linux-kernel - Re: [RFC 1/2] n_tty: fix dropped output characters

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Message-ID: <20140414150438.2737893d@alan.etchedpixels.co.uk>
Date:	Mon, 14 Apr 2014 15:04:38 +0100
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	Oliver Neukum <oneukum@...e.de>
Cc:	Johan Hovold <jhovold@...il.com>, Jiri Slaby <jslaby@...e.cz>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	Peter Hurley <peter@...leysoftware.com>,
	Xiao Jin <jin.xiao@...el.com>, david.a.cohen@...ux.intel.com,
	yanmin.zhang@...el.com
Subject: Re: [RFC 1/2] n_tty: fix dropped output characters

On Mon, 14 Apr 2014 15:05:49 +0200
Oliver Neukum <oneukum@...e.de> wrote:

> On Mon, 2014-04-14 at 13:53 +0100, One Thousand Gnomes wrote:
> > On Fri, 11 Apr 2014 11:41:24 +0200
> > Johan Hovold <jhovold@...il.com> wrote:
> > 
> > > Fix characters being dropped by n_tty_write() due to a failure to
> > > check the return value of tty_put_char() in do_output_char().
> > > 
> > > Characters are currently being dropped by write if a tty driver claims
> > > to have write room available, but still fails to buffer any data
> > 
> > Your driver is buggy. If you advertise a buffer you must honour it and
> > neither shrink nor revoke it.
> 
> Is that a general rule or does it apply only till the next write?

Its a general rule. If you've advertised 5 bytes then you can only
advertise 0 after 5 bytes have been sent your way (or a hangup etc
occurred).

Alan
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