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

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Message-ID: <87twi4g8s2.fsf@linux.intel.com>
Date:	Wed, 11 May 2016 13:59:25 +0300
From:	Felipe Balbi <balbi@...nel.org>
To:	changbin.du@...el.com
Cc:	gregkh@...uxfoundation.org, mina86@...a86.com,
	rui.silva@...aro.org, k.opasiak@...sung.com, lars@...afoo.de,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	"Du\, Changbin" <changbin.du@...el.com>
Subject: Re: [PATCH] usb: gadget: f_fs: report error if excess data received


Hi,

changbin.du@...el.com writes:
> From: "Du, Changbin" <changbin.du@...el.com>
>
> Since the buffer size for req is rounded up to maxpacketsize,
> then we may end up with more data then user space has space
> for.

only for OUT direction with the controller you're using ;-)

> If it happen, we can keep the excess data for next i/o, or
> report an error. But we cannot silently drop data, because
> USB layer should ensure the data integrality it has transferred,
> otherwise applications may get corrupt data if it doesn't
> detect this case.

and when has this actually happened ? Host should not send more data in
this case, if it does, it's an error on the host side. Also, returning
-EOVERFLOW is not exactly correct here, because you'd violate POSIX
specification of read(), right ?

> Here, we simply report an error to userspace to let userspace
> proccess. Actually, userspace applications should negotiate

no, this violates POSIX. Care to explain what problem are you actually
facing ?

-- 
balbi

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