netdev - Re: r8169: fix driver drop incoming packets >= 1515 if MTU is set between 1515 and 1536

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Date:	Wed, 11 Nov 2009 20:15:36 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Raimonds Cicans <ray@...llo.lv>
Cc:	romieu@...zoreil.com, netdev@...r.kernel.org
Subject: Re: r8169: fix driver drop incoming packets >= 1515 if MTU is set
	between 1515 and 1536

On Wed, 2009-11-11 at 22:05 +0200, Raimonds Cicans wrote:
> Ben Hutchings:
> > On Wed, 2009-11-11 at 20:20 +0200, Raimonds Cicans wrote:
> >> Driver drop incoming packets >= 1515(1) if MTU is set between 1515(1) and 1536.
> >>
> >> 1) exact number depends on some factors:
> >> - VLAN tagged or not
> >> - patch "r8169: Fix card drop incoming VLAN tagged MTU byte large jumbo frames"
> >>   applied or not
> > [...]
> > 
> > MTU is a limit on transmission; it is not required to limit received
> > frames.
> 
> ???
> 
> In r8169 driver MTU is used to calculate receive buffer size.
> Receive buffer size is used to configure hardware incoming packet filter.
> 
> For jumbo frames:
> Receive buffer size = Max frame size = MTU + 14 (ethernet header) + 4
> (vlan header) + 4 (ethernet checksum) = MTU + 22
> 
> Bug:
> driver for all MTU up to 1536 use receive buffer size 1536
[...]

OK, now I understand.  The subject line you used is not grammatical and
I originally thought you considered it a bug that the driver might
accept packets with payload greater than MTU.

To make it clear, perhaps you could change the subject to:
'r8169: Fix receive buffer length when MTU is between 1515 and 1536'
and then explain the current behaviour below that.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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