From mboxrd@z Thu Jan  1 00:00:00 1970
From: Thomas Monjalon <thomas.monjalon@6wind.com>
Subject: Re: [PATCH] examples: add ip version check for l3fwd app
Date: Wed, 03 Jun 2015 10:27:11 +0200
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To: "Chilikin, Andrey" <andrey.chilikin@intel.com>
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2015-06-03 08:24, Chilikin, Andrey:
> From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
> > 2015-05-15 17:08, Andrey Chilikin:
> > > Added optional ip version check to l3fwd app to allow to detect the ip
> > > version if mbuf ol_flags are not set in case of running in a VM with
> > > emulated network controllers
> > >
> > > Signed-off-by: Andrey Chilikin <andrey.chilikin@intel.com>
> > [...]
> > > +#define DO_IP_VERSION_CHECK             0
> > [...]
> > > @@ -953,6 +955,15 @@ l3fwd_simple_forward(struct rte_mbuf *m, uint8_t
> > portid, struct lcore_conf *qcon
> > >  	void *d_addr_bytes;
> > >  	uint8_t dst_port;
> > >
> > > +#if DO_IP_VERSION_CHECK
> > > +	if (!(m->ol_flags & (PKT_RX_IPV4_HDR | PKT_RX_IPV6_HDR))) {
> > > +		uint8_t ip_ver = *(uint8_t *)(rte_pktmbuf_mtod(m, unsigned
> > char *) +
> > > +			sizeof(struct ether_hdr)) >> 4;
> > > +		if (ip_ver == 4)
> > > +			m->ol_flags |= PKT_RX_IPV4_HDR;
> > > +	}
> > > +#endif
> > 
> > You are adding dead code. When ol_flags will be updated, it will be forget until
> > someone enables it.
> > In general, compile-time configurations are avoided and it's even worst when
> > this is hidden and not easily testable like here.
> 
> Agree, we already thinking about creating separate example l3fwd-vm to cover emulated network controllers.

Or you can try to implement some callbacks and choose the implementation
at init when detecting the environment.