Iain Hibbert wrote:
> Hi,
>    in sys/mbuf.h there exists some macros to store/extract private context
> information in a mbuf, so.
> 
> /*
>  * Allow drivers and/or protocols to use the rcvif member of
>  * PKTHDR mbufs to store private context information.
>  */
> #define	M_GETCTX(m, t)		((t) (m)->m_pkthdr.rcvif + 0)
> #define	M_SETCTX(m, c)		((void) ((m)->m_pkthdr.rcvif = (void *) (c)))
> 
> 
> is there a good reason for the '+ 0' in M_GETCTX? I get compiler
> complaints extracting a 'void *' because of the pointer arithmetic..

It prevents M_GETCTX to be used as an lvalue.
-- 
Matt Thomas                     email: matt@3am-software.com
3am Software Foundry              www: http://3am-software.com/bio/matt/
Cupertino, CA              disclaimer: I avow all knowledge of this message.