freebsd stable - Aug 2014 - Support DISCARD (^O)

On Aug 12, 2014, at 2:44 PM, John Baldwin <jhb at FreeBSD.org> wrote:
> 
> -- 
> John Baldwin
> 
> From: Eivind Nicolay Evensen <eivinde at terraplane.org>
> Subject: Re: Support DISCARD (^O)
> Date: July 5, 2014 at 4:34:16 AM MDT
> To: freebsd-stable at freebsd.org
> 
> 
> On Tue, Dec 17, 2013 at 10:18:16PM +0100, Eivind Evensen wrote:
>> Hello.
>> 
>> I don't know if there is any particular reason that support for
DISCARD/^O
>> was not included in the tty rewrite that happened from FreeBSD 7 to 8,
>> but in case anybody else wants it, here's a diff functioning mostly
>> like in 7, except output isn't switched back on automatically on
input.
>> 
>> Diff is against FreeBSD 8, however, last time I checked I didn't
see
>> much difference in the newer versions.
> 
> Here's a diff against FreeBSD 10. It seems to work fine there too.
> 
> 
> diff -r 59ad9c4b7916 -r 6e500f4552b4 sys/kern/tty_ttydisc.c
> --- a/sys/kern/tty_ttydisc.c	Fri Jul 04 17:27:59 2014 +0200
> +++ b/sys/kern/tty_ttydisc.c	Fri Jul 04 17:29:29 2014 +0200
> @@ -464,6 +464,9 @@
> 	if (tp->t_flags & TF_ZOMBIE)
> 		return (EIO);
> 
> +	if (tp->t_termios.c_lflag & FLUSHO)
> +		return (0);
> +
> 	/*
> 	 * We don't need to check whether the process is the foreground
> 	 * process group or if we have a carrier. This is already done
> @@ -896,6 +899,14 @@
> 
> 	/* Special control characters that are implementation dependent. */
> 	if (CMP_FLAG(l, IEXTEN)) {
> +		/* Discard (^O) */
> +		if (CMP_CC(VDISCARD, c)) {
> +			if (!(tp->t_termios.c_lflag & FLUSHO))
> +				ttyoutq_write_nofrag(&tp->t_outq, "^O", 2);
> +			tp->t_termios.c_lflag ^= FLUSHO;
> +			return(0);
> +		}
> +
DISCARD is supposed to turn back off after any character that you type, not just
^O again.

Warner

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On Tue, 12 Aug 2014, 17:12 -0600, Warner Losh wrote:
> On Aug 12, 2014, at 2:44 PM, John Baldwin <jhb at FreeBSD.org> wrote:
> > From: Eivind Nicolay Evensen <eivinde at terraplane.org>
> > Date: July 5, 2014 at 4:34:16 AM MDT
> > On Tue, Dec 17, 2013 at 10:18:16PM +0100, Eivind Evensen wrote:
> >> 
> >> I don't know if there is any particular reason that support
for DISCARD/^O
> >> was not included in the tty rewrite that happened from FreeBSD 7
to 8,
> >> but in case anybody else wants it, here's a diff functioning
mostly
> >> like in 7, except output isn't switched back on automatically
on input.
> >> 
> >> Diff is against FreeBSD 8, however, last time I checked I
didn't see
> >> much difference in the newer versions.
> > 
> > Here's a diff against FreeBSD 10. It seems to work fine there too.
> DISCARD is supposed to turn back off after any character that you type, not
just ^O again.
Irrespective of exactly how it's implemented, I'd love to see this.
Coming from a VMS background, I was used to a ^O toggle.  I reach for ^O
whenever I unintentionally initiate a huge stream of terminal output
over a WAN link.

-- 
John Marshall
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