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LDWG meeting minutes, April 1, 2019

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Nate Foster edited this page Apr 1, 2019 · 2 revisions

Attendees

Mario Baldi (Cisco) Mihai Budiu (VMware) Chris Dodd (Barefoot) Andy Fingerhut (Cisco) Nate Foster (Cornell) Jed Liu (Barefoot) Antonin Bas (Barefoot) Han Wang (Barefoot)

Invalid Parser Arguments

Clarify semantics of order of const table entries

  • Pull Request: https://github.com/p4lang/p4-spec/pull/743
  • Proposal is to clarify notion of priority for const entries
  • Discussion focused on whether to define the semantics in a general way, or specifically in terms of `ternary.
  • Action item: rewrite text to be more general.

Allow emit and extract on arbitrary structs

  • Pull Request: https://github.com/p4lang/p4-spec/pull/736
  • Proposal is a record of an off-line discussion between @hanw and @jafingerhut
  • There are several open questions, such as what are restrictions on struct and how lookahead should work.
  • Perhaps there should be other kinds of packet_in and packet_out objects to handle these use cases?
  • This feature may not be needed; it was developed in preparation for minSizeInBits proposal.
  • Action Item: We'll let this sit until there is a compelling use case.

Static Header Size Operations

** Pull Request:** https://github.com/p4lang/p4-spec/pull/736

  • Only change since last discussion is to add min before names minSizeInBits and minSizeInBytes
  • In particular, max operations are not supported; if someone has a compelling use case, they can develop it.
  • Action Item: Merge into the spec

Translation from P4_14 to P4_16

  • Issue: https://github.com/p4lang/p4-spec/pull/1694
  • Pull Request: https://github.com/p4lang/p4c/pull/1704
  • Issue stems from the converter, which converted intrinsic metadata into user metadata, and hence Bmv2 couldn't find it.
  • Another way to view the issue is that compilation is not idempotent
  • The fix maps intrinsic metadata to standard metadata
  • @hanw wants to check that this would not have impact on a proprietary compiler
  • Also don't want to lose switch.p4 as a test case for the compiler
  • Action Item: More work to do. We will revisit.

Recirculate in V1Model

  • Internet connection in Germany cut...

Overlays

  • Pull Request: https://github.com/p4lang/p4-spec/pull/656
  • Proposal is to allow overlays, which give a different view of underlying state
  • Mihai would like this feature to be purely syntactic sugar
  • We believe that the current proposal, with overlays initialized just once, satisfies this property.
  • We want to make sure that overlays do not make it easy to write programs that do too much copying.
  • Action Items:
    • @mbudiu-vmw will continue to push forward with the overlay proposal
    • @antoninbas and @hanw will explore struct-based approach to their hash example

Next Meeting

  • We'll meet next Monday, April 8th.
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