linux-kernel - Re: TTY loosing data with u

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Date:	Thu, 24 Mar 2011 12:51:45 +0000
From:	Toby Gray <toby.gray@...lvnc.com>
To:	balbi@...com
CC:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Stefan Bigler <stefan.bigler@...mile.com>,
	Greg KH <greg@...ah.com>, linux-kernel@...r.kernel.org,
	linux-usb@...r.kernel.org
Subject: Re: TTY loosing data with u_serial gadget

On 24/03/2011 12:37, Felipe Balbi wrote:
> Hi,
>
> On Thu, Mar 24, 2011 at 12:07:56PM +0000, Toby Gray wrote:
>> Is this patch missing the changes to tty_buffer.c that were in
>> http://permalink.gmane.org/gmane.linux.usb.general/28976
>>
>> Without the changes to tty_buffer.c to use the value returned from
>> the receive_buf call then doesn't this patch not work correctly?
>>
<snip>
> you are right, thanks for noticing that. Attached is an updated patch.
> I left removal of receive_room out of this patch to prevent too invasive
> change, that can be done on a separate patch.

I've just tried removing receive_room myself and noticed that it is 
still used in flush_to_ldisc to decide if it needs to schedule work to 
be done later:

    if (!tty->receive_room || seen_tail) {
       schedule_work(&tty->buf.work);
       break;
    }

If receive_room is no longer being updated then isn't this the wrong 
thing to do? Shouldn't it check if some data was copied after calling 
receive_buf, and if there wasn't any then it should schedule the work 
and break?

The other query I've got is about the return value from receive_buf. I 
noticed that you've modified some drivers (such as 
bluetooth/hci_ldisc.c) so that they can return error values, such as 
-ENODEV. Won't this cause things to go wrong when flush_to_ldisc and 
paste_selection use the return value without checking for it being negative?

Thank you for your quick reply to my first query, it's appreciated.

Regards,

Toby
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