hesela.devMCTP message tag
An MCTP message tag is a three-bit transport field that identifies a message together with source endpoint and tag-owner context.
In a request/response exchange, the responder should return the request's tag with Tag Owner cleared. Packet sequence numbers are separate two-bit fields used within message assembly, not telemetry sample numbers. [1]
Linux supports explicit tag allocation and release for a peer. Zero is a valid tag value; the returned socket value also contains owner and preallocation flags. If a tag cannot be allocated for a send, the API reports EAGAIN. This is a collection-path error, not a decoded NVMe health warning. [2]
Collector design inference: keep an independent sample identifier, timestamp and device identity. Repeated tag values alone do not prove duplicate health samples or establish their chronological order.
Relations
- related
- Management Component Transport Protocol, MCTP endpoint ID, NVMe-MI, Out-of-band storage management
Citations
- DMTF DSP0236 v1.3.3, section 8.2 Table 1: message tag, Tag Owner and packet sequence
- Linux v6.12 MCTP socket documentation: send and tag allocation/release
Sources & caveats
- Source review of DSP0236 v1.3.3 and the Linux v6.12 documentation, not a hardware test. Collector identity advice is an inference from the scoped and reusable transport tag.