Merge branch 'BPF selftest helper script'

KP Singh says:

====================

# v4 -> v5

- Use %Y (modification time) instead of %W (creation time) of the local
  copy of the kernel config to check for newer upstream config.
- Rename the script to vmtest.sh

# v3 -> v4

- Fix logic for updating kernel config to not download the file
  if there are no upstream modifications and avoid extraneous
  kernel compilation as suggested by Andrii.
- This also removes the need for the -k flag.

# v2 -> v3

- Fixes to silence verbose commands
- Fixed output buffering without being teed out
- Fixed the clobbered error code of the script
- Other fixes suggested by Andrii

# v1 -> v2

- The script now compiles the kernel by default, and the -k option
  implies "keep the kernel"
- Pointer to the script in the docs.
- Some minor simplifications.

Allow developers and contributors to understand if their changes would
end up breaking the BPF CI and avoid the back and forth required for
fixing the test cases in the CI environment. The se
====================
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

tools/testing/selftests/bpf/README.rst

@@ -6,6 +6,30 @@ General instructions on running selftests can be found in
 
 __ /Documentation/bpf/bpf_devel_QA.rst#q-how-to-run-bpf-selftests
 
+=========================
+Running Selftests in a VM
+=========================
+
+It's now possible to run the selftests using ``tools/testing/selftests/bpf/vmtest.sh``.
+The script tries to ensure that the tests are run with the same environment as they
+would be run post-submit in the CI used by the Maintainers.
+
+This script downloads a suitable Kconfig and VM userspace image from the system used by
+the CI. It builds the kernel (without overwriting your existing Kconfig), recompiles the
+bpf selftests, runs them (by default ``tools/testing/selftests/bpf/test_progs``) and
+saves the resulting output (by default in ``~/.bpf_selftests``).
+
+For more information on about using the script, run:
+
+.. code-block:: console
+
+  $ tools/testing/selftests/bpf/vmtest.sh -h
+
+.. note:: The script uses pahole and clang based on host environment setting.
+          If you want to change pahole and llvm, you can change `PATH` environment
+          variable in the beginning of script.
+
+.. note:: The script currently only supports x86_64.
 
 Additional information about selftest failures are
 documented here.

