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List:       linux-usb
Subject:    Re: g_serial hangs on write when the cable is disconnected
From:       Greg KH <greg () kroah ! com>
Date:       2015-08-05 14:56:27
Message-ID: 20150805145627.GA610 () kroah ! com
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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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