netdev - Re: [PATCH] usbnet: allow rx_process() to ignore packets

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Message-Id: <201009072202.18703.linux@rainbow-software.org>
Date:	Tue, 7 Sep 2010 22:02:16 +0200
From:	Ondrej Zary <linux@...nbow-software.org>
To:	David Brownell <david-b@...bell.net>
Cc:	David Brownell <dbrownell@...rs.sourceforge.net>,
	netdev@...r.kernel.org,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usbnet: allow rx_process() to ignore packets

On Sunday 05 September 2010 23:35:15 David Brownell wrote:
> > > > From: Ondrej Zary <linux@...nbow-software.org>
> > > > Subject: [PATCH] usbnet: allow rx_process() to
> >
> > ignore packets
> >
> > > It already can ... I'm already not
> > > liking this patch...
>
> You didn't explain why "ignore".  As a rule, if
> the network peer is sending garbage, that needs
> to be accounted as an error, not igored.  You seem
> to be complaining about accounting garbage as such.

It's not a garbage, just a packet that is not yet complete.

>  rx_process() knows only two cases:
> > either rx_fixup()
> > returns 0 or a non-zero value. If I return 0,
> >  the error counter is  incremented.
>
> So don't return zero, when you're not trying to
> indicate an error. ... easy.

If I return 1, the incomplete packet would be passed up the stack.

> > If I return non-zero value, packet is
> > processed ("passed up the
> > stack" - usbnet_skb_return() called)
> > if the skb has non-zero length,
>
> Exactly -- that's how the minidriver says that
> it stripped framing off the packet, so other
> code should pass the packet up the stack.
>
>
> Have you tried emptying the SKB (len zero) to
> indicate you've consumed all of its contents?
> (Or in your case, "ignored").  That would seem to
> be more like what you want to do ...  ISTR that the
> network stack cleanly handles empty SKBs; if not,
> maybe it should.

Yes, I have tried it - in fact, this is that cx82310_eth does now. It does not 
work because rx_process() in usbnet.c checks if the skb is empty - and 
increments the error counter if it is. Maybe it should not?

-- 
Ondrej Zary
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