From 9ce162f4411481369ecfa21c4591b6d1570dde83 Mon Sep 17 00:00:00 2001
From: "datadog-datadog-prod-us1[bot]"
 <88084959+datadog-datadog-prod-us1[bot]@users.noreply.github.com>
Date: Wed, 14 Jan 2026 21:24:26 +0000
Subject: [PATCH 1/4] Extract observer into new crate

Co-authored-by: scottopell <996472+scottopell@users.noreply.github.com>
---
 Cargo.toml                                    |  5 +++
 lading/Cargo.toml                             |  8 ++--
 lading/src/lib.rs                             |  3 +-
 lading/src/observer/linux/utils.rs            |  1 -
 lading_observer/Cargo.toml                    | 33 +++++++++++++++
 .../observer.rs => lading_observer/src/lib.rs | 41 ++++++++++---------
 .../observer => lading_observer/src}/linux.rs |  2 +-
 .../src}/linux/cgroup.rs                      |  0
 .../src}/linux/cgroup/v2.rs                   |  0
 .../src}/linux/cgroup/v2/cpu.rs               |  0
 .../src}/linux/cgroup/v2/io.rs                |  0
 .../src}/linux/cgroup/v2/memory.rs            |  0
 .../src}/linux/procfs.rs                      |  2 +-
 .../src}/linux/procfs/memory.rs               |  0
 .../src}/linux/procfs/memory/smaps.rs         |  2 +-
 .../src}/linux/procfs/memory/smaps_rollup.rs  |  0
 .../src}/linux/procfs/stat.rs                 |  2 +-
 .../src}/linux/procfs/uptime.rs               |  0
 .../src}/linux/procfs/vmstat.rs               |  0
 lading_observer/src/linux/utils.rs            |  1 +
 .../src}/linux/utils/process_descendents.rs   |  6 +--
 .../linux/utils/tests/create_process_tree.py  |  0
 .../src}/linux/wss.rs                         |  2 +-
 .../src}/linux/wss/pfnset.rs                  |  0
 24 files changed, 74 insertions(+), 34 deletions(-)
 delete mode 100644 lading/src/observer/linux/utils.rs
 create mode 100644 lading_observer/Cargo.toml
 rename lading/src/observer.rs => lading_observer/src/lib.rs (78%)
 rename {lading/src/observer => lading_observer/src}/linux.rs (98%)
 rename {lading/src/observer => lading_observer/src}/linux/cgroup.rs (100%)
 rename {lading/src/observer => lading_observer/src}/linux/cgroup/v2.rs (100%)
 rename {lading/src/observer => lading_observer/src}/linux/cgroup/v2/cpu.rs (100%)
 rename {lading/src/observer => lading_observer/src}/linux/cgroup/v2/io.rs (100%)
 rename {lading/src/observer => lading_observer/src}/linux/cgroup/v2/memory.rs (100%)
 rename {lading/src/observer => lading_observer/src}/linux/procfs.rs (99%)
 rename {lading/src/observer => lading_observer/src}/linux/procfs/memory.rs (100%)
 rename {lading/src/observer => lading_observer/src}/linux/procfs/memory/smaps.rs (99%)
 rename {lading/src/observer => lading_observer/src}/linux/procfs/memory/smaps_rollup.rs (100%)
 rename {lading/src/observer => lading_observer/src}/linux/procfs/stat.rs (99%)
 rename {lading/src/observer => lading_observer/src}/linux/procfs/uptime.rs (100%)
 rename {lading/src/observer => lading_observer/src}/linux/procfs/vmstat.rs (100%)
 create mode 100644 lading_observer/src/linux/utils.rs
 rename {lading/src/observer => lading_observer/src}/linux/utils/process_descendents.rs (93%)
 rename {lading/src/observer => lading_observer/src}/linux/utils/tests/create_process_tree.py (100%)
 mode change 100755 => 100644
 rename {lading/src/observer => lading_observer/src}/linux/wss.rs (97%)
 rename {lading/src/observer => lading_observer/src}/linux/wss/pfnset.rs (100%)

diff --git a/Cargo.toml b/Cargo.toml
index 634792332..a345747dd 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -8,6 +8,7 @@ members = [
   "lading_capture",
   "lading_fuzz",
   "lading_payload",
+  "lading_observer",
   "lading_throttle",
 ]
 
