netdev - Re: ip_tables.h can't be used in C++ programs.

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Message-ID: <1282346230.3454.193.camel@localhost>
Date:	Sat, 21 Aug 2010 00:17:09 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Ben Greear <greearb@...delatech.com>
Cc:	NetDev <netdev@...r.kernel.org>
Subject: Re: ip_tables.h can't be used in C++ programs.

On Fri, 2010-08-20 at 11:54 -0700, Ben Greear wrote:
> This method returns void* but is defined to return
> a pointer to struct ipt_entry_target.
> 
> This will not compile under g++ (or, I'm unable to figure out
> how to make it work w/out editing the header file).
> 
> Any reason this shouldn't be changed to:
> 
>   return (struct ipt_entry_target*)e + e->target_offset;

Because that multiplies the offset by sizeof(struct ipt_entry_target)!

> /* Helper functions */
> static __inline__ struct ipt_entry_target *
> ipt_get_target(struct ipt_entry *e)
> {
>          return (void *)e + e->target_offset;
> }

For extra unportability, this is relying on the gcc extension for void
pointer arithmetic.  Try something like:

	return (struct ipt_entry_target *)((char *)e + e->target_offset);

Ben.

> IPv6 has similar issue....
> 
> Thanks,
> Ben
> 

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
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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