx .
+.Pp
 If successful,
 .Fn open
 returns a non-negative integer, termed a file descriptor.

sys/sys/fcntl.h

@@ -140,6 +140,11 @@ typedef	__pid_t		pid_t;
 #define	FEXEC		O_EXEC
 #endif
 
+/* Defined by POSIX 1003.1-2008; BSD default, but reserve for future use. */
+#if __POSIX_VISIBLE >= 200809
+#define	O_TTY_INIT	0x00080000	/* Restore default termios attributes */
+#endif
+
 /*
  * XXX missing O_DSYNC, O_RSYNC.
  */