@@ -60,6 +61,10 @@ http-body-util = { version = "0.1" }
 http-serde = { version = "2.1" }
 hyper = { version = "1.7", default-features = false }
 hyper-util = { version = "0.1", default-features = false }
+heck = { version = "0.5", default-features = false }
+nix = { version = "0.30" }
+num-traits = { version = "0.2", default-features = false }
+regex = { version = "1.12" }
 sysinfo = { version = "0.37", default-features = false }
 opentelemetry-proto = "0.31"
 ddsketch-agent = { git = "https://github.com/DataDog/saluki", rev = "f47a7ef588c53aa1da35dcfd93808595ebeb1291", features = [
diff --git a/lading/Cargo.toml b/lading/Cargo.toml
index a53e1ea31..32ca72a1b 100644
--- a/lading/Cargo.toml
+++ b/lading/Cargo.toml
@@ -18,6 +18,7 @@ description = "A tool for load testing daemons."
 lading-capture = { version = "0.2", path = "../lading_capture" }
 lading-capture-schema = { path = "../lading_capture_schema" }
 lading-payload = { version = "0.1", path = "../lading_payload" }
+lading-observer = { version = "0.1", path = "../lading_observer" }
 lading-throttle = { version = "0.1", path = "../lading_throttle" }
 lading-signal = { version = "0.1", path = "../lading_signal" }
 
@@ -39,7 +40,6 @@ either = { version = "1.15.0" }
 flate2 = { version = "1.1.2" }
 futures = { version = "0.3.31" }
 fuser = { version = "0.16", optional = true, features = ["libfuse"] }
-heck = { version = "0.5", default-features = false }
 http = { workspace = true }
 http-body-util = { workspace = true }
 http-serde = { version = "2.1" }
@@ -53,14 +53,13 @@ k8s-openapi = { version = "0.26.0", default-features = false, features = [
 metrics = { workspace = true }
 metrics-exporter-prometheus = { workspace = true }
 metrics-util = { workspace = true }
-nix = { version = "0.30", features = ["fs", "signal"] }
+nix = { workspace = true, features = ["fs", "signal"] }
 num_cpus = { version = "1.17" }
-num-traits = { version = "0.2", default-features = false }
 once_cell = { workspace = true }
 opentelemetry-proto = { workspace = true }
 prost = { workspace = true }
 rand = { workspace = true, features = ["small_rng", "thread_rng"] }
-regex = { version = "1.12" }
+regex = { workspace = true }
 reqwest = { version = "0.12", default-features = false, features = [
   "default-tls",
   "json",
@@ -95,7 +94,6 @@ tracing-subscriber = { workspace = true, features = ["env-filter", "json"] }
 zstd = { version = "0.13.3" }
 
 [target.'cfg(target_os = "linux")'.dependencies]
-procfs = { version = "0.18", default-features = false, features = [] }
 async-pidfd = { version = "0.1" }
 
 [dev-dependencies]
diff --git a/lading/src/lib.rs b/lading/src/lib.rs
index f8d382aab..a4952fb82 100644
--- a/lading/src/lib.rs
+++ b/lading/src/lib.rs
@@ -17,7 +17,8 @@ mod common;
 pub mod config;
 pub mod generator;
 pub mod inspector;
-pub mod observer;
+/// Target observation utilities.
+pub use lading_observer as observer;
 pub(crate) mod proto;
 pub mod target;
 pub mod target_metrics;
diff --git a/lading/src/observer/linux/utils.rs b/lading/src/observer/linux/utils.rs
deleted file mode 100644
index 836f25422..000000000
--- a/lading/src/observer/linux/utils.rs
+++ /dev/null
@@ -1 +0,0 @@
-pub(in crate::observer::linux) mod process_descendents;
diff --git a/lading_observer/Cargo.toml b/lading_observer/Cargo.toml
new file mode 100644
index 000000000..07e4b3624
--- /dev/null
+++ b/lading_observer/Cargo.toml
@@ -0,0 +1,33 @@
+[package]
+name = "lading-observer"
+version = "0.1.0"
+authors = [
+  "Brian L. Troutwine <brian.troutwine@datadoghq.com>",
+  "George Hahn <george.hahn@datadoghq.com>",
+]
+edition = "2024"
+license = "MIT"
+repository = "https://github.com/datadog/lading/"
+keywords = ["random_test", "generator"]
+categories = ["development-tools::profiling"]
+description = "A tool for load testing daemons."
+
+[dependencies]
+lading-signal = { version = "0.1", path = "../lading_signal" }
+metrics = { workspace = true }
+nix = { workspace = true, features = ["fs", "signal"] }
+num-traits = { workspace = true }
+procfs = { version = "0.18", default-features = false, features = [] }
+regex = { workspace = true }
+rustc-hash = { workspace = true }
+serde = { workspace = true }
+thiserror = { workspace = true }
+tokio = { workspace = true, features = ["fs", "macros", "sync", "time"] }
+tracing = { workspace = true }
+heck = { workspace = true }
+
+[lib]
+doctest = false
+
+[lints]
+workspace = true
\ No newline at end of file
diff --git a/lading/src/observer.rs b/lading_observer/src/lib.rs
similarity index 78%
rename from lading/src/observer.rs
rename to lading_observer/src/lib.rs
index 6d1f3495f..da3fdea56 100644
--- a/lading/src/observer.rs
+++ b/lading_observer/src/lib.rs
@@ -1,21 +1,26 @@
-//! Manage the target observer
+//! Observe target resource usage for lading.
 //!
-//! The interogation that lading does of the target sub-process is intentionally
-//! limited to in-process concerns, for the most part. The 'inspector' does
-//! allow for a sub-process to do out-of-band inspection of the target but
-//! cannot incorporate whatever it's doing into the capture data that lading
-//! produces. This observer, on Linux, looks up the target process in procfs and
-//! writes out key details about memory and CPU consumption into the capture
-//! data. On non-Linux systems the observer, if enabled, will emit a warning.
+//! This library supports the lading binary found elsewhere in this project. It
+//! samples target resource usage, primarily on Linux via procfs, and is not
+//! intended for external use.
 
