Re: [dpdk-dev] [PATCH v6 1/9] librte_mbuf:the rte_mbuf structure changes

[Thomas Monjalon <thomas.monjalon@6wind.com>]

2014-11-12 14:31, Zhang, Helin:
> > 2014-10-23 02:23, Zhang, Helin:
> > > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Thomas Monjalon
> > > > 2014-10-21 14:14, Liu, Jijiang:
> > > > > From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
> > > > > > 2014-10-21 16:46, Jijiang Liu:
> > > > > > > +	uint16_t packet_type;
> > > > > >
> > > > > > Why not name it "l2_type"?
> > >
> > > 'packet_type' is for storing the hardware identified packet type upon
> > > different layers of protocols (l2, l3, l4, ...).
> > > It is quite useful for user application or middle layer software
> > > stacks, it can know what the packet type is without checking the packet too
> > much by software.
> > > Actually ixgbe already has packet types (less than 10), which is transcoded into
> > 'ol_flags'.
> > > For i40e, the packet type can represent about 256 types of packet,
> > > 'ol_flags' does not have enough bits for it anymore. So put the i40e packet
> > types into mbuf would be better.
> > > Also this field can be used for NON-Intel NICs, I think there must be
> > > the similar concepts of other NICs. And 16 bits 'packet_type' has severl
> > reserved bits for future and NON-Intel NICs.
> > 
> > Thanks Helin, that's the best description of packet_type I've seen so far.
> > It's not so clear in the commit log:
> > 	http://dpdk.org/browse/dpdk/commit/?id=73b7d59cf4f6faf
> > 
> > > > > In datasheet, this term is called packet type(s).
> > > >
> > > > That's exactly the point I want you really understand!
> > > > This is a field in generic mbuf structure, so your datasheet has no value here.
> > > >
> > > > > Personally , I think packet type is  more clear what meaning of this field is .
> > > >
> > > > You cannot add an API field without knowing what will be its generic meaning.
> > > > Please think about it and describe its scope.
> > 
> > I integrated this patch with the VXLAN patchset in the hope that you'll improve
> > the situation afterwards.
> > This is the answer you recently gave to Olivier:
> > 	http://dpdk.org/ml/archives/dev/2014-November/007599.html
> > "
> > 	Regarding adding a packet_type in mbuf, we ever had a lot of discussions as
> > follows:
> > 	http://dpdk.org/ml/archives/dev/2014-October/007027.html
> > 	http://dpdk.org/ml/archives/dev/2014-September/005240.html
> > 	http://dpdk.org/ml/archives/dev/2014-September/005241.html
> > 	http://dpdk.org/ml/archives/dev/2014-September/005274.html
> > "
> > 
> > To sum up the situation:
> > - We don't know what are the possible values of packet_type
> > - It's only filled by i40e, while other drivers use ol_flags
> > - There is no special value "unknown" which should be set by drivers
> >   not supporting this feature.
> > - Its only usage is to print a decimal value in app/test-pmd/rxonly.c
> 
> Though I haven't investigate this too much, my opinion is that we should
> use packet_type in the future, and rework igb/ixgbe PMD to remove all
> packet types in ol_flags and use packet_type instead.
> Then example app can use the packet type directly. And all igb, ixgbe and
> i40e packet_type are consistent. Sure we might need to define all packet
> types in rte_ethdev.h or similar header files.

Exact!

> > It's now clear that nobody cares about this part of the API.
> > So I'm going to remove packet_type from mbuf.
> > I don't want to keep something that we don't know how to use, that is not
> > consistent across drivers, and that overlap another API part (ol_flags).

Helin, I feel you perfectly understood the problem.
As the responsible of i40e, you can make a choice for 1.8 release:
- remove (incomplete) packet_type
- or complete it quickly

Thanks
-- 
Thomas