Hi Olivier

Hi Konstantin,

On 06/13/2016 06:31 PM, Ananyev, Konstantin wrote:

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Hi Olivier,

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Hi Konstantin,

On 06/13/2016 04:42 PM, Ananyev, Konstantin wrote:

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The behavior of PKT_RX_VLAN_PKT was not very well defined, resulting in
PMDs not advertising the same flags in similar conditions.

Following discussion in [1], introduce 2 new flags PKT_RX_VLAN_STRIPPED
and PKT_RX_QINQ_STRIPPED that are better defined:

   PKT_RX_VLAN_STRIPPED: a vlan has been stripped by the hardware and its
   tci is saved in mbuf->vlan_tci. This can only happen if vlan stripping
   is enabled in the RX configuration of the PMD.

For now, the old flag PKT_RX_VLAN_PKT is kept but marked as deprecated.
It should be removed from applications and PMDs in a future revision.

I am not sure it has to be deprecated & removed.
ixgbe (and igb as I can read the specs) devices can provide information is that
a vlan packet or not even when vlan stripping is disabled.
Right now ixgbe PMD do carry thins information to the user,
and I suppose igb could be improved to carry it too.
So obviously we need a way to pass that information to the upper layer.
I remember it was a discussion about introducing new packet_type
instead of ol_flag value PKT_RX_VLAN_PKT.
But right now it is not there, and again I don't know how easy it would be to replace
one with another without performance considering that packet_type is not supported
now by ixgbe vRX.
If we would be able to replace it, then yes we can deprecate and drop the   PKT_RX_VLAN_PKT.
But till then, I think we'd better keep it.

I think the packet_type feature would be more appropriate than a flag
for carrying this kind of info.

Currently the behavior of PKT_RX_VLAN_PKT is not properly defined,
and it is not the same on all PMDs. So, from an application
perspective, it's not usable except if it knows that the underlying
PMD is an ixgbe.

Yes, but it might be apps which do use that ixgbe functionality.

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This is not acceptable for a generic API and that's
why I think this flag, as it is today, should be deprecated.

I suppose we can't deprecate existing functionality without
providing working alternative.
I agree there is no proper way to know right now which device
supports it, which not, but to me it means we should add such ability,
not deprecate existing and (I believe) useful functionality.

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It won't prevent an application from using the flag right after my
commit, but it will warn the user that the flag should not be used
as is. If someone is willing to work on this feature for 16.11, why
not but again, I think using the packet_type is more appropriate.

I am not against providing that information via packet_type.
What I am saying:
1) right now it is not here.
2) it might not that easy in terms of performance.

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The problem is that I don't want to have this flag in this state
forever, and I also don't want to add in rte_mbuf.h a comment
saying "this flag does this on ixgbe and that on other drivers".

Then we need either:
- implement it as ptype
- add user ability to query is that flag is supported by the underlying device.

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If we decide to generalize the ixgbe behavior for all PMDs for this
flag, it will break the applications relying on this flag but with
other PMDs. So for the same reason we added a new PKT_RX_VLAN_STRIPPED
we cannot change the behavior of an existing flag.

Ok, then let's make PKT_RX_VLAN_STRIPPED == PKT_RX_VLAN,
and assign new value to the  PKT_RX_VLAN.
Or have PKT_RX_VLAN_STRIPPED == PKT_RX_VLAN and create a new one:
PKT_RX_VLAN_PRESENT or so.
?

I think adding this new flag/packet_type is a new feature,
because only ixgbe was behaving like this, and this was not
documented. To me, marking the old flag as deprecated is
a good compromise to keep the application relying on this
working. If you feel the term "deprecated" is not adapted,
we could reword it to something weaker.

Yes, that would do I think.
Basically my only concern that we will mark it as deprecated,
and then will remove it (as it is deprecated), without providing
anything new to replace it. 

We should try to not stay in that state too long,

Agree.

and anybody willing to implement this feature would be welcome. For my
part, this is not something I plan to do yet.

Ok, we'll see what we can do for 16.11.
But no hard promises right now either :)

Thanks
Konstantin

Regards,
Olivier