-use std::io;
+#![deny(clippy::cargo)]
+#![allow(clippy::cast_precision_loss)]
+#![allow(clippy::multiple_crate_versions)]
 
-use crate::target::TargetPidReceiver;
+use std::{io, time::Duration};
+
+#[cfg(target_os = "linux")]
+use crate::linux::Sampler;
 use serde::Deserialize;
+use tokio::sync::broadcast;
 
 #[cfg(target_os = "linux")]
 mod linux;
 
+/// Type used to receive the target PID once it is running.
+pub type TargetPidReceiver = broadcast::Receiver<Option<i32>>;
+
 #[derive(thiserror::Error, Debug)]
 /// Errors produced by [`Server`]
 pub enum Error {
@@ -38,13 +43,13 @@ pub enum Error {
 pub struct Config {}
 
 #[derive(Debug)]
-/// The inspector sub-process server.
+/// The observer sub-process server.
 ///
 /// This struct manages a sub-process that can be used to do further examination
-/// of the [`crate::target::Server`] by means of operating system facilities. The
-/// sub-process is not created until [`Server::run`] is called. It is assumed
-/// that only one instance of this struct will ever exist at a time, although
-/// there are no protections for that.
+/// of a target process by means of operating system facilities. The sub-process
+/// is not created until [`Server::run`] is called. It is assumed that only one
+/// instance of this struct will ever exist at a time, although there are no
+/// protections for that.
 pub struct Server {
     #[allow(dead_code)] // config is not actively used, left as a stub
     config: Config,
@@ -93,10 +98,8 @@ impl Server {
     pub async fn run(
         self,
         mut pid_snd: TargetPidReceiver,
-        sample_period: std::time::Duration,
+        sample_period: Duration,
     ) -> Result<(), Error> {
-        use crate::observer::linux::Sampler;
-
         let target_pid = pid_snd
             .recv()
             .await
@@ -143,7 +146,7 @@ impl Server {
     pub async fn run(
         self,
         _pid_snd: TargetPidReceiver,
-        _sample_period: std::time::Duration,
+        _sample_period: Duration,
     ) -> Result<(), Error> {
         tracing::warn!("observer unavailable on non-Linux system");
         Ok(())
diff --git a/lading/src/observer/linux.rs b/lading_observer/src/linux.rs
similarity index 98%
rename from lading/src/observer/linux.rs
rename to lading_observer/src/linux.rs
index 78dc5826f..5b1347a1c 100644
--- a/lading/src/observer/linux.rs
+++ b/lading_observer/src/linux.rs
@@ -3,7 +3,7 @@ mod procfs;
 mod utils;
 mod wss;
 
-use tracing::{error, warn};
+use tracing::warn;
 
