LDWG Meeting minutes: March 26, 2018

Attendees

• Antonin Bas (Barefoot)
• Mihai Budiu (VMware)
• Gordon Brebner (Xilinx)
• Calin Cascaval (Barefoot)
• James Coole (Cisco)
• Chris Dodd (Barefoot)
• Andy Fingerhut (Cisco)
• Nate Foster (Cornell)
• Yitzhak Gottlieb
• Vladimir Gurevich (Barefoot)
• Andy Keep (Cisco)
• Chris Sommers (Keysight)
• SK Sodhi (?)
• Yuki Hisata (One Net Systems)
• Milad Sharif (Barefoot)
• Han Wang (Barefoot)

Status Update and Announcements (Nate / Gordon)

Typedef Aliases

• PSA has 7 target-specific types---e.g., Portid_t
• But P4 Runtime wants to use a uniform type to manipulate these---e.g., bit<16>
• Goals:
  • Generate target-independent P4Info from myp4prog.p4
  • Generate target-specific compiled versions from myp4prog.p4 and psa.p4
• Proposals:
  • Add annotations to typedefs
  • Add newtype declaration
• Two issues:
  • Want capability to link different modules together
  • Want to expose/manipulate different types in data plane and control plane
• Action Item: Andy F to convene sub working group

Parser value sets

• Status update:

  • Size added as a constructor parameter
  • PR modifies the p4c IR to reflect this change

• Question: should we write “tuple” for the elements of the value set? Or “struct” so the control-plane API becomes simpler?

• Action Item: Han to incorporate improvements from offline discussion into PR; we’ll finalize next time.

Table "size" and reserved annotations

• See also notes from Andy F.
• Proposal: add size as a standard, but optional attribute of tables
• Challenge: size is difficult to talk about on hardware targets due to complex encodings of patterns.
• Proposal: meaning is that compiler must reserve space for at least N entries, but doesn’t necessarily mean that adding N entries will succeed.
• Action Item: Andy F to create PR with link to notes.

Documentation

• API WG has proposed adding top-level metadata to the program through annotations.
• Desire to standardize the structure of these annocations, which would appear at the start of the document.
• Question: should we provide special annotation syntax for key-value pairs? Action Item: Chris to refine proposal and discuss with Mihai on syntactic improvements

Serializable Types

• Andy K has produced a document summarizing the design Link to Andy K’s PDF.
• Questions:
  • How to ensure type safety with enums and non-contiguous values? Action Item: Andy K to lead sub-working group

Saturating Fields

• Tradeoffs between adding a new type and a new operation.
• Action Item: Calin to address lingering issues through offline discussion, and create PR.

Announcements

• Next meeting: April 16th @ Barefoot