mirror of https://github.com/wb2osz/direwolf.git
Fix two problems with KISS pseudo terminal interface.
(1) kissattach: Error setting line discipline: TIOCSETD: Device or resource busy (2) Hang, and other resulting problems, when -p command line option used but there was no application reading from the pseudo terminal.
This commit is contained in:
WB2OSZ
parent
b35a674204
commit
8b9c6fcf4a
149
kiss.c
149
kiss.c
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@ -1,7 +1,7 @@
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//
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// This file is part of Dire Wolf, an amateur radio packet TNC.
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//
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// Copyright (C) 2011, 2013, 2014 John Langner, WB2OSZ
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// Copyright (C) 2011, 2013, 2014, 2016 John Langner, WB2OSZ
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//
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// This program is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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@ -24,14 +24,13 @@
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* Module: kiss.c
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*
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* Purpose: Act as a virtual KISS TNC for use by other packet radio applications.
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* On Windows, it is a serial port. On Linux, a pseudo terminal.
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*
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* Input:
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*
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* Outputs:
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*
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* Description: This provides a pseudo terminal for communication with a client application.
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*
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* It implements the KISS TNC protocol as described in:
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* Description: It implements the KISS TNC protocol as described in:
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* http://www.ka9q.net/papers/kiss.html
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*
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* Briefly, a frame is composed of
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@ -355,7 +354,7 @@ static MYFDTYPE kiss_open_pt (void)
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char *pts;
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struct termios ts;
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int e;
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//int flags;
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#if DEBUG
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text_color_set(DW_COLOR_DEBUG);
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@ -397,39 +396,31 @@ static MYFDTYPE kiss_open_pt (void)
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}
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/*
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* After running for a while on Linux, the write eventually
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* blocks if no one is reading from the other side of
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* the pseudo terminal. We get stuck on the kiss data
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* write and reception stops.
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* We had a problem here since the beginning.
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* If no one was reading from the other end of the pseudo
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* terminal, the buffer space would eventually fill up,
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* the write here would block, and the receive decode
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* thread would get stuck.
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*
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* I tried using ioctl(,TIOCOUTQ,) to see how much was in
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* the queue but that always returned zero. (Ubuntu)
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*
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* Let's try using non-blocking writes and see if we get
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* the EWOULDBLOCK status instead of hanging.
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* March 2016 - A "select" was put before the read to
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* solve a different problem. With that in place, we can
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* now use non-blocking I/O and detect the buffer full
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* condition here.
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*/
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#if 0 // this is worse. all writes fail. errno = 0 bad file descriptor
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flags = fcntl(fd, F_GETFL, 0);
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// text_color_set(DW_COLOR_DEBUG);
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// dw_printf("Debug: Try using non-blocking mode for pseudo terminal.\n");
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int flags = fcntl(fd, F_GETFL, 0);
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e = fcntl (fd, F_SETFL, flags | O_NONBLOCK);
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if (e != 0) {
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text_color_set(DW_COLOR_ERROR);
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dw_printf ("Can't set pseudo terminal to nonblocking, fcntl returns %d, errno = %d\n", e, errno);
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perror ("pt fcntl");
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}
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#endif
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#if 0 // same
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flags = 1;
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e = ioctl (fd, FIONBIO, &flags);
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if (e != 0) {
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text_color_set(DW_COLOR_ERROR);
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dw_printf ("Can't set pseudo terminal to nonblocking, ioctl returns %d, errno = %d\n", e, errno);
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perror ("pt ioctl");
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}
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#endif
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text_color_set(DW_COLOR_INFO);
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dw_printf("Virtual KISS TNC is available on %s\n", pt_slave_name);
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dw_printf("WARNING - Dire Wolf will hang eventually if nothing is reading from it.\n");
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#if 1
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@ -633,12 +624,10 @@ static MYFDTYPE kiss_open_nullmodem (char *devicename)
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* flen - Length of raw received frame not including the FCS
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* or -1 for a text string.
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*
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*
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* Description: Send message to client.
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* We really don't care if anyone is listening or not.
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* I don't even know if we can find out.
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*
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*
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*--------------------------------------------------------------------*/
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@ -702,14 +691,12 @@ void kiss_send_rec_packet (int chan, unsigned char *fbuf, int flen)
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/* Pseudo terminal for Cygwin and Linux. */
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err = write (pt_master_fd, kiss_buff, (size_t)kiss_len);
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if (err == -1 && errno == EWOULDBLOCK) {
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#if DEBUG
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text_color_set (DW_COLOR_INFO);
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dw_printf ("KISS SEND - discarding message because write would block.\n");
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#endif
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dw_printf ("KISS SEND - Discarding message because no one is listening.\n");
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dw_printf ("This happens when you use the -p option and don't read from the pseudo terminal.\n");
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}
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else if (err != kiss_len)
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{
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@ -772,13 +759,6 @@ void kiss_send_rec_packet (int chan, unsigned char *fbuf, int flen)
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//nullmodem_fd = MYFDERROR;
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}
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#if DEBUG
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/* Could wait with GetOverlappedResult but we never */
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/* have an issues in this direction. */
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//text_color_set(DW_COLOR_DEBUG);
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//dw_printf ("KISS SEND completed. wrote %d / %d\n", nwritten, kiss_len);
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#endif
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#else
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err = write (nullmodem_fd, kiss_buf, (size_t)kiss_len);
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if (err != len)
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@ -796,20 +776,25 @@ void kiss_send_rec_packet (int chan, unsigned char *fbuf, int flen)
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/*-------------------------------------------------------------------
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*
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* Name: kiss_listen_thread
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* Name: kiss_get
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*
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* Purpose: Wait for messages from an application.
