netdev - Re: [RFC V2 PATCH] rtnetlink: Add method to calculate dump info data size

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Message-Id: <20110509.205828.104070242.davem@davemloft.net>
Date:	Mon, 09 May 2011 20:58:28 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	shemminger@...tta.com
Cc:	eric.dumazet@...il.com, gregory.v.rose@...el.com,
	netdev@...r.kernel.org, bhutchings@...arflare.com
Subject: Re: [RFC V2 PATCH] rtnetlink: Add method to calculate dump info
 data size

From: Stephen Hemminger <shemminger@...tta.com>
Date: Mon, 9 May 2011 20:56:26 -0700

> I was hoping that the new interface dump would not need a pre-calculated
> size and could just incrementally add values. I was trying to use an
> analogy with route dumping. The current route dump does not precalculate
> size.

Stephen the problem here is that one netdevice being dumped is highly
variable because of the VF netlink attributes.

Routes have a fixed reasonably low upper bound in size, so we always are
able to fit one route in an SKB.

Netdevices, on the other hand, can have so many VFs that one netdevice
entry does not fit even in a single 8K allocated SKB.

That's the failure case this code is trying to fix.
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