tools/testing/selftests/bpf/vmtest.sh

+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+set -u
+set -e
+
+# This script currently only works for x86_64, as
+# it is based on the VM image used by the BPF CI which is
+# x86_64.
+QEMU_BINARY="${QEMU_BINARY:="qemu-system-x86_64"}"
+X86_BZIMAGE="arch/x86/boot/bzImage"
+DEFAULT_COMMAND="./test_progs"
+MOUNT_DIR="mnt"
+ROOTFS_IMAGE="root.img"
+OUTPUT_DIR="$HOME/.bpf_selftests"
+KCONFIG_URL="https://raw.githubusercontent.com/libbpf/libbpf/master/travis-ci/vmtest/configs/latest.config"
+KCONFIG_API_URL="https://api.github.com/repos/libbpf/libbpf/contents/travis-ci/vmtest/configs/latest.config"
+INDEX_URL="https://raw.githubusercontent.com/libbpf/libbpf/master/travis-ci/vmtest/configs/INDEX"
+NUM_COMPILE_JOBS="$(nproc)"
+
+usage()
+{
+	cat <<EOF
+Usage: $0 [-i] [-d <output_dir>] -- [<command>]
+
+<command> is the command you would normally run when you are in
+tools/testing/selftests/bpf. e.g:
+
+	$0 -- ./test_progs -t test_lsm
+
+If no command is specified, "${DEFAULT_COMMAND}" will be run by
+default.
+
+If you build your kernel using KBUILD_OUTPUT= or O= options, these
+can be passed as environment variables to the script:
+
+  O=<kernel_build_path> $0 -- ./test_progs -t test_lsm
+
+or
+
+  KBUILD_OUTPUT=<kernel_build_path> $0 -- ./test_progs -t test_lsm
+
+Options:
+
+	-i)		Update the rootfs image with a newer version.
+	-d)		Update the output directory (default: ${OUTPUT_DIR})
+	-j)		Number of jobs for compilation, similar to -j in make
+			(default: ${NUM_COMPILE_JOBS})
+EOF
+}
+
+unset URLS
+populate_url_map()
+{
+	if ! declare -p URLS &> /dev/null; then
+		# URLS contain the mapping from file names to URLs where
+		# those files can be downloaded from.
+		declare -gA URLS
+		while IFS=$'\t' read -r name url; do
+			URLS["$name"]="$url"
+		done < <(curl -Lsf ${INDEX_URL})
+	fi
+}
+
+download()
+{
+	local file="$1"
+
+	if [[ ! -v URLS[$file] ]]; then
+		echo "$file not found" >&2
+		return 1
+	fi
+
+	echo "Downloading $file..." >&2
+	curl -Lsf "${URLS[$file]}" "${@:2}"
+}
+
+newest_rootfs_version()
+{
+	{
+	for file in "${!URLS[@]}"; do
+		if [[ $file =~ ^libbpf-vmtest-rootfs-(.*)\.tar\.zst$ ]]; then
+			echo "${BASH_REMATCH[1]}"
+		fi
+	done
+	} | sort -rV | head -1
+}
+
+download_rootfs()
+{
+	local rootfsversion="$1"
+	local dir="$2"
+
+	if ! which zstd &> /dev/null; then
+		echo 'Could not find "zstd" on the system, please install zstd'
+		exit 1
+	fi
+
+	download "libbpf-vmtest-rootfs-$rootfsversion.tar.zst" |
+		zstd -d | sudo tar -C "$dir" -x
+}
+
+recompile_kernel()
+{
+	local kernel_checkout="$1"
+	local make_command="$2"
+
+	cd "${kernel_checkout}"
+
+	${make_command} olddefconfig
+	${make_command}
+}
+
+mount_image()
+{
+	local rootfs_img="${OUTPUT_DIR}/${ROOTFS_IMAGE}"
+	local mount_dir="${OUTPUT_DIR}/${MOUNT_DIR}"
+
+	sudo mount -o loop "${rootfs_img}" "${mount_dir}"
+}
+
+unmount_image()
+{
+	local mount_dir="${OUTPUT_DIR}/${MOUNT_DIR}"
+
+	sudo umount "${mount_dir}" &> /dev/null
+}
+
+update_selftests()
+{
+	local kernel_checkout="$1"
+	local selftests_dir="${kernel_checkout}/tools/testing/selftests/bpf"
+
+	cd "${selftests_dir}"
+	${make_command}
+
+	# Mount the image and copy the selftests to the image.
+	mount_image
+	sudo rm -rf "${mount_dir}/root/bpf"
+	sudo cp -r "${selftests_dir}" "${mount_dir}/root"
+	unmount_image
+}
+
+update_init_script()
+{
+	local init_script_dir="${OUTPUT_DIR}/${MOUNT_DIR}/etc/rcS.d"
+	local init_script="${init_script_dir}/S50-startup"
+	local command="$1"
+	local log_file="$2"
+
+	mount_image
+
+	if [[ ! -d "${init_script_dir}" ]]; then
+		cat <<EOF
+Could not find ${init_script_dir} in the mounted image.
+This likely indicates a bad rootfs image, Please download
+a new image by passing "-i" to the script
+EOF
+		exit 1
+
+	fi
+
+	sudo bash -c "cat >${init_script}" <<EOF
+#!/bin/bash
+
+{
+	cd /root/bpf
+	echo ${command}
+	stdbuf -oL -eL ${command}
+} 2>&1 | tee /root/${log_file}
+poweroff -f
+EOF
+
+	sudo chmod a+x "${init_script}"
+	unmount_image
+}
+
+create_vm_image()
+{
+	local rootfs_img="${OUTPUT_DIR}/${ROOTFS_IMAGE}"
+	local mount_dir="${OUTPUT_DIR}/${MOUNT_DIR}"
+
+	rm -rf "${rootfs_img}"
+	touch "${rootfs_img}"
+	chattr +C "${rootfs_img}" >/dev/null 2>&1 || true
+
+	truncate -s 2G "${rootfs_img}"
+	mkfs.ext4 -q "${rootfs_img}"
+
+	mount_image
+	download_rootfs "$(newest_rootfs_version)" "${mount_dir}"
+	unmount_image
+}
+
+run_vm()
+{
+	local kernel_bzimage="$1"
