linux-kernel - Re: [PATCH] netfilter: replace horrible hack with ksize()

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Message-ID: <Pine.LNX.4.64.0803061618090.4378@sbz-30.cs.Helsinki.FI>
Date:	Thu, 6 Mar 2008 16:20:57 +0200 (EET)
From:	Pekka J Enberg <penberg@...helsinki.fi>
To:	Patrick McHardy <kaber@...sh.net>
cc:	Netfilter Development Mailinglist 
	<netfilter-devel@...r.kernel.org>, clameter@....com,
	joe@...ches.com, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org,
	Netfilter Development Mailinglist 
	<netfilter-devel@...r.kernel.org>
Subject: Re: [PATCH] netfilter: replace horrible hack with ksize()

On Thu, 6 Mar 2008, Pekka J Enberg wrote:
> > > -	if (newlen >= ct->ext->real_len) {
> > > +	if (newlen >= ksize(ct->ext)) {
> > 
> > This needs to look at the currently allocated size, otherwise
> > it will always realloc when adding new extensions after having
> > used up ksize(ct->ext) space.
> 
> Lets say you
> 
>   p = kmalloc(8, ...);
> 
> Then ksize(p) will return the currently allocated size which is 32 bytes 
> when page size is 4 KB, and not 8 bytes. So it should be equivalent of 
> what the current code does.
> 
> What am I missing here?

Ok, it's not equivalent. We have two sizes: object size (8 bytes) and 
buffer size (32 bytes) here. In netfilter, ->real_len is same as object 
size, not buffer size as ksize() is.

But now I am officially even more confused, why does the netfilter code 
decided whether to reallocate based on _object size_ and not _buffer size_ 
(as krealloc() does, for example)?

			Pekka
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