Re: [PATCH] Improve behaviour of Netlink Sockets

On Fri, Sep 24, 2004 at 10:58:55AM -0700, David S. Miller wrote:

On Fri, 24 Sep 2004 16:26:04 +1000
Herbert Xu [off-list ref] wrote:

quoted

It also means those responders that can calculate the correct size
of the reply doesn't need to go through this copy process.

This is the crux of the problem, you don't know how big
the response will be until you look at the whole object
you are returning.

I understand.  What I'm saying is that some of these places already know
how big it is going to be.  See tcp_diag.c for an example.  So we shouldn't
impose the copy over head on everyone.

This is why I suggested the PAGE_SIZE scratchpad, you build
the response fully into there, then you know the exact size
SKB you need so you allocate it and copy into it from the
scratch pad.

I agree completely.  I'm just saying that the current NLM_GOODSIZE
skb is the perfect scratch-pad so we don't need a new one.  All we
need to do is to insert a helper call just before netlink_unicast
to copy and trim the packet in the places that need it.

Cheers,
-- 
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