Add support for cgroup limits (#443)

* Add cgroup package

* Refactor procGgroup

* Add testdata generation

* Add v1 testdata generation

* Move scripts around

* Add integration test in CI

* Remove cgroup v1

* Move to cgroup struct

* Remove half-core test as it's redundant

2 files changed, 90 insertions, 0 deletions

diff --git a/bin/gen-cgroup-testdata b/bin/gen-cgroup-testdata
new file mode 100755
index 0000000..3d9215b
--- /dev/null
+++ b/bin/gen-cgroup-testdata
@@ -0,0 +1,48 @@
+#!/usr/bin/env bash
+#
+# gen-cgroup-testdata - Generate cgroup testdata by running
+# bin/snapshot-cgroup inside Docker containers with known resource limits.
+#
+# Usage: gen-cgroup-testdata
+#
+# Prerequisites: Docker on a host running cgroup v2.
+#
+# Each testdata directory contains:
+#   expected.json  - {"cpu_quota": <float>, "memory_limit": <int>}
+#   proc/          - snapshot of /proc/self/cgroup
+#   sys/           - snapshot of cgroup control files
+
+set -euo pipefail
+
+cd "$(dirname "$0")/.."
+
+testdata="cgroup/testdata"
+snapshot_script="bin/snapshot-cgroup"
+
+generate() {
+    local name="$1" cpu_quota="$2" memory_limit="$3"
+    shift 3
+    local outdir="$testdata/$name"
+
+    echo "Generating $name..."
+    rm -rf "$outdir"
+    mkdir -p "$outdir"
+
+    docker run --rm \
+        --user "$(id -u):$(id -g)" \
+        "$@" \
+        -v "$PWD/$snapshot_script:/snapshot:ro" \
+        -v "$PWD/$outdir:/out" \
+        debian:bookworm-slim \
+        /snapshot /out
+
+    cat > "$outdir/expected.json" <<EOF
+{"cpu_quota": $cpu_quota, "memory_limit": $memory_limit}
+EOF
+}
+
+generate "v2-two-cores-256m"   2.0  268435456  --cpus=2   --memory=256m
+generate "v2-quarter-core-64m" 0.25 67108864   --cpus=0.25 --memory=64m
+generate "v2-no-limit"         null null
+
+echo "v2 testdata generated successfully."
diff --git a/bin/snapshot-cgroup b/bin/snapshot-cgroup
new file mode 100755
index 0000000..5fed85f
--- /dev/null
+++ b/bin/snapshot-cgroup
@@ -0,0 +1,42 @@
+#!/usr/bin/env bash
+#
+# snapshot-cgroup - Copy cgroup v2 files from the live system into a
+# directory tree suitable for use with TestIntegrationCgroupLimits.
+#
+# Usage: snapshot-cgroup <output-dir>
+#
+# The script reads /proc/self/cgroup to find the v2 group path and copies
+# exactly the files that the cgroup package needs:
+#
+#   proc/self/cgroup
+#   sys/fs/cgroup/<group>/cpu.max
+#   sys/fs/cgroup/<group>/memory.max
+
+set -euo pipefail
+
+if [[ $# -ne 1 ]]; then
+    echo "Usage: $0 <output-dir>" >&2
+    exit 1
+fi
+
+out="$1"
+mkdir -p "$out"
+
+copy_file() {
+    local src="$1" dst="$out/$2"
+    mkdir -p "$(dirname "$dst")"
+    cp "$src" "$dst"
+}
+
+copy_file /proc/self/cgroup proc/self/cgroup
+
+group=$(awk -F: '/^0::/ { print $3 }' /proc/self/cgroup)
+cgdir="/sys/fs/cgroup${group}"
+
+for f in cpu.max memory.max; do
+    if [[ -f "$cgdir/$f" ]]; then
+        copy_file "$cgdir/$f" "sys/fs/cgroup${group}/$f"
+    fi
+done
+
+echo "Snapshot written to $out"