Date: Tue, 27 May 2008 00:45:31 -0700 From: Julian Elischer <julian@elischer.org> To: Poul-Henning Kamp <phk@phk.freebsd.dk> Cc: Ed Schouten <ed@80386.nl>, current@FreeBSD.org, arch@FreeBSD.org, Robert Watson <rwatson@FreeBSD.org>, Ade Lovett <ade@FreeBSD.org>, net@FreeBSD.org, "Bruce M. Simpson" <bms@FreeBSD.org> Subject: Re: HEAD UP: non-MPSAFE network drivers to be disabled Message-ID: <483BBC1B.6040905@elischer.org> In-Reply-To: <42521.1211829076@critter.freebsd.dk>
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Poul-Henning Kamp wrote: > In message <20080526161608.GE64397@hoeg.nl>, Ed Schouten writes: > >> The new TTY layer should still support line disciplines, [...] > > Actually... I think it shouldn't. > > Line-disc's were introduced to interface weird-ass hardware like > digitizing tablets that had very high data rates, but very little > information (16 bit X, 16 bit Y and a couple of buttons, like modern > mice) which would cost inordinate amounts of CPU time to support > in userland on a VAX computer. > > If_slip.c happened in the kernel because there was no tun device, > people cranked the speed up all they could (Hands up: who has changed > the Xtal on a VAX serial port for faster SLIP ?) > > if_ppp happened because that was how if_slip did it. > > Today there is no longer a market for line disciplines and in > practice we have only one: the POSIX mandated "termios", which also > emulates the older "termio" ioctls. > > Anybody who cares to browse the three pages of text that RFC1055 > contains, will see that implementing SLIP in userland using tun(4) > and the code on the other three pages of RFC1055 is a trivial task > not even worthy of a SoC student. > > PPP over async is already much better handled in ppp(8) thanks > to Brians valiant effort back in the stoneage of the internet. > > We should summarily kill the concept of line disciplines as a > modular component and decide that TTYs can be used with termios(4) > or raw mode and leave it at that. > > Poul-Henning > However the line discipline was a very convenient place for netgraph to hook in without leaving the kernel. If you can supply an equally effective way to hook into a serial device in such a way that it appears to be a source/sink of bits then I don't care about line disciplins, but until you have a suggested replacement then leave them alone. There are MANY people using mpd with the netgraph ppp moduel hooked directly to the serial port via the netgraph line discipline.home | help
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