Path: utzoo!mnetor!uunet!oddjob!ncar!ames!ucsd!sdcc6!sdcc7!muller
From: muller@sdcc7.ucsd.EDU (Keith Muller)
Newsgroups: comp.unix.wizards
Subject: Re: Pty ports and TIOCUCNTL mode
Message-ID: <1013@sdcc7.ucsd.EDU>
Date: 17 Apr 88 17:21:56 GMT
References: <576@modular.UUCP>
Distribution: comp
Organization: University of California, San Diego
Lines: 20
Summary: TIOCUCNTL Use



On 4.3 BSD this changes the reads on the master side pty to always be
preceeded by a extra byte. If the first byte on a read is a 0, then the
rest of the data is the result of a write on the slave side. A nonzero
first byte is the user ioctl sent. For example here are two ioctls for this
mode. WHen a slave side process does a ioctl(0, JBOOT, 0) the master
side on a read will see  (JBOOT&0xff) as the first byte. JMPX is a special
case and is not passed through, it is used to detect is a psuedo port is
in the TIOCUCNTL mode. 

#define	JBOOT		_IO(u, 1)
#define	JMPX		_IO(u, 0)

Watch out though, sun for example has decided to use this mode for
its on purposes and it it does not work this way. 

	Keith Muller
	University of California
	muller@ucsd.edu