Re: Wireshark and serial ports

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On Wed, Aug 23, 2023 at 5:21 PM Steve Underwood <coppice12@xxxxxxxxx> wrote:
> Has anyone used wireshark while using USB serial ports with Fedora 37?
> As soon as I start wireshark the communication on my serial ports
> breaks. Thinking this might be something to do with wireshark scanning
> for available interfaces, I tried starting wireshark with "wireshark -i
> enp3c0", but it still seems to list all the interfaces, and it still
> messes up my serial communication. I'm sure I was doing things like this
> in 2022 without any trouble.

I have not found myself in your position, so I can't comment on
Wireshark and serial ports.

But I have been in the position of NetworkManager messing with my
serial ports. To work around it in my code, I made the file descriptor
exclusive so NetworkManager could not open it:

    /* Open the modem. It will be configured for exclusive use below. */
    s_modem = open(device_path, O_RDWR | O_NOCTTY | O_SYNC);
    ret = errno;
    if (s_modem == -1) {
        log_error("Failed to open device %s: %s\n", device_path,
        s_modem = 0; errno = ret;
        goto finished;

    /* Verify the modem is a terminal we can configure and control */
    if (!isatty(s_modem))
        log_error("Device %s is not a tty\n", device_path);
        close(s_modem); s_modem = 0;
        ret = errno = ENOTTY;
        goto finished;

    /* Get exclusive access to the modem. */
    /* Don't allow NetworkManager and ModemManager access */
    if (ioctl(s_modem, TIOCEXCL, NULL) == -1) {
        log_warn("Failed to set TIOCEXCL on device: %s\n", strerror(errno));

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