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

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Message-ID: <4DD53FDD.7070503@freescale.com>
Date:	Thu, 19 May 2011 11:05:49 -0500
From:	Timur Tabi <timur@...escale.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
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

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.

-- 
Timur Tabi
Linux kernel developer at Freescale

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