Re: [dpdk-dev] [PATCH v4 1/2] mbuf: support attaching external buffer to mbuf

[Olivier Matz <olivier.matz@6wind.com>]

On Wed, Apr 25, 2018 at 09:19:32AM +0000, Yongseok Koh wrote:
> > On Apr 25, 2018, at 2:08 AM, Yongseok Koh <yskoh@mellanox.com> wrote:
> >> On Apr 25, 2018, at 1:28 AM, Olivier Matz <olivier.matz@6wind.com> wrote:
> >> 
> >> Hi Yongseok,
> >> 
> >> On Tue, Apr 24, 2018 at 06:02:44PM +0200, Olivier Matz wrote:
> >>>>> @@ -688,14 +704,33 @@ rte_mbuf_to_baddr(struct rte_mbuf *md)
> >>>>> }
> >>>>> /**
> >>>>> + * Returns TRUE if given mbuf is cloned by mbuf indirection, or FALSE
> >>>>> + * otherwise.
> >>>>> + *
> >>>>> + * If a mbuf has its data in another mbuf and references it by mbuf
> >>>>> + * indirection, this mbuf can be defined as a cloned mbuf.
> >>>>> + */
> >>>>> +#define RTE_MBUF_CLONED(mb)     ((mb)->ol_flags & IND_ATTACHED_MBUF)
> >>>>> +
> >>>>> +/**
> >>>>>  * Returns TRUE if given mbuf is indirect, or FALSE otherwise.
> >>>>>  */
> >>>>> -#define RTE_MBUF_INDIRECT(mb)   ((mb)->ol_flags & IND_ATTACHED_MBUF)
> >>>>> +#define RTE_MBUF_INDIRECT(mb)   RTE_MBUF_CLONED(mb)
> >>>> 
> >>>> It is still confusing that INDIRECT != !DIRECT.
> >>>> May be we have no good options right now, but I'd suggest to at least
> >>>> deprecate
> >>>> RTE_MBUF_INDIRECT() and completely remove it in the next release.
> >>> 
> >>> Agree. I may have missed something, but is my previous suggestion
> >>> not doable?
> >>> 
> >>> - direct = embeds its own data      (and indirect = !direct)
> >>> - clone (or another name) = data is another mbuf
> >>> - extbuf = data is in an external buffer
> >> 
> >> Any comment about this option?
> > 
> > I liked your idea, so I defined RTE_MBUF_CLONED() and wanted to deprecate
> > RTE_MBUF_INDIRECT() in the coming release. But RTE_MBUF_DIRECT() can't be
> > (!RTE_MBUF_INDIRECT()) because it will logically include RTE_MBUF_HAS_EXTBUF().
> > I'm not sure I understand you correctly.
> > 
> > Can you please give me more guidelines so that I can take you idea?
> 
> Maybe, did you mean the following? Looks like doable but RTE_MBUF_DIRECT()
> can't logically mean 'mbuf embeds its own data', right?
> 
> #define RTE_MBUF_INDIRECT(mb)   ((mb)->ol_flags & IND_ATTACHED_MBUF)
> #define RTE_MBUF_DIRECT(mb)     (!RTE_MBUF_INDIRECT(mb))
> 
> #define RTE_MBUF_HAS_EXTBUF(mb) ((mb)->ol_flags & EXT_ATTACHED_MBUF)
> #define RTE_MBUF_CLONED(mb)     ((mb)->ol_flags & IND_ATTACHED_MBUF)

I was thinking about something like this:

#define RTE_MBUF_HAS_EXTBUF(mb) ((mb)->ol_flags & EXT_ATTACHED_MBUF)
#define RTE_MBUF_CLONED(mb)     ((mb)->ol_flags & IND_ATTACHED_MBUF)

#define RTE_MBUF_DIRECT(mb)     (!RTE_MBUF_HAS_EXTBUF(mb) && !RTE_MBUF_CLONED(mb))
#define RTE_MBUF_INDIRECT(mb)   (!RTE_MBUF_DIRECT(mb))