netdev - Re: Do I need to skb_put() Ethernet frames to a minimum of 60 bytes?

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Message-ID: <1344976557.2690.43.camel@bwh-desktop.uk.solarflarecom.com>
Date:	Tue, 14 Aug 2012 21:35:57 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Arvid Brodin <Arvid.Brodin@...n.com>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Nicolas Ferre <nicolas.ferre@...el.com>
Subject: Re: Do I need to skb_put() Ethernet frames to a minimum of 60 bytes?

On Tue, 2012-08-14 at 18:53 +0000, Arvid Brodin wrote:
> Hi,
> 
> If I create an sk_buff with a payload of less than 28 bytes (ethheader + data),
> and send it using the cadence/macb (Ethernet) driver, I get
> 
> eth0: TX underrun, resetting buffers
> 
> Now I know the minimum Ethernet frame size is 64 bytes (including the 4-byte
> FCS), but whose responsibility is it to pad the frame to this size if necessary?
> Mine or the driver's - i.e. should I just skb_put() to the minimum size or
> should I report the underrun as a driver bug?

If the hardware doesn't pad frames automatically then it's the driver's
reponsibility to do so.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
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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