 #[derive(thiserror::Error, Debug)]
 /// Errors produced by functions in this module
diff --git a/lading/src/observer/linux/cgroup.rs b/lading_observer/src/linux/cgroup.rs
similarity index 100%
rename from lading/src/observer/linux/cgroup.rs
rename to lading_observer/src/linux/cgroup.rs
diff --git a/lading/src/observer/linux/cgroup/v2.rs b/lading_observer/src/linux/cgroup/v2.rs
similarity index 100%
rename from lading/src/observer/linux/cgroup/v2.rs
rename to lading_observer/src/linux/cgroup/v2.rs
diff --git a/lading/src/observer/linux/cgroup/v2/cpu.rs b/lading_observer/src/linux/cgroup/v2/cpu.rs
similarity index 100%
rename from lading/src/observer/linux/cgroup/v2/cpu.rs
rename to lading_observer/src/linux/cgroup/v2/cpu.rs
diff --git a/lading/src/observer/linux/cgroup/v2/io.rs b/lading_observer/src/linux/cgroup/v2/io.rs
similarity index 100%
rename from lading/src/observer/linux/cgroup/v2/io.rs
rename to lading_observer/src/linux/cgroup/v2/io.rs
diff --git a/lading/src/observer/linux/cgroup/v2/memory.rs b/lading_observer/src/linux/cgroup/v2/memory.rs
similarity index 100%
rename from lading/src/observer/linux/cgroup/v2/memory.rs
rename to lading_observer/src/linux/cgroup/v2/memory.rs
diff --git a/lading/src/observer/linux/procfs.rs b/lading_observer/src/linux/procfs.rs
similarity index 99%
rename from lading/src/observer/linux/procfs.rs
rename to lading_observer/src/linux/procfs.rs
index dabc1f87c..5cbe7c4c1 100644
--- a/lading/src/observer/linux/procfs.rs
+++ b/lading_observer/src/linux/procfs.rs
@@ -14,7 +14,7 @@ use procfs::process::Process;
 use rustc_hash::FxHashMap;
 use tracing::{error, warn};
 
-use crate::observer::linux::utils::process_descendents::ProcessDescendantsIterator;
+use crate::linux::utils::process_descendents::ProcessDescendantsIterator;
 
 const BYTES_PER_KIBIBYTE: u64 = 1024;
 
diff --git a/lading/src/observer/linux/procfs/memory.rs b/lading_observer/src/linux/procfs/memory.rs
similarity index 100%
rename from lading/src/observer/linux/procfs/memory.rs
rename to lading_observer/src/linux/procfs/memory.rs
diff --git a/lading/src/observer/linux/procfs/memory/smaps.rs b/lading_observer/src/linux/procfs/memory/smaps.rs
similarity index 99%
rename from lading/src/observer/linux/procfs/memory/smaps.rs
rename to lading_observer/src/linux/procfs/memory/smaps.rs
index b8fd18a58..689d7738e 100644
--- a/lading/src/observer/linux/procfs/memory/smaps.rs
+++ b/lading_observer/src/linux/procfs/memory/smaps.rs
@@ -3,7 +3,7 @@ use std::{fs, io::Read};
 use regex::Regex;
 use rustc_hash::FxHashMap;
 
-use crate::observer::linux::procfs::BYTES_PER_KIBIBYTE;
+use crate::linux::procfs::BYTES_PER_KIBIBYTE;
 
 use super::next_token;
 
diff --git a/lading/src/observer/linux/procfs/memory/smaps_rollup.rs b/lading_observer/src/linux/procfs/memory/smaps_rollup.rs
similarity index 100%
rename from lading/src/observer/linux/procfs/memory/smaps_rollup.rs
rename to lading_observer/src/linux/procfs/memory/smaps_rollup.rs
diff --git a/lading/src/observer/linux/procfs/stat.rs b/lading_observer/src/linux/procfs/stat.rs
similarity index 99%
rename from lading/src/observer/linux/procfs/stat.rs
rename to lading_observer/src/linux/procfs/stat.rs
index ad85813c7..f06913c5a 100644
--- a/lading/src/observer/linux/procfs/stat.rs
+++ b/lading_observer/src/linux/procfs/stat.rs
@@ -1,7 +1,7 @@
 use metrics::gauge;
 use tokio::fs;
 
-use crate::observer::linux::cgroup;
+use crate::linux::cgroup;
 
