[dpdk-dev] [PATCH v4 11/23] rte_mbuf.h: explicit cast restricting ptrdiff to uint16

[Ananyev, Konstantin]

> -----Original Message-----
> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Bruce Richardson
> Sent: Thursday, May 17, 2018 11:51 AM
> To: Andy Green <andy at warmcat.com>
> Cc: dev at dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v4 11/23] rte_mbuf.h: explicit cast restricting ptrdiff to uint16
> 
> On Mon, May 14, 2018 at 01:10:22PM +0800, Andy Green wrote:
> > /projects/lagopus/src/dpdk/build/include/rte_common.h:141:34:
> > warning: conversion from 'long unsigned int' to 'uint16_t'
> > {aka 'short unsigned int'} may change value [-Wconversion]
> >  #define RTE_PTR_DIFF(ptr1, ptr2) ((uintptr_t)(ptr1) -
> > (uintptr_t)(ptr2))
> >                                   ^
> > /projects/lagopus/src/dpdk/build/include/rte_mbuf.h:1360:13:
> > note: in expansion of macro 'RTE_PTR_DIFF'
> >   *buf_len = RTE_PTR_DIFF(shinfo, buf_addr);
> >
> > Signed-off-by: Andy Green <andy at warmcat.com>
> > ---
> >  lib/librte_mbuf/rte_mbuf.h |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> > index a27dbb878..0580ec8a0 100644
> > --- a/lib/librte_mbuf/rte_mbuf.h
> > +++ b/lib/librte_mbuf/rte_mbuf.h
> > @@ -1358,7 +1358,7 @@ rte_pktmbuf_ext_shinfo_init_helper(void *buf_addr, uint16_t *buf_len,
> >  	shinfo->fcb_opaque = fcb_opaque;
> >  	rte_mbuf_ext_refcnt_set(shinfo, 1);
> >
> > -	*buf_len = RTE_PTR_DIFF(shinfo, buf_addr);
> > +	*buf_len = (uint16_t)RTE_PTR_DIFF(shinfo, buf_addr);
> >  	return shinfo;
> >  }
> Acked-by: Bruce Richardson <bruce.richardson at intel.com>


Just as a nit: if all such conversions are unavoidable - might be introduce:
RTE_PTR_DIFF_TYPE(.., type)	((type)(RTE_PTR_DIFF(...))
Might look a bit nicer.
Konstantin