This is the mail archive of the
libc-alpha@sourceware.org
mailing list for the glibc project.
[patch] termios.3: Add missing details on behaviour of PARMRK
- From: Olivier TARTROU <olivier dot tartrou at gmail dot com>
- To: mtk dot manpages at gmail dot com
- Cc: linux-man at vger dot kernel dot org, libc-alpha at sourceware dot org
- Date: Thu, 5 Nov 2015 22:38:24 +0100
- Subject: [patch] termios.3: Add missing details on behaviour of PARMRK
- Authentication-results: sourceware.org; auth=none
For a serial terminal, with a specific configuration, input bytes with
value 0377 are passed to the program as two bytes, 0377 0377.
This (correct) behaviour is described in the documentation of the GNU
C Library (https://www.gnu.org/software/libc/manual/html_node/Input-Modes.html#Input-Modes)
but not in the termios.3 man page.
Problematic configuration: INPCK set, IGNPAR not set, PARMRK set,
ISTRIP not set.
This man page problem affects several users. Examples:
* http://sourceforge.net/p/ftdi-usb-sio/mailman/message/4079724/
* http://mailman.uclinux.org/pipermail/uclinux-dev/2006-November/040984.html
* ...
The patch below corrects this problem. This patch applies to release 4.02.
--- old/termios.3 2015-11-04 20:32:56.117200840 +0100
+++ new/termios.3 2015-11-04 23:31:23.165191198 +0100
@@ -36,6 +36,8 @@
.\" Added a section on canonical and noncanonical mode.
.\" Enhanced the discussion of "raw" mode for cfmakeraw().
.\" Document CMSPAR.
+.\" 2015-11-04, Olivier TARTROU <olivier.tartrou@gmail.com>:
+.\" Reworked description of PARMRK from
https://www.gnu.org/software/libc/manual/html_node/Input-Modes.html#Input-Modes
.\"
.TH TERMIOS 3 2015-03-02 "Linux" "Linux Programmer's Manual"
.SH NAME
@@ -133,8 +135,17 @@
Ignore framing errors and parity errors.
.TP
.B PARMRK
-If \fBIGNPAR\fP is not set, prefix a character with a parity error or
-framing error with \\377 \\0.
+If this bit is set, input bytes with parity or framing errors are
+marked when passed to the program. This bit is meaningful only when
+\fBINPCK\fP is set and \fBIGNPAR\fP is not set.
+The way erroneous bytes are marked is with two preceding bytes,
+\\377 and \\0. Thus, the program actually reads three bytes for one
+erroneous byte received from the terminal.
+If a valid byte has the value \\377, and \fBISTRIP\fP (see below) is
+not set, the program might confuse it with the prefix that marks a
+parity error. So a valid byte \\377 is passed to the program as two
+bytes, \\377 \\377, in this case.
+
If neither \fBIGNPAR\fP nor \fBPARMRK\fP
is set, read a character with a parity error or framing error
as \\0.
Best regards,
Olivier TARTROU