netdev - Re: [RFC PATCH] net: Add support for virtual machine device queues (VMDQ)

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Date:	Fri, 20 Jul 2012 19:01:20 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	John Fastabend <john.r.fastabend@...el.com>
CC:	Jiri Pirko <jiri@...nulli.us>, <or.gerlitz@...il.com>,
	<davem@...emloft.net>, <roland@...nel.org>,
	<netdev@...r.kernel.org>, <ali@...lanox.com>,
	<sean.hefty@...el.com>, <shlomop@...lanox.com>,
	"Ronciak, John" <john.ronciak@...el.com>
Subject: Re: [RFC PATCH] net: Add support for virtual machine device queues
 (VMDQ)

On Fri, 2012-07-20 at 09:30 -0700, John Fastabend wrote:
> On 7/18/2012 11:42 PM, Jiri Pirko wrote:
> > Thu, Jul 19, 2012 at 12:05:44AM CEST, john.r.fastabend@...el.com wrote:
> >> This adds support to allow virtual net devices to be created. These
> >> devices can be managed independtly of the physical function but
> >> use the same physical link.
> 
> [...]
> 
> >> +
> >> +size_t vmdq_getpriv_size(struct net *src_net, struct nlattr *tb[])
> >> +{
> >> +	struct net_device *lowerdev;
> >> +
> >> +	if (!tb[IFLA_LINK])
> >> +		return -EINVAL;
> >> +
> >> +	lowerdev = __dev_get_by_index(src_net, nla_get_u32(tb[IFLA_LINK]));
> >> +	if (!lowerdev)
> >> +		return -ENODEV;
> >> +
> >> +	return sizeof(netdev_priv(lowerdev));
> >> +}
> >
> > Why exactly do you need to have the priv of same size as lowerdev? I do
> > not see you use that anywhere...
> >
> 
> When we add a child device the hardware/sw may have some private data
> it needs to manage this device.
> 
> I made an assumption here that the priv space for child devices is the
> same as the lowerdev but this might be a bad assumption.

The code assumes that it is the size of a single pointer...

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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