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, 75 insertions, 0 deletions

diff --git a/Dockerfile b/Dockerfile
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index 0000000..d190056
--- /dev/null
+++ b/Dockerfile
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+FROM rockylinux:9-minimal
+
+# Update GO_VERSION here to upgrade the Go toolchain baked into the image.
+ARG GO_VERSION=1.26.2
+
+# Install full dnf and plugin support (minimal image ships only microdnf)
+RUN microdnf install -y dnf dnf-plugins-core && \
+    microdnf clean all
+
+# Enable CRB (ships zlib-static / glibc-static), EPEL, and the BaseOS source
+# repo (provides the elfutils source RPM needed to build libelf.a).
+RUN dnf config-manager --set-enabled crb && \
+    dnf config-manager --set-enabled baseos-source && \
+    dnf install -y epel-release && \
+    dnf clean all
+
+# Build-time toolchain: C compiler, clang/LLVM (for BPF), bpftool, BPF/elf
+# headers, static archives for zlib and glibc, and packaging helpers.
+RUN dnf install -y \
+        gcc clang bpftool \
+        elfutils-libelf-devel \
+        zlib-static glibc-static libzstd-devel \
+        git make cmake wget rpmdevtools && \
+    dnf builddep -y elfutils && \
+    dnf clean all
+
+# Install Go from go.dev — Rocky 9 ships an older release, ior needs 1.26+.
+RUN wget -q "https://go.dev/dl/go${GO_VERSION}.linux-amd64.tar.gz" -O /tmp/go.tar.gz && \
+    tar -C /usr/local -xf /tmp/go.tar.gz && \
+    rm /tmp/go.tar.gz
+
+ENV PATH="/usr/local/go/bin:/root/go/bin:${PATH}"
+ENV GOPATH="/root/go"
+
+# Build libelf.a from the Rocky 9 elfutils source RPM.
+# Rocky 9 does not ship libelf.a (no *-static packages exist in the distro).
+RUN mkdir -p /root/src && cd /root && \
+    dnf download --source elfutils-libelf && \
+    rpm -ivh elfutils-*.src.rpm && \
+    tar -C /root/src -xjf rpmbuild/SOURCES/elfutils-*.tar.bz2 && \
+    cd /root/src/elfutils-* && \
+    ./configure --enable-deterministic-archives --disable-debuginfod --disable-libdebuginfod && \
+    make -C lib -j$(nproc) && \
+    make -C libelf -j$(nproc) && \
+    cp -v libelf/libelf.a /usr/lib64/ && \
+    rm -rf /root/src /root/rpmbuild /root/elfutils-*.src.rpm
+
+# Build libzstd.a from upstream — libzstd-devel does not ship the static archive.
+RUN wget -q https://github.com/facebook/zstd/releases/download/v1.5.5/zstd-1.5.5.tar.gz \
+        -O /tmp/zstd.tar.gz && \
+    tar -C /tmp -xzf /tmp/zstd.tar.gz && \
+    make -C /tmp/zstd-1.5.5/lib -j$(nproc) libzstd.a && \
+    cp -v /tmp/zstd-1.5.5/lib/libzstd.a /usr/lib64/ && \
+    rm -rf /tmp/zstd-1.5.5 /tmp/zstd.tar.gz
+
+# Clone libbpfgo at the required tag and build the static archive.
+# Placed at /git/libbpfgo so it is a sibling of the ior mount at /git/ior,
+# matching the default LIBBPFGO=../libbpfgo path used by Magefile.go.
+RUN mkdir -p /git && \
+    git clone https://github.com/aquasecurity/libbpfgo /git/libbpfgo && \
+    git -C /git/libbpfgo checkout v0.9.2-libbpf-1.5.1 && \
+    git -C /git/libbpfgo submodule update --init --recursive && \
+    make -C /git/libbpfgo libbpfgo-static
+
+# Install the mage build tool
+RUN go install github.com/magefile/mage@latest
+
+# The ior source tree is mounted at /git/ior at runtime (see build-with-docker.sh).
+WORKDIR /git/ior
+
+# Generate kernel-specific tracepoint code then compile the static ior binary.
+# IOR_FORCE_GENERATE=1 skips the strict diff against the committed syscall-coverage
+# audit, which was generated on a different kernel build than the container host.
+# The container runs as root so bpftool and /sys/kernel/tracing are used directly.
+CMD ["sh", "-c", "IOR_FORCE_GENERATE=1 mage generate && mage all"]