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@xxxxxxxxx>: +.\" 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 -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
