Subject: Re: Select(S) in Xenix 386 2.3.2Newsgroups: comp.unix.xenixKeywords: select, serial, pipesReferences: <117@accsys.acc.uu.no> <172@prmmbx.UUCP>In article <172@prmmbx.UUCP>, csch@netcs.UUCP (Clemens Schrimpe) writes:> ivar@acc.uu.no (Ivar Hosteng) writes:> <> I have experienced some problems using the select call in Xenix 386 V2.3.2.> <> It does not seems to detect when a pipe gets ready to been read from.> This is, because there is no provision to select on pipes!> Why? The stuff is almost totally ported 1:1 from the Berkeley code and> in BSD pipes should consist of AF_UNIX sockets, on which you can naturally> select.> I was very angry, when I found this out after hours of digging with adb in> the kernel. But I also tried the same on a SUN under SunOS 4.0 and it doesn't> work either ... seems to be a common illness ???> (I wonder, because the code for that is very simple ... ??? ...)> > <> I also > <> have trouble using select on a serial port.  When I do that the input> <> turns into garbage.  This does not occur when I use select on the> <> multiscreen ttys (tty01-tty12).> Hehe - we had just the same!> Here is the solution (thanks to my colleague Stefan Koehler, who took one> look at my screen, into which I had starred for hours, to find it ...)> > Select is implemented by an undocumented ioctl> 	(0xFFFF == IOC_SELECT -> [sys/slect.h])> which is handled by ttiocom() for all devices using the standard> SYS-V linediscipline!> > The ioctl-routine for the serial devices [sioioctl()] just calls > ttiocom() [after some undefinable VPIX stuff ???] and> if it returns NON-ZERO it calls sioparam(), which adjusts certain> parameters and garbles the output!> OK so far. Now: The Bug lies in the ttiocom-code within the check> for IOC_SELECT. After detecting the IOC_SELECT, the ttiocom calls> the select-code and returns NOTHING, which means that if EAX is> non-zero (randomly) sioparam() is called and garbles the output.> > The Fix: (quick and dirty)> Write a routine called "ttiocom", which might look like this:> > ttiocom(ttyp, com, arg, flag)> struct tty *ttyp;> int com, arg, flag;	/* there should be better types for this :-) */> {> 	if (com == IOC_SELECT)> 	{> 		ttselect(ttyp, flag);> 		return(0);	/*** THIS IS IMPORTANT ***/> 	}> 	return(Ttiocom(ttyp, com ,arg, flag));> }> > Compile something like this, then use whatever you have (GNU-Emacs is> great in patching strings in binaries) to patch /usr/sys/sys/libsys.a> to change the original ttiocom into Ttiocom !> Link in your code and -by some magic reason- experience a full blown> select on your System V / Xenix machine!!!> > Have fun playing around with it -> > 	Clemens Schrimpe, netCS Informationstechnik GmbH Berlin> --> UUCP:		csch@netcs		BITNET:	csch@db0tui6.BITNET> ARPA/NSF:	csch@garp.mit.edu	PSI: PSI%45300033047::CSCH> PHONE:		+49-30-24 42 37		FAX: +49-30-24 38 00> BTX:		0303325016-0003		TELEX: 186672 net d