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List:       linux-serial
Subject:    Re: g_serial hangs on write when the cable is disconnected
From:       Alan Stern <stern () rowland ! harvard ! edu>
Date:       2015-08-05 18:15:47
Message-ID: Pine.LNX.4.44L0.1508051411090.1713-100000 () iolanthe ! rowland ! org
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On Wed, 5 Aug 2015, Greg KH wrote:

> hm, wait, is this really the n_gsm line discipline?  Or is it something
> else?
> 
> g_serial is the device side of a serial connection, there is no "cable
> removed" notification that it even knows about, that has to come from
> the gadget driver somehow, which you should listen for and then kick
> your userspace program.

There is the gserial_disconnect() callback, which gets invoked when the 
Vbus power (provided by the host) is removed.  It's a pretty good 
indicator that the USB cable has been unplugged.

I don't understand all the stuff that gserial_disconnect() does, but it 
ought to be more or less equivalent to a "hangup" -- as the kerneldoc 
says.  If it doesn't do what users expect, there's probably a bug 
somewhere.

Of course, it's possible that the callback does not get invoked in 
Laszlo's case.  Then the question would be: Why not?

Alan Stern

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