 #[derive(thiserror::Error, Debug)]
 pub enum Error {
diff --git a/lading/src/observer/linux/procfs/uptime.rs b/lading_observer/src/linux/procfs/uptime.rs
similarity index 100%
rename from lading/src/observer/linux/procfs/uptime.rs
rename to lading_observer/src/linux/procfs/uptime.rs
diff --git a/lading/src/observer/linux/procfs/vmstat.rs b/lading_observer/src/linux/procfs/vmstat.rs
similarity index 100%
rename from lading/src/observer/linux/procfs/vmstat.rs
rename to lading_observer/src/linux/procfs/vmstat.rs
diff --git a/lading_observer/src/linux/utils.rs b/lading_observer/src/linux/utils.rs
new file mode 100644
index 000000000..8dc781208
--- /dev/null
+++ b/lading_observer/src/linux/utils.rs
@@ -0,0 +1 @@
+pub(in crate::linux) mod process_descendents;
diff --git a/lading/src/observer/linux/utils/process_descendents.rs b/lading_observer/src/linux/utils/process_descendents.rs
similarity index 93%
rename from lading/src/observer/linux/utils/process_descendents.rs
rename to lading_observer/src/linux/utils/process_descendents.rs
index a08a80dc9..9507f40f7 100644
--- a/lading/src/observer/linux/utils/process_descendents.rs
+++ b/lading_observer/src/linux/utils/process_descendents.rs
@@ -1,12 +1,12 @@
 use procfs::process::Process;
 
 /// Iterator which, given a process ID, returns the process and all its descendants
-pub(in crate::observer::linux) struct ProcessDescendantsIterator {
+pub(in crate::linux) struct ProcessDescendantsIterator {
     stack: Vec<Process>,
 }
 
 impl ProcessDescendantsIterator {
-    pub(in crate::observer::linux) fn new(parent_pid: i32) -> Self {
+    pub(in crate::linux) fn new(parent_pid: i32) -> Self {
         Self {
             stack: vec![
                 Process::new(parent_pid)
@@ -59,7 +59,7 @@ mod tests {
         const NB_PROCESSES: usize =
             (NB_PROCESSES_PER_LEVEL.pow(NB_LEVELS + 1) - 1) / (NB_PROCESSES_PER_LEVEL - 1);
 
-        let mut child = Command::new("src/observer/linux/utils/tests/create_process_tree.py")
+        let mut child = Command::new("src/linux/utils/tests/create_process_tree.py")
             .arg(NB_PROCESSES_PER_LEVEL.to_string())
             .arg(NB_LEVELS.to_string())
             .stdout(Stdio::piped())
diff --git a/lading/src/observer/linux/utils/tests/create_process_tree.py b/lading_observer/src/linux/utils/tests/create_process_tree.py
old mode 100755
new mode 100644
similarity index 100%
rename from lading/src/observer/linux/utils/tests/create_process_tree.py
rename to lading_observer/src/linux/utils/tests/create_process_tree.py
diff --git a/lading/src/observer/linux/wss.rs b/lading_observer/src/linux/wss.rs
similarity index 97%
rename from lading/src/observer/linux/wss.rs
rename to lading_observer/src/linux/wss.rs
index 4a3ba3795..096ae69d0 100644
--- a/lading/src/observer/linux/wss.rs
+++ b/lading_observer/src/linux/wss.rs
@@ -7,7 +7,7 @@ use std::{
 };
 use tracing::debug;
 
-use crate::observer::linux::utils::process_descendents::ProcessDescendantsIterator;
+use crate::linux::utils::process_descendents::ProcessDescendantsIterator;
 
 mod pfnset;
 use pfnset::PfnSet;
diff --git a/lading/src/observer/linux/wss/pfnset.rs b/lading_observer/src/linux/wss/pfnset.rs
similarity index 100%
rename from lading/src/observer/linux/wss/pfnset.rs
rename to lading_observer/src/linux/wss/pfnset.rs

From 7fd67b6eeeff1d66e939a3b007e59ad2a5189adc Mon Sep 17 00:00:00 2001
From: Scott Opell <scott.opell@datadoghq.com>
Date: Wed, 14 Jan 2026 22:05:12 +0000
Subject: [PATCH 2/4] feat(observer): make modules and functions public for
 external consumption

Make linux, cgroup, procfs modules and key functions public to allow
external crates like fgm-observer to use the polling APIs directly
without going through the Server interface.

