Make sure compiler_meta__->drop starts out false

[vbnogueira]

We found scenarios where the skb->cb is not zeroed out before the bpf
program is called. Since compiler_meta__ = skb->cb, there is an issue in
some specific scenarios. For example, since the bpf code looks at
compiler_meta__->drop to tell whether the packet should be dropped or not,
if by any chance compiler_meta__->drop is initialised to true, the
program will mistakenly drop the packet. To solve this, we are
initialising compiler_meta__->drop to false before doing any
processing on compiler_meta__->drop.

[vbnogueira]

@komaljai @Sosutha please take a look when you have some time

[vbnogueira]

@komaljai please take another look when you have some time

[vbnogueira]

@komaljai please take another look when you have some time

So, tested a bit more your suggestion, that is, initialising compiler_meta__->drop to false only when compiler_meta__->recirculated is false and there are cases where it doesn't work
Essentially because in such cases compiler_meta__->recirculated (its memory area in skb->cb) is also initialised with rubbish by the bpf program caller
So I had to revert the change and initialise compiler_meta__->drop to false unconditionally
Since I don't think a scenario where we recirculate with drop set makes much sense (since I believe we should just drop instead of recirculating in that case), I think initialising drop unconditionally should work fine

[komaljai]

I was referring to struct pna_pre_input_metadata_t->pass field in pna.p4 file. This will give the current pass number and if it is pass 1, then we should initialize the compiler_meta__->drop value to false.
In tc pna.p4 file, we should add PreControlT control block, similar to standard pna.p4 file.

[vbnogueira]

I was referring to struct pna_pre_input_metadata_t->pass field in pna.p4 file. This will give the current pass number and if it is pass 1, then we should initialize the compiler_meta__->drop value to false. In tc pna.p4 file, we should add PreControlT control block, similar to standard pna.p4 file.

I see, but if pna_pre_input_metadata_t->pass will come from skb->cb, as does compiler_meta__->recirculated, I believe it would suffer from the same issue (being initialised with rubbish)
That is, of course, if I am understanding this correctly
Also it seems like they removed PreControl from the PNA spec (as of version 0.7)

[Sosutha]

Looks fine

[fruffy]

Also it seems like they removed PreControl from the PNA spec (as of version 0.7)

This discussion on the customizations of pna.p4 flavors might be relevant. @jafingerhut Do you recall the reason why PreControl was removed?

[jafingerhut]

The reason that PreControl was introduced in the first place was during a long back-and-forth discussion (some of it between me at different times :-) on how to implement decryption in PNA in a way that hopefully multiple NICs could do, including the Intel IPU. Later around late 2022 or early 2023 we found a different way that does not require the PreControl, and seemed cleaner to everyone involved, so it was removed.

[komaljai]

@vbnogueira Could you rebase the PR?

[vbnogueira]

@vbnogueira Could you rebase the PR?

Done