netdev - Re: [E1000-devel] [PATCH] e100: Fix inconsistency in bad frames handling

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Date:	Mon, 06 Jun 2011 22:29:57 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	Ben Greear <greearb@...delatech.com>,
	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
	Andrea Merello <andrea.merello@...il.com>,
	"e1000-devel@...ts.sourceforge.net" 
	<e1000-devel@...ts.sourceforge.net>, netdev@...r.kernel.org
Subject: Re: [E1000-devel] [PATCH] e100: Fix inconsistency in bad frames
 handling

Le lundi 06 juin 2011 à 21:15 +0100, Ben Hutchings a écrit :
> On Mon, 2011-06-06 at 10:56 -0700, Ben Greear wrote:
> > On 06/06/2011 10:49 AM, Brandeburg, Jesse wrote:
> > >
> > > <added netdev>, removed other useless lists.
> > >
> > > On Sat, 4 Jun 2011, Andrea Merello wrote:
> > >> In e100 driver it seems that the intention was to accept bad frames in
> > >> promiscuous mode and loopback mode.
> > >> I think this is evident because of the following code in the driver:
> > >>
> > >> if (nic->flags&  promiscuous || nic->loopback) {
> > >> 		config->rx_save_bad_frames = 0x1;	/* 1=save, 0=discard */
> > >> 		config->rx_discard_short_frames = 0x0;	/* 1=discard, 0=save */
> > >> 		config->promiscuous_mode = 0x1;		/* 1=on, 0=off */
> > >> 	}
> > >>
> > >
> > > Hi, thanks for your work on e100.
> > >
> > >> However this intention is not really realized because bad frames are
> > >> discarded later by SW check.
> > >> This patch finally honors the above intention, making the RX code to
> > >> let bad frames to pass when the NIC is in promiscuous or loopback
> > >> mode.
> > >
> > > I think this may be a mistake by the authors of the software developers
> > > manual.  The manual suggests that save bad frames and save short frames
> > > should be enabled in promisc mode, but all of our other drivers *do not*
> > > save bad frames when in promiscuous mode (by design).  This is intentional
> > > because a bad frame is just that, bad, and with no hope of knowing if the
> > > data in it is okay/malicious/other.  I understand your reasoning above,
> > > but realistically the rx_save_bad_frames should NOT be set.  I'd ack a
> > > patch to comment that line out.
> > >
> > >> This helped me a lot to debug an FPGA ethernet core.
> > >> Maybe it can be also useful to someone else..
> > >
> > > I think this patch is just that, debug only. As a developer I understand
> > > why this is useful, but there is no reason any normal user would be able
> > > to benefit from this, so for now, sorry:
> > >
> > > NACK.
> > 
> > I think anyone sniffing a funky network would have benefit in
> > receiving all frames.  So, while it shouldn't be enabled by default,
> > it would be nice to have an ethtool command to turn on receiving
> > bad-crc frames, as well as receiving the 4-byte CRC on the end of
> > the packets.
> > 
> > It just so happens I have such a patch, in case others agree :)
> 
> How would a received skb be flagged as having a CRC error?
> 

maybe some skb->pkt_type = PACKET_INVALID; or something...



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