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* Purpose: Read one byte from the KISS client app.
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*
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* Global In: nullmodem_fd or pt_master_fd
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* Global In: nullmodem_fd (Windows) or pt_master_fd (Linux)
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*
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* Description: Process messages from the client application.
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* Returns: one byte (value 0 - 255) or terminate thread on error.
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*
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* Description: There is room for improvment here. Reading one byte
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* at a time is inefficient. We could read a large block
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* into a local buffer and return a byte from that most of the time.
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* Is it worth the effort? I don't know. With GHz processors and
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* the low data rate here it might not make a noticable difference.
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*
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*--------------------------------------------------------------------*/
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/* Return one byte (value 0 - 255) or terminate thread on error. */
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static int kiss_get (/* MYFDTYPE fd*/ void )
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{
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@ -884,18 +869,66 @@ static int kiss_get (/* MYFDTYPE fd*/ void )
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#else /* Linux/Cygwin version */
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int n = 0;
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fd_set fd_in;
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fd_set fd_in, fd_ex;
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int rc;
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while ( n == 0 ) {
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/* Reading from master fd of the pty before the client has connected leads to trouble with kissattach. */
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/* Use select to check if the slave has sent any data before trying to read from it. */
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/*
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* Since the beginning we've always had a couple annoying problems with
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* the pseudo terminal KISS interface.
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* When using "kissattach" we would sometimes get the error message:
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*
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* kissattach: Error setting line discipline: TIOCSETD: Device or resource busy
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* Are you sure you have enabled MKISS support in the kernel
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* or, if you made it a module, that the module is loaded?
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*
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* martinhpedersen came up with the interesting idea of putting in a "select"
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* before the "read" and explained it like this:
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*
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* "Reading from master fd of the pty before the client has connected leads
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* to trouble with kissattach. Use select to check if the slave has sent
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* any data before trying to read from it."
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*
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* "This fix resolves the issue by not reading from the pty's master fd, until
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* kissattach has opened and configured the slave. This is implemented using
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* select() to wait for data before reading from the master fd."
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*
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* The submitted code looked like this:
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*
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* FD_ZERO(&fd_in);
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* rc = select(pt_master_fd + 1, &fd_in, NULL, &fd_in, NULL);
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*
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* That doesn't look right to me for a couple reasons.
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* First, I would expect to use FD_SET for the fd.
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* Second, using the same bit mask for two arguments doesn't seem
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* like a good idea because select modifies them.
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* When I tried running it, we don't get the failure message
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* anymore but the select never returns so we can't read data from
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* the KISS client app.
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*
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* I think this is what we want.
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*
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* Tested on Raspian (ARM) and Ubuntu (x86_64).
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* We don't get the error from kissattach anymore.
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*/
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FD_ZERO(&fd_in);
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rc = select(pt_master_fd + 1, &fd_in, NULL, &fd_in, NULL);
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FD_SET(pt_master_fd, &fd_in);
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FD_ZERO(&fd_ex);
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FD_SET(pt_master_fd, &fd_ex);
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rc = select(pt_master_fd + 1, &fd_in, NULL, &fd_ex, NULL);
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#if 0
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text_color_set(DW_COLOR_DEBUG);
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dw_printf ("select returns %d, errno=%d, fd=%d, fd_in=%08x, fd_ex=%08x\n", rc, errno, pt_master_fd, *((int*)(&fd_in)), *((int*)(&fd_in)));
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#endif
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if (rc == 0)
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{
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continue;
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continue; // When could we get a 0?
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}
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if (rc == MYFDERROR
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@ -903,7 +936,7 @@ static int kiss_get (/* MYFDTYPE fd*/ void )
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{
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text_color_set(DW_COLOR_ERROR);
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dw_printf ("\nError receiving kiss message from client application. Closing %s.\n\n", pt_slave_name);
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dw_printf ("\nError receiving KISS message from client application. Closing %s.\n\n", pt_slave_name);
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perror ("");
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close (pt_master_fd);
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@ -938,6 +971,18 @@ static int kiss_get (/* MYFDTYPE fd*/ void )
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}
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/*-------------------------------------------------------------------
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*
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* Name: kiss_listen_thread
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*
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* Purpose: Read messages from serial port KISS client application.
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*
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* Global In: nullmodem_fd (Windows) or pt_master_fd (Linux)
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*
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* Description: Reads bytes from the KISS client app and
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* sends them to kiss_rec_byte for processing.
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*
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*--------------------------------------------------------------------*/
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static THREAD_F kiss_listen_thread (void *arg)
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