netdev - Re: [Xen-devel] xennet_start

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Date:   Fri, 20 Jan 2017 15:03:23 -0500
From:   Sowmini Varadhan <sowmini.varadhan@...cle.com>
To:     David Miller <davem@...emloft.net>
Cc:     Paul.Durrant@...rix.com, konrad.wilk@...cle.com,
        wei.liu2@...rix.com, netdev@...r.kernel.org,
        xen-devel@...ts.xenproject.org
Subject: Re: [Xen-devel] xennet_start_xmit assumptions

On (01/20/17 14:30), David Miller wrote:
> 
> CAP_SYS_RAWIO or not, the contract we have with the device is that
> there will be at least enough bytes to cover a link layer header.

I see. If that's the case (for all the kernel-driver interfaces), 
then the xen_netfront driver is probably not required to check for
variants of sk_buffs like pure-non-linear etc.

> This probably requires a little bit of an adjustment to the calling
> convention.  Perhaps:
> 
> 	int dev_validate_header(const struct net_device *dev,
> 				char *ll_header, int len);
> 
> So then you can go:
> 
> 	new_len = dev_validate_header(dev, skb->data, len);
> 	if (new_len < 0)
> 		goto out_cleanup_err;
> 	if (new_len > len)
> 		__skb_put(skb, new_len - len);
> 
> Or something like that.

ok let me work with that and get back (hopefully with an 
RFC patch).

--Sowmini