Add gNOI Reboot HLD.

[github76543]

Initial draft of gNOI Reboot HLD.

[linux-foundation-easycla]

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• ✅ login: github76543 / name: John Hamrick (e470a36, 5ba899a)

[ganglyu]

Why do we need this backend daemon? Can we use GNOI server to invoke DBUS?

[github76543]

@bhagatgit
@akarshgupta

[akarshgupta25]

#1485 proposes daemonizing the warm-boot orchestration and thus will be the backend for warm-boot requests. Additionally, we want a common backend daemon for all types of reboots (cold, warm etc.). If we don't have this daemon then gNOI server would need to figure out the back-end based on the reboot request type. In my opinion, having a common backend provides a cleaner architecture, hence this backend daemon has been proposed.

[qiluo-msft]

system reboot

Could you detailed the reboot design for all the methods? There is no straightforward mapping between these methods with gNOI enum RebootMethod. We prposed below mapping:

enum RebootMethod {
  UNKNOWN = 0;     // Invalid default method.
  COLD = 1;        // Shutdown and restart OS and all hardware.
  POWERDOWN = 2;   // Halt and power down, if possible.
  HALT = 3;        // Halt, if possible.
  WARM = 4;        // Reload configuration but not underlying hardware.
  NSF = 5;         // Non-stop-forwarding reboot, if possible.
  // RESET method is deprecated in favor of the gNOI FactoryReset.Start().
  reserved 6;
  POWERUP = 7;     // Apply power, no-op if power is already on.
}

For SONiC cold reboot, we can use COLD method.
For SONiC warm reboot, we can use WARM method.
For SONiC fast reboot, we can use NSF method.
For SONiC config reload, we can use reserved method.

[github76543]

@akarshgupta
@bhagatgit

[akarshgupta25]

I am not sure why WARM and NSF reboot methods are defined separately in the gNOI spec. In my opinion they both refer to the same operation. I would propose adding a new reboot method for fast reboot since it doesn't map to any of the current gNOI reboot methods.