Re: [dpdk-dev] [PATCH v3 1/2] mbuf: support attaching external buffer to mbuf

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

Hi,

On Mon, Apr 23, 2018 at 06:29:57PM -0700, Yongseok Koh wrote:
> On Mon, Apr 23, 2018 at 06:18:43PM +0200, Olivier Matz wrote:
> > I'm a bit afraid about ABI breakage, we need to check that a
> > 18.02-compiled application still works well with this change.
> 
> I had the same concern so I made rte_pktmbuf_attach_extbuf() __rte_experimental.
> Although this new ol_flag is introduced, it can only be set by the new API and
> the rest of changes won't be effective unless this flag is set.
> RTE_MBUF_HAS_EXTBUF() will always be false if -DALLOW_EXPERIMENTAL_API isn't
> specified or rte_pktmbuf_attach_extbuf() isn't called. And there's no change
> needed in a C file. For this reason, I don't think there's ABI breakage.
> 
> Sounds correct?

Hmm, imagine you compile an application on top of 18.02.
Then, you update your dpdk libraries to 18.05.

The mlx driver may send mbufs pointing to an external buffer to the
application. When the application will call the mbuf free function, it
will probably not do the expected work, because most of the functions
involved are inline. So, to me this is an ABI breakage.

This is not a technical issue, since the ABI of mbuf will already be
broken this release (control mbuf removed). This is more a process
question, because an ABI breakage and its area should be announced.

Olivier