Re: [dpdk-dev] [PATCH] mbuf: fix compile by making sched struct visible

["Van Haaren, Harry" <harry.van.haaren@intel.com>]

> -----Original Message-----
> From: Thomas Monjalon [mailto:thomas@monjalon.net]
> Sent: Thursday, January 10, 2019 5:35 PM
> To: Van Haaren, Harry <harry.van.haaren@intel.com>
> Cc: dev@dpdk.org; Pattan, Reshma <reshma.pattan@intel.com>; Dumitrescu,
> Cristian <cristian.dumitrescu@intel.com>; olivier.matz@6wind.com
> Subject: Re: [PATCH] mbuf: fix compile by making sched struct visible
> 
> 10/01/2019 17:50, Harry van Haaren:
> > Although C compilation works with the struct rte_mbuf_sched
> > declared inside the struct rte_mbuf namespace, C++ fails to
> > compile. This fix moves the rte_mbuf_sched struct up to the
> > global namespace, instead of declaring it inside the struct
> > mbuf namespace.
> >
> > The struct rte_mbuf_sched is being used on the stack in
> > rte_mbuf_sched_get() and as a cast in _set(). For this
> > reason, it must be exposed as an available type.
> >
> > Fixes: 5d3f72100904 ("mbuf: implement generic format for sched field")
> >
> > Signed-off-by: Harry van Haaren <harry.van.haaren@intel.com>
> >
> > ---
> >
> > Cc: reshma.pattan@intel.com
> > Cc: cristian.dumitrescu@intel.com
> > Cc: thomas@monjalon.net
> >
> > Hey folks,
> >
> > Currently the mbuf header will fail to compile with a C++ compiler,
> > this patch is one possible solution. I'm not particularly happy with
> > this as a fix as it reduces mbuf struct readability, however it does
> > resolve the issue.
> 
> What are the other possible solutions?


I guess we could avoid using the struct in inline functions, by reading
or writing from the mbuf struct directly (without pulling out a temporary
rte_mbuf_sched field):

get()
*queue_id = m->hash.sched.queue_id;
...

set()
m->hash.sched.queue_id = queue_id;
...


I believe this was discussed when the patch was being reviewed;
http://patches.dpdk.org/patch/49126/

I have a mild preference to keep all mbuf structs visible inside the unions,
it makes it easier to understand the layout of mbuf, hence I prefer the
above pseudo code suggestion over the v1 patch sent before.

If others have a strong opinion for another solution, I'm ok with it.