feat: store OTEL process context in named anonymous mapping on Linux #3937

nsavoire · 2025-09-01T21:28:53Z

What does this PR do?

This PR stores the tracer process level context in a named anonymous mapping on Linux.

PROF-12406

Motivation

Project plan

Datadog proposal to OTel
Technical RFC on process-level information and why we chose named anonymous mapping over memfd

Reviewer's Checklist

Changed code has unit tests for its functionality at or near 100% coverage.
System-Tests covering this feature have been added and enabled with the va.b.c-dev version tag.
There is a benchmark for any new code, or changes to existing code.
If this interacts with the agent in a new way, a system test has been added.
New code is free of linting errors. You can check this by running ./scripts/lint.sh locally.
Add an appropriate team label so this PR gets put in the right place for the release notes.
Non-trivial go.mod changes, e.g. adding new modules, are reviewed by @DataDog/dd-trace-go-guild.

Unsure? Have a question? Request a review!

pr-commenter · 2025-09-01T21:36:11Z

Benchmarks

Benchmark execution time: 2025-11-17 11:33:34

Comparing candidate commit 76e24fe in PR branch nsavoire/process_level_context with baseline commit bce309f in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 24 metrics, 0 unstable metrics.

ivoanjo

Left a couple of comments!

My go-foo is not very strong so definitely worth getting a pass from someone that's not pretending to know go as well ;)

ivoanjo · 2025-09-04T09:32:53Z

ddtrace/tracer/otelprocesscontext_msgp.go

Oh, this is cool! Much better than generating this by hand as we did in the C implementation ;)

internal/otelcontextmapping_linux.go

nsrip-dd

I've tested this with a simple Go program that just starts the APM tracer and then blocks forever. I've set DD_ENV, service name, and other config values, and then used Ivo's shell script to confirm that the memory mapping is there and has the expected contents.

Just left a few small comments.

nsrip-dd · 2025-09-03T17:05:17Z

ddtrace/tracer/otelprocesscontext.go

+	// https://opentelemetry.io/docs/specs/semconv/registry/attributes/service/#service-version
+	ServiceVersion string `msg:"service.version"`
+	// https://opentelemetry.io/docs/specs/semconv/registry/attributes/telemetry/#telemetry-sdk-language
+	TelemetrySdkLanguage string `msg:"telemetry.sdk.language"`


Really small nitpick: the Go custom is to capitalize acronyms, like TelemetrySDKLanguage

internal/otelcontextmapping_linux.go

felixge · 2025-09-04T19:59:07Z

ddtrace/tracer/tracer.go

 		log.Error("failed to store the configuration: %s", err.Error())
 	}
+
+	processContext := otelProcessContext{


Do we have a doc that explains why were are not using the Memfd solution for OpenTelemetry? IIRC we had some good reason, but I forgot what it was. We should probably link to that doc here.

https://datadoghq.atlassian.net/wiki/spaces/PROF/pages/4951344716/In+progress+Sharing+Process+Level+Information+between+SDKs+and+the+full+host+profiler

The main reasons were:

memfd_create syscall might be blocked by some seccomp profiles

it requires more syscalls / IO since all symlinks in /proc/<pid>/fd/ need to be resolved until datadog-tracer-info-<id> file is found

The "not inherited by fork" is also a nice bonus, and connects back to the discussions happening internally on the meaning of "runtime-id" -- the anonymous mapping mechanism, because it's not inherited by forks won't have any issues with stale information (such as a runtime-id) being carried from parent to child process.

internal/otelcontextmapping_linux.go

darccio · 2025-11-14T15:14:40Z

internal/otelcontextmapping_linux.go

+// Unless explicitly stated otherwise all files in this repository are licensed
+// under the Apache License Version 2.0.
+// This product includes software developed at Datadog (https://www.datadoghq.com/).
+// Copyright 2025 Datadog, Inc.
+
+//go:build linux


I know this is a Linux specific implementation, but it'd be good to have some tests. You can skip a test if the OS isn't Linux like this:

func TestCreateOtelProcessContextMapping(t *testing.T) { if runtime.GOOS != "linux" { t.Skip("OTEL process context mapping is only supported on Linux") } }

I was reluctant to add a test because of all the code needed to read the mapping.
But so be it, I added a test.

r1viollet · 2025-11-19T13:10:36Z

@darccio would you have time for this review ? 🙇

nsavoire requested review from a team as code owners September 1, 2025 21:28

nsavoire force-pushed the nsavoire/process_level_context branch from 0cd2733 to 99d1142 Compare September 1, 2025 21:32

nsavoire changed the title ~~[PROF-12406] feat: store OTEL process context in named anonymous mapping on Linux~~ feat: store OTEL process context in named anonymous mapping on Linux Sep 2, 2025

nsavoire force-pushed the nsavoire/process_level_context branch 2 times, most recently from f4348e8 to 56e26fa Compare September 2, 2025 08:08

ivoanjo reviewed Sep 4, 2025

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nsavoire requested a review from ivoanjo September 4, 2025 11:52

nsavoire force-pushed the nsavoire/process_level_context branch from 2282839 to 3025072 Compare September 4, 2025 12:12

nsrip-dd reviewed Sep 4, 2025

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felixge reviewed Sep 4, 2025

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jbachorik mentioned this pull request Sep 9, 2025

Add a PoC for OTel process context support DataDog/dd-trace-java#9472

Merged

nsavoire added 2 commits November 13, 2025 16:43

feat: store OTEL process context in named anonymous mapping on Linux

f705452

Address review comments

0111ebb

nsavoire force-pushed the nsavoire/process_level_context branch from d14c0bc to 0111ebb Compare November 14, 2025 14:46

nsavoire requested a review from a team as a code owner November 14, 2025 14:46

nsavoire requested a review from nsrip-dd November 14, 2025 14:50

Updated generated file

87f4825

nsrip-dd approved these changes Nov 14, 2025

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darccio requested changes Nov 14, 2025

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nsavoire requested a review from darccio November 14, 2025 21:19

Add tests

76e24fe

nsavoire force-pushed the nsavoire/process_level_context branch from e5bd886 to 76e24fe Compare November 17, 2025 11:02

feat: store OTEL process context in named anonymous mapping on Linux #3937

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feat: store OTEL process context in named anonymous mapping on Linux #3937

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r1viollet commented Nov 19, 2025

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nsavoire commented Sep 1, 2025 •

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