Date: Tue, 26 Aug 2008 19:36:39 +0300 From: Giorgos Keramidas <keramida@freebsd.org> To: Ed Schouten <ed@80386.nl> Cc: FreeBSD Current <freebsd-current@freebsd.org> Subject: Re: Inserting flow-control chars with an mpsafetty kernel Message-ID: <87fxorlomg.fsf@kobe.laptop> In-Reply-To: <20080826160144.GG99951@hoeg.nl> (Ed Schouten's message of "Tue, 26 Aug 2008 18:01:44 %2B0200") References: <87fxot5hoi.fsf@kobe.laptop> <20080826160144.GG99951@hoeg.nl>
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On Tue, 26 Aug 2008 18:01:44 +0200, Ed Schouten <ed@80386.nl> wrote: > * Giorgos Keramidas <keramida@ceid.upatras.gr> wrote: >> After installing the mpsafetty changes it seems that flow-control ^S and >> ^Q characters cannot be inserted inserted anymore. I first noticed this >> when CTRL-S stopped working as 'search-forward' in Emacs, but it seems >> the same problem exists in /usr/bin/vi, vim, bash and a few other >> programs that I tested. >> >> With a kernel before the mpsafetty changes, I can fire up /usr/bin/vi >> and type in insert-mode `^V^S'. This correctly inserts a ^S character. >> With a kernel from svn revision /head@181939 ^V no longer quotes the >> next byte in vi(1) and other programs. > > There is indeed a small problem w.r.t. ^S/^Q characters with the MPSAFE > TTY code, but it is not so directly involved in the handling of the > actual characters, but a shortcoming of the pts(4) driver. > > There is this way a PTY (master device) can be configured to use `packet > mode' (TIOCPKT). When this mode is enabled, all data that is read() by > screen is prepended by a single byte, containing a bit mask of events. > These events include flush events, but also flags indicating tcsetattr() > has been called and has toggled VSTART/VSTOP. [snip explanation of packet mode] > Screen(1) is a fairly moronic written application, which uses packet > mode for no sensible reason at all. If you just comment out TIOCPKT in > /usr/include/sys/ttycom.h and recompile screen(1), your problems are > gone, right? I'll give it a try and email back. Thanks! :) > There are three ways ways to fix this problem: > > - Implement a real packet mode which properly returns the TIOCPKT_* > flags. Unlike the previous TTY layer, it is a lot harder to do this > with MPSAFE TTY, because it turns the generic TTY code into more > bloat. > > The new TTY layer has been designed to be a real front-end for the > device driver. There aren't any driver hooks (yet) to detect the > events supported by TIOCPKT, because `normal drivers' don't need these > event notifications anyway. > > - Remove TIOCPKT and TIOCPKT_* to <sys/ioctl_compat.h> and leave it > there to die. While there, also move definitions of other awkward > commands to this header. > > - Both. > > I was planning to prepare a changeset soonish, which removes the (in > my opinion) deprecated ioctl()'s from our header files, so I can let > the ports folks run a tinderbox to see how much breaks. This should > give us a good estimation of the best approach. I can definitely rebuild `screen' with a commented out `TIOCPKT'. On the laptop I'm testing FreeBSD stuff I also have about 620 ports that I can rebuild with `portupgrade -fa' in a day or so. If you want me to test a patch that moves TIOCPKT_* to <sys/ioctl_compat.h> please count me in as a tester.
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