Date: Sun, 24 Dec 1995 02:45:37 +1100 From: Bruce Evans <bde@zeta.org.au> To: Mattias.Gronlund@sa.erisoft.se, freebsd-hackers@freebsd.org Subject: Re: Why XON/XOFF in /usr/sbin/ppp Message-ID: <199512231545.CAA28188@godzilla.zeta.org.au>
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> I have a question about why /usr/sbin/ppp in 2.1R have XON/XOFF enabled? >What I can se in the manpage for ppp it says that I should use Hardware >Handshake and when I try to connect to an Annex configured for dialback >I get some line-noice when the other side dissconnects to dialback. > One of these noice characters tend to be XOFF which make my FreeBSD >computer wait for an XON which will newer arrive, as an result the ppp >process hangs IO-wait so I can't kill it! But after disabling XON/XOFF >in /usr/sbin/ppp it works just like a charm! I think ppp sets IXON because it wants to be in a sort of terminal mode. I think ppp sets IXOFF because ppp is buggy. I think the hang is because the kernel (tty.c) is buggy. ppp switches off IXON and IXOFF when it enters packet mode but the kernel doesn't clear the associated flags or attempt to send a START character. This problem is even worse for the kernel-mode ppp and slip. IXOFF is probably handled OK as a side effect of flushing the buffer, but the flag associated with IXON (TS_TTSTOP) isn't cleared, and it is only cleared upon receipt of a START character (or any character if IXANY is set) in the standard line discipline, so it is never cleared in nonstandard line disciplines. Bruce
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