From owner-freebsd-net  Sat Jun  1  7:48:40 2002
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Date: Sun, 2 Jun 2002 00:51:56 +1000 (EST)
From: Bruce Evans <bde@zeta.org.au>
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To: Archie Cobbs <archie@dellroad.org>
Cc: Julian Elischer <julian@elischer.org>,
	Bosko Milekic <bmilekic@unixdaemons.com>, <freebsd-net@FreeBSD.ORG>
Subject: Re: m_split() considered harmful
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On Fri, 31 May 2002, Archie Cobbs wrote:

> That is, what we really need is a more general audit for code that
> writes into mbufs that might be read-only -- and, as one special case
> of tha, code that calls M_TRAILINGSPACE()/M_LEADINGSPACE() before writing
> into an mbuf.
>
> FYI, any easy way to do this would be to add const'ness to mtod():
>
>     #define mtod(m, t)  ((const t)((m)->m_data))
>
> and then look for GCC warnings. Any takers?? :-)

This assumes that t is literally a pointer.  When t is caddr_t,
`const t' is a const variable which (if caddr_t is `char *') is a
pointer to non-const storage, but you want a non-const pointer to
const storage.

Bruce


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