linux-kernel - Re: [PATCH 6/7] tty/powerpc: introduce the ePAPR embedded hypervisor byte channel driver

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Date:	Fri, 20 May 2011 10:54:17 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Timur Tabi <timur@...escale.com>
Cc:	<kumar.gala@...escale.com>, <benh@...nel.crashing.org>,
	<greg@...ah.com>, <akpm@...nel.org>,
	<linuxppc-dev@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>,
	<linux-console@...r.kernel.org>
Subject: Re: [PATCH 6/7] tty/powerpc: introduce the ePAPR embedded
 hypervisor byte channel driver

On Thu, 19 May 2011 11:05:49 -0500
Timur Tabi <timur@...escale.com> wrote:

> Alan Cox wrote:
> >> > +		/* Pass the received data to the tty layer.  Note that this
> >> > +		 * function calls tty_buffer_request_room(), so I'm not sure if
> >> > +		 * we should have also called tty_buffer_request_room().
> >> > +		 */
> >> > +		ret = tty_insert_flip_string(ttys, buffer, len);
> 
> > You only need to request_room in advance if you can't handle the case
> > where the insert_flip_string returns less than you stuffed down it.
> 
> If tty_insert_flip_string() returns less than I stuffed down it, the characters
> it didn't accept will be dropped.  That's because once I receive them, I have
> nowhere else to put them.  I suppose I could implement a receive FIFO, but that
> seems overkill.  If calling tty_buffer_request_room() ensures that
> tty_insert_flip_string() always accepts all the characters, I would rather do that.

I was answering the question in the comment in the code...

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