From mboxrd@z Thu Jan  1 00:00:00 1970
From: Greg KH <greg-U8xfFu+wG4EAvxtiuMwx3w@public.gmane.org>
Subject: Re: g_serial hangs on write when the cable is disconnected
Date: Wed, 5 Aug 2015 07:56:27 -0700
Message-ID: <20150805145627.GA610@kroah.com>
References: <CAOMwXhNwVKCK1+-q+fAgMc0ebpremXd+S1kUvZ9Ank-5BTMLCA@mail.gmail.com>
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To: Laszlo Papp <lpapp-RoXCvvDuEio@public.gmane.org>
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List-Id: linux-serial@vger.kernel.org

On Wed, Aug 05, 2015 at 11:05:56AM +0100, Laszlo Papp wrote:
> 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);

This line discipline is very different from the "traditional" tty line
discipline, so it might not know anything about cable removals.

good luck,

greg k-h
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