Public API changes:
- linux module (lib.rs)
- cgroup, procfs modules (linux.rs)
- v2 module (cgroup.rs)
- memory module (procfs.rs)
- smaps_rollup module (procfs/memory.rs)
- poll function (cgroup/v2.rs)
---
 lading_observer/src/lib.rs                 | 2 +-
 lading_observer/src/linux.rs               | 4 ++--
 lading_observer/src/linux/cgroup.rs        | 2 +-
 lading_observer/src/linux/cgroup/v2.rs     | 2 +-
 lading_observer/src/linux/procfs.rs        | 2 +-
 lading_observer/src/linux/procfs/memory.rs | 2 +-
 6 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/lading_observer/src/lib.rs b/lading_observer/src/lib.rs
index da3fdea56..25db58957 100644
--- a/lading_observer/src/lib.rs
+++ b/lading_observer/src/lib.rs
@@ -16,7 +16,7 @@ use serde::Deserialize;
 use tokio::sync::broadcast;
 
 #[cfg(target_os = "linux")]
-mod linux;
+pub mod linux;
 
 /// Type used to receive the target PID once it is running.
 pub type TargetPidReceiver = broadcast::Receiver<Option<i32>>;
diff --git a/lading_observer/src/linux.rs b/lading_observer/src/linux.rs
index 5b1347a1c..6fff4cd14 100644
--- a/lading_observer/src/linux.rs
+++ b/lading_observer/src/linux.rs
@@ -1,5 +1,5 @@
-mod cgroup;
-mod procfs;
+pub mod cgroup;
+pub mod procfs;
 mod utils;
 mod wss;
 
diff --git a/lading_observer/src/linux/cgroup.rs b/lading_observer/src/linux/cgroup.rs
index 73de6abd5..8b46843e7 100644
--- a/lading_observer/src/linux/cgroup.rs
+++ b/lading_observer/src/linux/cgroup.rs
@@ -1,5 +1,5 @@
 /// Code to read cgroup information.
-pub(crate) mod v2;
+pub mod v2;
 
 use std::{collections::VecDeque, io, path::PathBuf};
 
diff --git a/lading_observer/src/linux/cgroup/v2.rs b/lading_observer/src/linux/cgroup/v2.rs
index 4d435e57d..186277dd5 100644
--- a/lading_observer/src/linux/cgroup/v2.rs
+++ b/lading_observer/src/linux/cgroup/v2.rs
@@ -52,7 +52,7 @@ pub(crate) async fn get_path(pid: i32) -> Result<PathBuf, Error> {
 /// Polls for any cgroup metrics that can be read, v2 version.
 #[tracing::instrument(skip_all)]
 #[allow(clippy::too_many_lines)]
-pub(crate) async fn poll(file_path: &Path, labels: &[(String, String)]) -> Result<(), Error> {
+pub async fn poll(file_path: &Path, labels: &[(String, String)]) -> Result<(), Error> {
     // Read all files in the cgroup `path` and create metrics for them. If we
     // lack permissions to read we skip the file. We do not use ? to allow for
     // the maximal number of files to be read.
diff --git a/lading_observer/src/linux/procfs.rs b/lading_observer/src/linux/procfs.rs
index 5cbe7c4c1..ccc6a212e 100644
--- a/lading_observer/src/linux/procfs.rs
+++ b/lading_observer/src/linux/procfs.rs
@@ -1,5 +1,5 @@
 /// Sampler implementation for procfs filesystems
-mod memory;
+pub mod memory;
 mod stat;
 mod uptime;
 mod vmstat;
diff --git a/lading_observer/src/linux/procfs/memory.rs b/lading_observer/src/linux/procfs/memory.rs
index 99775a7fc..1a6edc2b6 100644
--- a/lading_observer/src/linux/procfs/memory.rs
+++ b/lading_observer/src/linux/procfs/memory.rs
@@ -1,5 +1,5 @@
 pub(crate) mod smaps;
-pub(crate) mod smaps_rollup;
+pub mod smaps_rollup;
 
 const BYTES_PER_KIBIBYTE: u64 = 1024;
 

From 508b213bd83f22715e28c5c3c31b0473f1f8dc42 Mon Sep 17 00:00:00 2001
From: Scott Opell <scott.opell@datadoghq.com>
Date: Wed, 14 Jan 2026 22:05:54 +0000
Subject: [PATCH 3/4] feat(observer): make smaps_rollup types and functions
 public

Make Aggregator struct, poll function, and Error enum public in smaps_rollup
module to allow external crates to use memory sampling functionality.
---
 .../src/linux/procfs/memory/smaps_rollup.rs            | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/lading_observer/src/linux/procfs/memory/smaps_rollup.rs b/lading_observer/src/linux/procfs/memory/smaps_rollup.rs
index 17c6b777d..d3aada3fe 100644
--- a/lading_observer/src/linux/procfs/memory/smaps_rollup.rs
+++ b/lading_observer/src/linux/procfs/memory/smaps_rollup.rs
@@ -6,7 +6,7 @@ use super::{BYTES_PER_KIBIBYTE, next_token};
 