+	local rootfs_img="${OUTPUT_DIR}/${ROOTFS_IMAGE}"
+
+	if ! which "${QEMU_BINARY}" &> /dev/null; then
+		cat <<EOF
+Could not find ${QEMU_BINARY}
+Please install qemu or set the QEMU_BINARY environment variable.
+EOF
+		exit 1
+	fi
+
+	${QEMU_BINARY} \
+		-nodefaults \
+		-display none \
+		-serial mon:stdio \
+		-cpu kvm64 \
+		-enable-kvm \
+		-smp 4 \
+		-m 2G \
+		-drive file="${rootfs_img}",format=raw,index=1,media=disk,if=virtio,cache=none \
+		-kernel "${kernel_bzimage}" \
+		-append "root=/dev/vda rw console=ttyS0,115200"
+}
+
+copy_logs()
+{
+	local mount_dir="${OUTPUT_DIR}/${MOUNT_DIR}"
+	local log_file="${mount_dir}/root/$1"
+
+	mount_image
+	sudo cp ${log_file} "${OUTPUT_DIR}"
+	sudo rm -f ${log_file}
+	unmount_image
+}
+
+is_rel_path()
+{
+	local path="$1"
+
+	[[ ${path:0:1} != "/" ]]
+}
+
+update_kconfig()
+{
+	local kconfig_file="$1"
+	local update_command="curl -sLf ${KCONFIG_URL} -o ${kconfig_file}"
+	# Github does not return the "last-modified" header when retrieving the
+	# raw contents of the file. Use the API call to get the last-modified
+	# time of the kernel config and only update the config if it has been
+	# updated after the previously cached config was created. This avoids
+	# unnecessarily compiling the kernel and selftests.
+	if [[ -f "${kconfig_file}" ]]; then
+		local last_modified_date="$(curl -sL -D - "${KCONFIG_API_URL}" -o /dev/null | \
+			grep "last-modified" | awk -F ': ' '{print $2}')"
+		local remote_modified_timestamp="$(date -d "${last_modified_date}" +"%s")"
+		local local_creation_timestamp="$(stat -c %Y "${kconfig_file}")"
+
+		if [[ "${remote_modified_timestamp}" -gt "${local_creation_timestamp}" ]]; then
+			${update_command}
+		fi
+	else
+		${update_command}
+	fi
+}
+
+main()
+{
+	local script_dir="$(cd -P -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd -P)"
+	local kernel_checkout=$(realpath "${script_dir}"/../../../../)
+	local log_file="$(date +"bpf_selftests.%Y-%m-%d_%H-%M-%S.log")"
+	# By default the script searches for the kernel in the checkout directory but
+	# it also obeys environment variables O= and KBUILD_OUTPUT=
+	local kernel_bzimage="${kernel_checkout}/${X86_BZIMAGE}"
+	local command="${DEFAULT_COMMAND}"
+	local update_image="no"
+
+	while getopts 'hkid:j:' opt; do
+		case ${opt} in
+		i)
+			update_image="yes"
+			;;
+		d)
+			OUTPUT_DIR="$OPTARG"
+			;;
+		j)
+			NUM_COMPILE_JOBS="$OPTARG"
+			;;
+		h)
+			usage
+			exit 0
+			;;
+		\? )
+			echo "Invalid Option: -$OPTARG"
+			usage
+			exit 1
+			;;
+		: )
+			echo "Invalid Option: -$OPTARG requires an argument"
+			usage
+			exit 1
+			;;
+		esac
+	done
+	shift $((OPTIND -1))
+
+	if [[ $# -eq 0 ]]; then
+		echo "No command specified, will run ${DEFAULT_COMMAND} in the vm"
+	else
+		command="$@"
+	fi
+
+	local kconfig_file="${OUTPUT_DIR}/latest.config"
+	local make_command="make -j ${NUM_COMPILE_JOBS} KCONFIG_CONFIG=${kconfig_file}"
+
+	# Figure out where the kernel is being built.
+	# O takes precedence over KBUILD_OUTPUT.
+	if [[ "${O:=""}" != "" ]]; then
+		if is_rel_path "${O}"; then
+			O="$(realpath "${PWD}/${O}")"
+		fi
+		kernel_bzimage="${O}/${X86_BZIMAGE}"
+		make_command="${make_command} O=${O}"
+	elif [[ "${KBUILD_OUTPUT:=""}" != "" ]]; then
+		if is_rel_path "${KBUILD_OUTPUT}"; then
+			KBUILD_OUTPUT="$(realpath "${PWD}/${KBUILD_OUTPUT}")"
+		fi
+		kernel_bzimage="${KBUILD_OUTPUT}/${X86_BZIMAGE}"
+		make_command="${make_command} KBUILD_OUTPUT=${KBUILD_OUTPUT}"
+	fi
+
+	populate_url_map
+
+	local rootfs_img="${OUTPUT_DIR}/${ROOTFS_IMAGE}"
+	local mount_dir="${OUTPUT_DIR}/${MOUNT_DIR}"
+
+	echo "Output directory: ${OUTPUT_DIR}"
+
+	mkdir -p "${OUTPUT_DIR}"
+	mkdir -p "${mount_dir}"
+	update_kconfig "${kconfig_file}"
+
+	recompile_kernel "${kernel_checkout}" "${make_command}"
+
+	if [[ "${update_image}" == "no" && ! -f "${rootfs_img}" ]]; then
+		echo "rootfs image not found in ${rootfs_img}"
+		update_image="yes"
+	fi
+
+	if [[ "${update_image}" == "yes" ]]; then
+		create_vm_image
+	fi
+
+	update_selftests "${kernel_checkout}" "${make_command}"
+	update_init_script "${command}" "${log_file}"
+	run_vm "${kernel_bzimage}"
+	copy_logs "${log_file}"
+	echo "Logs saved in ${OUTPUT_DIR}/${log_file}"
+}
+
+catch()
+{
+	local exit_code=$1
+	# This is just a cleanup and the directory may
+	# have already been unmounted. So, don't let this
+	# clobber the error code we intend to return.
+	unmount_image || true
+	exit ${exit_code}
+}
+
+trap 'catch "$?"' EXIT
+
+main "$@"