add Dockerfile and Rocky Linux 9 build docs

Introduces a Docker-based build path so ior can be compiled on any
Linux host without a native Rocky 9 toolchain setup:

- Dockerfile: Rocky 9 minimal image with Go (version from ARG, default
  from go.mod), static libelf/libzstd built from source, libbpfgo at
  v0.9.2-libbpf-1.5.1, and mage; CMD runs mage generate + mage all
  against the repo root mounted as a volume.
- scripts/build-with-docker.sh: reads GO_VERSION from go.mod, passes it
  as --build-arg to docker build, mounts tracefs and BTF into the
  container, writes the binary to the repo root.
- Magefile.go: adds BuildDocker target that wraps the script.
- README.md: simplified to the two build paths (Docker + native) with
  links to docs/; removed GOTOOLCHAIN=auto throughout.
- docs/build-rocky-linux-9.md: full manual Rocky 9 steps, libbpfgo
  toolchain setup/rollback, compile-once-run-everywhere explanation,
  and timing semantics.
- docs/tui-reference.md: complete TUI hotkey reference, recording mode
  details, and the .ior.zst vs Parquet trade-off table.
- AGENTS.md: removed GOTOOLCHAIN=auto from all build commands.
- internal/c/generated_tracepoints.c: regenerated against the host kernel.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 50 insertions, 0 deletions

diff --git a/scripts/build-with-docker.sh b/scripts/build-with-docker.sh
new file mode 100755
index 0000000..02eb60f
--- /dev/null
+++ b/scripts/build-with-docker.sh
@@ -0,0 +1,50 @@
+#!/usr/bin/env bash
+# Build the ior binary inside a Rocky Linux 9 container and write it to the
+# current directory.  The container image is built once and reused on subsequent
+# runs.  The ior source tree is mounted as a volume so the resulting binary
+# lands directly in $(pwd)/ior.
+#
+# Usage:
+#   ./build-with-docker.sh          # build image + compile ior
+#   ./build-with-docker.sh --build  # force rebuild of the Docker image
+#   ./build-with-docker.sh --run    # skip image build, only compile ior
+set -euo pipefail
+
+IMAGE="ior-builder:rocky9"
+REPO_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+
+# Derive the Go version from go.mod so the Docker image always matches the
+# minimum toolchain declared by the project.
+GO_VERSION="$(grep '^go ' "${REPO_ROOT}/go.mod" | awk '{print $2}')"
+
+BUILD_IMAGE=true
+RUN_BUILD=true
+
+for arg in "$@"; do
+    case "$arg" in
+        --build) BUILD_IMAGE=true; RUN_BUILD=false ;;
+        --run)   BUILD_IMAGE=false; RUN_BUILD=true  ;;
+    esac
+done
+
+if $BUILD_IMAGE; then
+    echo "==> Building Docker image ${IMAGE} (this takes ~15-20 min on first run)..."
+    docker build --build-arg "GO_VERSION=${GO_VERSION}" -t "${IMAGE}" "${REPO_ROOT}"
+    echo "==> Image build complete."
+fi
+
+if $RUN_BUILD; then
+    echo "==> Compiling ior inside the container..."
+    # --privileged gives full host capabilities.
+    # tracefs (/sys/kernel/tracing) and BTF (/sys/kernel/btf) are not auto-mounted
+    # by Docker even with --privileged, so they are mounted explicitly:
+    #   - /sys/kernel/tracing  : mage generate reads available syscall tracepoints
+    #   - /sys/kernel/btf      : mage bpfBuild reads vmlinux BTF for vmlinux.h
+    docker run --rm \
+        --privileged \
+        -v /sys/kernel/tracing:/sys/kernel/tracing \
+        -v /sys/kernel/btf:/sys/kernel/btf \
+        -v "${REPO_ROOT}:/git/ior" \
+        "${IMAGE}"
+    echo "==> Done. Binary written to ${REPO_ROOT}/ior"
+fi