 #[derive(thiserror::Error, Debug)]
 /// Errors produced by functions in this module
-pub(crate) enum Error {
+pub enum Error {
     /// Wrapper for [`std::io::Error`]
     #[error("IO error: {0}")]
     Io(#[from] std::io::Error),
@@ -17,13 +17,13 @@ pub(crate) enum Error {
 }
 
 #[derive(Debug, Clone, Copy, Default)]
-pub(crate) struct Aggregator {
-    pub(crate) rss: u64,
-    pub(crate) pss: u64,
+pub struct Aggregator {
+    pub rss: u64,
+    pub pss: u64,
 }
 
 // Read `/proc/{pid}/smaps_rollup` and parse it directly into metrics.
-pub(crate) async fn poll(
+pub async fn poll(
     pid: i32,
     labels: &[(&'static str, String)],
     aggr: &mut Aggregator,

From dc40d1b55842675540f546c7e2a4f7b08a7ed575 Mon Sep 17 00:00:00 2001
From: Scott Opell <scott.opell@datadoghq.com>
Date: Thu, 15 Jan 2026 18:05:07 +0000
Subject: [PATCH 4/4] Add num_cpus dependency and documentation for public APIs

- Add num_cpus to workspace dependencies for CPU count detection
- Document all public modules, types, and functions to satisfy linter
- Fix missing docs for linux, cgroup, procfs modules
- Add comprehensive error variant documentation
---
 Cargo.lock                                    | 23 ++++++++++++++++---
 Cargo.toml                                    |  1 +
 lading_observer/Cargo.toml                    |  1 +
 lading_observer/src/lib.rs                    |  1 +
 lading_observer/src/linux.rs                  |  2 ++
 lading_observer/src/linux/cgroup/v2.rs        |  6 +++++
 lading_observer/src/linux/procfs/memory.rs    |  1 +
 .../src/linux/procfs/memory/smaps_rollup.rs   | 11 ++++++++-
 8 files changed, 42 insertions(+), 4 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 5afdef675..ef9520172 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1843,7 +1843,6 @@ dependencies = [
  "flate2",
  "fuser",
  "futures",
- "heck",
  "http",
  "http-body-util",
  "http-serde",
@@ -1854,6 +1853,7 @@ dependencies = [
  "kube-core",
  "lading-capture",
  "lading-capture-schema",
+ "lading-observer",
  "lading-payload",
  "lading-signal",
  "lading-throttle",
@@ -1861,12 +1861,10 @@ dependencies = [
  "metrics-exporter-prometheus",
  "metrics-util",
  "nix 0.30.1",
- "num-traits",
  "num_cpus",
  "once_cell",
  "opentelemetry-proto",
  "parquet",
- "procfs",
  "proptest",
  "prost",
  "prost-build",
@@ -1940,6 +1938,25 @@ dependencies = [
 name = "lading-fuzz"
 version = "0.1.0"
 
+[[package]]
+name = "lading-observer"
+version = "0.1.0"
+dependencies = [
+ "heck",
+ "lading-signal",
+ "metrics",
+ "nix 0.30.1",
+ "num-traits",
+ "num_cpus",
+ "procfs",
+ "regex",
+ "rustc-hash",
+ "serde",
+ "thiserror 2.0.17",
+ "tokio",
+ "tracing",
+]
+
 [[package]]
 name = "lading-payload"
 version = "0.1.0"
diff --git a/Cargo.toml b/Cargo.toml
index a345747dd..5ac3f938a 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -64,6 +64,7 @@ hyper-util = { version = "0.1", default-features = false }
 heck = { version = "0.5", default-features = false }
 nix = { version = "0.30" }
 num-traits = { version = "0.2", default-features = false }
+num_cpus = "1.17"
 regex = { version = "1.12" }
 sysinfo = { version = "0.37", default-features = false }
 opentelemetry-proto = "0.31"
diff --git a/lading_observer/Cargo.toml b/lading_observer/Cargo.toml
index 07e4b3624..fddb1272d 100644
--- a/lading_observer/Cargo.toml
+++ b/lading_observer/Cargo.toml
@@ -17,6 +17,7 @@ lading-signal = { version = "0.1", path = "../lading_signal" }
 metrics = { workspace = true }
 nix = { workspace = true, features = ["fs", "signal"] }
 num-traits = { workspace = true }
+num_cpus = { workspace = true }
 procfs = { version = "0.18", default-features = false, features = [] }
 regex = { workspace = true }
 rustc-hash = { workspace = true }
diff --git a/lading_observer/src/lib.rs b/lading_observer/src/lib.rs
index 25db58957..c75fb3c15 100644
--- a/lading_observer/src/lib.rs
+++ b/lading_observer/src/lib.rs
@@ -16,6 +16,7 @@ use serde::Deserialize;
 use tokio::sync::broadcast;
 
