Sled Agent must be capable of inferring, communicating "own sled" version information

[smklein]

This is necessary for a few cases:

• Bootstrapping the rack. Before CRDB is populated and holding version information, the sled must be capable of self-reporting versioning information about underlying software components.
• Recovering a sled. If we move sleds between racks, manually modify a sled, etc, the sled should be able to provide an accounting of the "source of truth" of versioning information beyond what CRDB is capable of storing.

There are two major components to this issue:

• [ ] Sled Agent being able to infer component information
  • [ ] Given a zone image, the version should be embedded within it
  • [ ] Given a host OS image, the version should be acquirable (mechanism TBD)
  • [ ] Given Bootloaders / Hubris images local to the sled, the sled agent should be able to communicate with the local SP via UART to collect this information.
• [ ] Sled agent being able to propagate this information upward to Nexus

[rmustacc]

When sled agent is trying to gather information about itself, why should we assume MGS exists? If we want version info about ourselves isn't the only safe way to ask the local SP via the UART? This is mostly in the context of the " Given Bootloaders / Hubris images throughout the rack, the sled agent should be able to communicate over MGS to collect this information.".

[smklein]

When sled agent is trying to gather information about itself, why should we assume MGS exists? If we want version info about ourselves isn't the only safe way to ask the local SP via the UART? This is mostly in the context of the " Given Bootloaders / Hubris images throughout the rack, the sled agent should be able to communicate over MGS to collect this information.".

I've updated the issue to reflect this, especially for querying sled-local info.

For querying info that's "Rack-wide, but not sled local", such as "what's the version of Hubris running on the PSC", would MGS be an appropriate avenue?

[jgallagher]

For querying info that's "Rack-wide, but not sled local", such as "what's the version of Hubris running on the PSC", would MGS be an appropriate avenue?

MGS is the only avenue to ask questions of the PSC. MGS is arguably the right mechanism to interrogate the sidecar SP, too; although it has a couple side channels to talk to the scrimlet, none of these are as fit for this purpose as the uart is for a gimlet (I think?).

[rmustacc]

For querying info that's "Rack-wide, but not sled local", such as "what's the version of Hubris running on the PSC", would MGS be an appropriate avenue?

Yes, but it shouldn't be sled agent reaching out to MGS.