fix(library-config): update Linux process context

[cataphract]

What does this PR do?

This is 2/3 in the stacked process-context series and depends on #2228.

It adapts the Linux implementation after the code-organization layer:

• makes MADV_DONTFORK best-effort instead of treating it as a publishing failure;
• detects whether the process-context mapping is available after a fork, rather than relying on a stored publisher PID;
• avoids reading or unmapping inherited state when the mapping is not present in the child;
• updates the Unix copy-pipe implementation and comments to match the current behavior;
• changes the default feature set to the writer, while keeping the reader available as an opt-in feature.

Why?

#2228 intentionally preserves the old Linux behavior while introducing the shared reader/writer structure. This PR applies the Linux behavior changes separately so they can be reviewed without being mixed with either the file reorganization or the macOS/Windows implementation.

Impact

Linux keeps the same platform-agnostic process-context API, with corrected fork handling and the final feature defaults. This layer does not add macOS or Windows support.

Validation

Validated independently at this commit with:

• cargo check -p libdd-library-config --all-features;
• cargo check -p libdd-library-config-ffi;
• cargo nextest run -p libdd-library-config --all-features --no-fail-fast;
• cargo nextest run -p libdd-library-config --no-default-features --features process-context-reader --no-fail-fast.

Stack

1. refactor(library-config): reorganize Linux process context #2228 — reorganize the Linux process context
2. fix(library-config): update Linux process context #2237 — update the Linux implementation
3. feat(library-config): add macOS and Windows process context #2238 — add macOS and Windows support

[github-actions]

📚 Documentation Check Results

⚠️ 265 documentation warning(s) found

📦 libdd-library-config - 265 warning(s)

---

Updated: 2026-07-14 23:07:23 UTC | Commit: 64ca9ca | missing-docs job results

[github-actions]

🔒 Cargo Deny Results

⚠️ 1 issue(s) found, showing only errors (advisories, bans, sources)

📦 libdd-library-config - 1 error(s)

Show output

error[unsound]: Rand is unsound with a custom logger using `rand::rng()`
   ┌─ /home/runner/work/libdatadog/libdatadog/Cargo.lock:46:1
   │
46 │ rand 0.8.5 registry+https://github.com/rust-lang/crates.io-index
   │ ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ unsound advisory detected
   │
   ├ ID: RUSTSEC-2026-0097
   ├ Advisory: https://rustsec.org/advisories/RUSTSEC-2026-0097
   ├ It has been reported (by @lopopolo) that the `rand` library is [unsound](https://rust-lang.github.io/unsafe-code-guidelines/glossary.html#soundness-of-code--of-a-library) (i.e. that safe code using the public API can cause Undefined Behaviour) when all the following conditions are met:
     
     - The `log` and `thread_rng` features are enabled
     - A [custom logger](https://docs.rs/log/latest/log/#implementing-a-logger) is defined
     - The custom logger accesses `rand::rng()` (previously `rand::thread_rng()`) and calls any `TryRng` (previously `RngCore`) methods on `ThreadRng`
     - The `ThreadRng` (attempts to) reseed while called from the custom logger (this happens every 64 kB of generated data)
     - Trace-level logging is enabled or warn-level logging is enabled and the random source (the `getrandom` crate) is unable to provide a new seed
     
     `TryRng` (previously `RngCore`) methods for `ThreadRng` use `unsafe` code to cast `*mut BlockRng<ReseedingCore>` to `&mut BlockRng<ReseedingCore>`. When all the above conditions are met this results in an aliased mutable reference, violating the Stacked Borrows rules. Miri is able to detect this violation in sample code. Since construction of [aliased mutable references is Undefined Behaviour](https://doc.rust-lang.org/stable/nomicon/references.html), the behaviour of optimized builds is hard to predict.
   ├ Announcement: https://github.com/rust-random/rand/pull/1763
   ├ Solution: Upgrade to >=0.10.1 OR <0.10.0, >=0.9.3 OR <0.9.0, >=0.8.6 (try `cargo update -p rand`)
   ├ rand v0.8.5
     └── libdd-library-config v3.0.0

advisories FAILED, bans ok, sources ok

---

Updated: 2026-07-14 23:09:17 UTC | Commit: 64ca9ca | dependency-check job results

[pr-commenter]

Benchmarks

Comparison

Candidate

Candidate benchmark details

Baseline

Baseline benchmark details

[datadog-datadog-prod-us1]

