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List:       linux-usb
Subject:    g_serial hangs on write when the cable is disconnected
From:       Laszlo Papp <lpapp () kde ! org>
Date:       2015-08-05 10:05:56
Message-ID: CAOMwXhNwVKCK1+-q+fAgMc0ebpremXd+S1kUvZ9Ank-5BTMLCA () mail ! gmail ! com
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Hi,

The code below reproduces the issue. The code is intentionally kept
small, so it deliberately does not have error checking, et al.

Now, my concern is that it blocks for the write operation if the cable
is disconnected. This is not inline with the /dev/ttyS* operation, for
instance. They would not block if I disconnected the serial cable.

Is this a bug or feature? :-) If it turns out to be a feature, is it
better to use O_NONBLOCK if one does not want to use pthreads, etc?

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

int main()
{
    const char buf[] = "Hello World!\n";
    int fd = open("/dev/ttyGS0", O_RDWR | O_NONBLOCK);
    int sent = write(fd, buf, sizeof(buf)-1);
    close(fd);
    return 0;
}

Cheers, L.
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