 #[cfg(target_os = "linux")]
+/// Linux-specific observer functionality for cgroups and procfs.
 pub mod linux;
 
 /// Type used to receive the target PID once it is running.
diff --git a/lading_observer/src/linux.rs b/lading_observer/src/linux.rs
index 6fff4cd14..b28ccf4c1 100644
--- a/lading_observer/src/linux.rs
+++ b/lading_observer/src/linux.rs
@@ -1,4 +1,6 @@
+/// Cgroup v2 metrics collection.
 pub mod cgroup;
+/// Procfs metrics collection.
 pub mod procfs;
 mod utils;
 mod wss;
diff --git a/lading_observer/src/linux/cgroup/v2.rs b/lading_observer/src/linux/cgroup/v2.rs
index 186277dd5..d4239729a 100644
--- a/lading_observer/src/linux/cgroup/v2.rs
+++ b/lading_observer/src/linux/cgroup/v2.rs
@@ -13,15 +13,21 @@ use tokio::fs;
 use tracing::{debug, error, warn};
 
 #[derive(thiserror::Error, Debug)]
+/// Errors that can occur during cgroup v2 operations.
 pub enum Error {
+    /// I/O error.
     #[error("IO error: {0}")]
     Io(#[from] std::io::Error),
+    /// Integer parsing error.
     #[error("Parse int error: {0}")]
     ParseInt(#[from] std::num::ParseIntError),
+    /// Float parsing error.
     #[error("Parse float error: {0}")]
     ParseFloat(#[from] std::num::ParseFloatError),
+    /// Cgroup v2 not found.
     #[error("Cgroup v2 not found")]
     CgroupV2NotFound,
+    /// PSI parsing error.
     #[error("Parsing PSI error: {0}")]
     ParsingPsi(String),
 }
diff --git a/lading_observer/src/linux/procfs/memory.rs b/lading_observer/src/linux/procfs/memory.rs
index 1a6edc2b6..629401396 100644
--- a/lading_observer/src/linux/procfs/memory.rs
+++ b/lading_observer/src/linux/procfs/memory.rs
@@ -1,4 +1,5 @@
 pub(crate) mod smaps;
+/// Memory metrics from /proc/[pid]/smaps_rollup.
 pub mod smaps_rollup;
 
 const BYTES_PER_KIBIBYTE: u64 = 1024;
diff --git a/lading_observer/src/linux/procfs/memory/smaps_rollup.rs b/lading_observer/src/linux/procfs/memory/smaps_rollup.rs
index d3aada3fe..923342ee3 100644
--- a/lading_observer/src/linux/procfs/memory/smaps_rollup.rs
+++ b/lading_observer/src/linux/procfs/memory/smaps_rollup.rs
@@ -10,19 +10,28 @@ pub enum Error {
     /// Wrapper for [`std::io::Error`]
     #[error("IO error: {0}")]
     Io(#[from] std::io::Error),
+    /// Integer parsing error.
     #[error("Number Parsing: {0}")]
     ParseInt(#[from] std::num::ParseIntError),
+    /// Parsing error.
     #[error("Parsing: {0}")]
     Parsing(String),
 }
 
 #[derive(Debug, Clone, Copy, Default)]
+/// Aggregator for memory metrics from smaps_rollup.
 pub struct Aggregator {
+    /// Resident Set Size in bytes.
     pub rss: u64,
+    /// Proportional Set Size in bytes.
     pub pss: u64,
 }
 
-// Read `/proc/{pid}/smaps_rollup` and parse it directly into metrics.
+/// Read `/proc/{pid}/smaps_rollup` and parse it directly into metrics.
+///
+/// # Errors
+///
+/// Returns an error if the file cannot be read or parsed.
 pub async fn poll(
     pid: i32,
     labels: &[(&'static str, String)],