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 80.26%
• Overall Coverage: 74.47% (-0.03%)

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 97138bc | Docs | Datadog PR Page | Give us feedback!}

[dd-octo-sts]

Artifact Size Benchmark Report

aarch64-alpine-linux-musl

Artifact	Baseline	Commit	Change
/aarch64-alpine-linux-musl/lib/libdatadog_profiling.so	7.88 MB	7.88 MB	0% (0 B) 👌
/aarch64-alpine-linux-musl/lib/libdatadog_profiling.a	86.15 MB	86.16 MB	+.01% (+9.55 KB) 🔍

aarch64-unknown-linux-gnu

Artifact	Baseline	Commit	Change
/aarch64-unknown-linux-gnu/lib/libdatadog_profiling.a	97.40 MB	97.41 MB	+.01% (+10.98 KB) 🔍
/aarch64-unknown-linux-gnu/lib/libdatadog_profiling.so	10.62 MB	10.62 MB	+0% (+88 B) 👌

libdatadog-x64-windows

Artifact	Baseline	Commit	Change
/libdatadog-x64-windows/debug/dynamic/datadog_profiling_ffi.dll	25.54 MB	25.54 MB	0% (0 B) 👌
/libdatadog-x64-windows/debug/dynamic/datadog_profiling_ffi.lib	88.44 KB	88.44 KB	0% (0 B) 👌
/libdatadog-x64-windows/debug/dynamic/datadog_profiling_ffi.pdb	185.33 MB	185.34 MB	+0% (+16.00 KB) 👌
/libdatadog-x64-windows/debug/static/datadog_profiling_ffi.lib	957.25 MB	957.26 MB	+0% (+10.35 KB) 👌
/libdatadog-x64-windows/release/dynamic/datadog_profiling_ffi.dll	8.35 MB	8.35 MB	0% (0 B) 👌
/libdatadog-x64-windows/release/dynamic/datadog_profiling_ffi.lib	88.44 KB	88.44 KB	0% (0 B) 👌
/libdatadog-x64-windows/release/dynamic/datadog_profiling_ffi.pdb	24.72 MB	24.72 MB	0% (0 B) 👌
/libdatadog-x64-windows/release/static/datadog_profiling_ffi.lib	49.21 MB	49.21 MB	-0% (-228 B) 👌

libdatadog-x86-windows

Artifact	Baseline	Commit	Change
/libdatadog-x86-windows/debug/dynamic/datadog_profiling_ffi.dll	22.19 MB	22.19 MB	-0% (-512 B) 👌
/libdatadog-x86-windows/debug/dynamic/datadog_profiling_ffi.lib	89.82 KB	89.82 KB	0% (0 B) 👌
/libdatadog-x86-windows/debug/dynamic/datadog_profiling_ffi.pdb	189.78 MB	189.77 MB	-0% (-8.00 KB) 👌
/libdatadog-x86-windows/debug/static/datadog_profiling_ffi.lib	945.93 MB	945.94 MB	+0% (+10.35 KB) 👌
/libdatadog-x86-windows/release/dynamic/datadog_profiling_ffi.dll	6.46 MB	6.46 MB	0% (0 B) 👌
/libdatadog-x86-windows/release/dynamic/datadog_profiling_ffi.lib	89.82 KB	89.82 KB	0% (0 B) 👌
/libdatadog-x86-windows/release/dynamic/datadog_profiling_ffi.pdb	26.54 MB	26.54 MB	0% (0 B) 👌
/libdatadog-x86-windows/release/static/datadog_profiling_ffi.lib	46.82 MB	46.82 MB	-0% (-200 B) 👌

x86_64-alpine-linux-musl

Artifact	Baseline	Commit	Change
/x86_64-alpine-linux-musl/lib/libdatadog_profiling.a	76.96 MB	76.97 MB	+0% (+5.83 KB) 👌
/x86_64-alpine-linux-musl/lib/libdatadog_profiling.so	8.81 MB	8.81 MB	0% (0 B) 👌

x86_64-unknown-linux-gnu

Artifact	Baseline	Commit	Change
/x86_64-unknown-linux-gnu/lib/libdatadog_profiling.a	92.37 MB	92.38 MB	+0% (+5.37 KB) 👌
/x86_64-unknown-linux-gnu/lib/libdatadog_profiling.so	10.72 MB	10.72 MB	+.03% (+3.79 KB) 🔍