linux-kernel - Re: [PATCH] cdc-acm: some enhancement on acm delayed write

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Date:	Tue, 8 Apr 2014 15:52:47 +0200
From:	Johan Hovold <jhovold@...il.com>
To:	Oliver Neukum <oneukum@...e.de>
Cc:	Johan Hovold <jhovold@...il.com>, Xiao Jin <jin.xiao@...el.com>,
	gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, david.a.cohen@...ux.intel.com,
	yanmin.zhang@...el.com,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] cdc-acm: some enhancement on acm delayed write

> > > If I see this correctly, then ASYNCB_INITIALIZED is cleared in
> > > tty_port_close() we is called from acm_tty_close(). Thus it should
> > > be enough to make sure that the device is resumed at the beginning
> > > of acm_tty_close() and acm_resume() will do the job automatically.
> > > What do you think?
> > 
> > But the device should already be about to be resumed, right? If the port
> 
> Yes.
> 
> > is closed fast enough that resume hasn't had time to run before
> > shutdown is called I think the right thing to do is simply to discard
> > the delayed bytes (in shutdown).
> 
> I think if we said we have transmitted then we should do so.

We haven't made any such promises -- only that we've buffered the data.
Just like any write urb can be cancelled at close / shutdown before
having been transmitted.

The user needs to use closing_wait or drain_delay to give the buffers a
chance to empty. If not used at all, or we get a time out, then the data
should be discarded.

Johan
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