Grafana's log-level buttons filter on a field called `level`; no row in
the store has one. The store's name for it is `severity_text`, chosen by
VictoriaLogs' OTLP ingester rather than by us — v1.52.0's
`app/vlinsert/opentelemetry/pb.go` writes it unconditionally and the
ingest parameters have no `_level_field` to rename it with. So the
mapping is made on the reader: the VictoriaLogs datasource, which was
provisioned with no `jsonData` at all, now carries a `logLevelRules`
entry per severity the journald parser can emit.
`logLevelRules` is the datasource plugin's only level-related jsonData
key — there is no field-name setting and no OpenTelemetry preset to
switch on. It is read off `instanceSettings.jsonData` in the plugin's
`datasource.ts` and typed in its `configuration/LogLevelRules/types.ts`,
both recovered from the sourcemap shipped in the pinned artifact
(`grafanaPlugins.victoriametrics-logs-datasource` 0.26.3). Each enabled
rule appends an `OR severity_text:="INFO"`-shaped term to the query a
level button emits, next to the `level:…` term that matches nothing.
A wrong rule here fails silently: Grafana provisions unknown jsonData
without complaint and the buttons go on returning zero rows. The three
ways to get one wrong — a non-literal `enabled`, a non-canonical `level`
spelling, a value that is not the stored text — are recorded at the
binding, and a module-eval arm pins them along with the real failure
mode, a severity added to `nix/journald-severity.nix` and not here.
`Unspecified` is left unmapped on purpose: it is the store's own
rendering of an absent severity and the thing the logs dashboard's "no
severity" panel counts.
Refs #4560
8e9ca3ee6c