[PATCH] termios.3: Clarify ONLRET

[Simon Branch <simonmbranch@gmail.com>]

While perusing various termios(3) and termios(4) manpages, I noticed the
following inconsistency for ONLRET.  FreeBSD and NetBSD say this:

   If ONLRET is set, the NL character is assumed to do the carriage-return
   function; the column pointer will be set to 0.

OpenBSD says this:

   If ONLRET is set, NL also performs CR on output, and reset current column
   to 0.

POSIX says this:

   NL performs CR function.

The current Linux manpage says this (!):

   Don't output CR.

Here's a snippet that demonstrates Linux's behavior (tl;dr it's just like the
other operating systems):

   $ stty -icanon -onlcr -icrnl -echo onlret onocr; cat
   this is some text			(^J pressed)
                    and some more	(^M pressed before additional text)

The first flags (-icanon -onlcr -icrnl -echo), combined with cat, ensure that
our keys are sent directly back to the terminal emulator without any translation
or buffering.  The last two (ONLRET and ONOCR) are the important ones: ONLRET
makes Linux think that the cursor is at column 0 after the ^J, and ONOCR makes
Linux ignore the following ^M.

---
 man3/termios.3 | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/man3/termios.3 b/man3/termios.3
index c11937458..20641f14d 100644
--- a/man3/termios.3
+++ b/man3/termios.3
@@ -203,7 +203,9 @@ Map CR to NL on output.
 Don't output CR at column 0.
 .TP
 .B ONLRET
-Don't output CR.
+The NL character is assumed to do the carriage-return function;
+the kernel's idea of the current column is set to 0
+after both NL and CR.
 .TP
 .B OFILL
 Send fill characters for a delay, rather than using a timed delay.
-- 
2.34.0

---
 man3/termios.3 | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/man3/termios.3 b/man3/termios.3
index c11937458..20641f14d 100644
--- a/man3/termios.3
+++ b/man3/termios.3
@@ -203,7 +203,9 @@ Map CR to NL on output.
 Don't output CR at column 0.
 .TP
 .B ONLRET
-Don't output CR.
+The NL character is assumed to do the carriage-return function;
+the kernel's idea of the current column is set to 0
+after both NL and CR.
 .TP
 .B OFILL
 Send fill characters for a delay, rather than using a timed delay.
-- 
2.34.1