linux-kernel - RE: [PATCH] usb: gadget: f_fs: report error if excess data received

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Message-ID: <87eg92p3cn.fsf@linux.intel.com>
Date:	Mon, 16 May 2016 15:57:44 +0300
From:	Felipe Balbi <felipe.balbi@...ux.intel.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	"Du\, Changbin" <changbin.du@...el.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	"gregkh\@linuxfoundation.org" <gregkh@...uxfoundation.org>,
	"mina86\@mina86.com" <mina86@...a86.com>,
	"rui.silva\@linaro.org" <rui.silva@...aro.org>,
	"k.opasiak\@samsung.com" <k.opasiak@...sung.com>,
	"lars\@metafoo.de" <lars@...afoo.de>,
	"linux-usb\@vger.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] usb: gadget: f_fs: report error if excess data received


Hi,

Alan Stern <stern@...land.harvard.edu> writes:
> On Fri, 13 May 2016, Felipe Balbi wrote:
>
>> We deliver to userspace the part userspace requested, right? So that's
>> okay. The USB details WRT e.g. babble or host trying to send more data
>> than expected, needs to be handled within the kernel.
>
> The point is that you don't know whether the host sent more data than
> expected.  All you know is that the host sent more data than the user
> asked the kernel for -- but maybe the user didn't ask for all the data
> that he expected.  Maybe the user wanted to retrieve the full set of
> data using two read() system calls.

right, but that just means we need to buffer the data instead of bailing
out of the first read() completely.

-- 
balbi

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