[PATCH v5 4/4] selftests: cgroup: handle vmtest-dmem -b to test locally built kernel

[Albert Esteve <aesteve@redhat.com>]

Currently vmtest-dmem.sh relies on the host's running kernel or a
pre-built one when booting the virtme-ng VM, with no option to
configure and build a local kernel tree directly.

This adds friction to the development cycle: the user must manually
run vng --kconfig with the correct config fragment, build the kernel,
and pass the result to the script.

Add a -b flag that automates this workflow.  When set, handle_build()
configures the kernel using vng --kconfig with the selftest config
fragment, builds it with make -j$(nproc), and run_vm() passes the
local tree to vng --run so the VM boots the freshly built kernel.

Signed-off-by: Eric Chanudet <echanude@redhat.com>
Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
 tools/testing/selftests/cgroup/vmtest-dmem.sh | 47 ++++++++++++++++++++++++---
 1 file changed, 43 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/cgroup/vmtest-dmem.sh b/tools/testing/selftests/cgroup/vmtest-dmem.sh
index 0bb6529112b54..4d0e2c0511e5b 100755
--- a/tools/testing/selftests/cgroup/vmtest-dmem.sh
+++ b/tools/testing/selftests/cgroup/vmtest-dmem.sh
@@ -15,6 +15,7 @@ readonly KERNEL_CHECKOUT="$(realpath "${SCRIPT_DIR}"/../../../../)"
 
 source "${SCRIPT_DIR}"/../kselftest/ktap_helpers.sh
 
+BUILD=0
 QEMU="qemu-system-$(uname -m)"
 VERBOSE=0
 SHELL_MODE=0
@@ -26,10 +27,22 @@ function usage() {
 	cat <<EOF
 $0 [OPTIONS]
 Options:
+	-b	Build kernel from source tree before booting
 	-q	QEMU binary/path (default: ${QEMU})
 	-s	Start interactive shell in VM instead of running tests
 	-v	Verbose output (vng boot logs on stdout)
 	-h	Display this help
+
+If you build your kernel using KBUILD_OUTPUT= or O= options, these
+can be passed as environment variables to the script:
+
+  O=<build_path> $0 -b
+
+or
+
+  KBUILD_OUTPUT=<build_path> $0 -b
+
+O= takes precedence over KBUILD_OUTPUT= if both are set.
 EOF
 }
 
@@ -60,17 +73,41 @@ function check_deps() {
 	done
 }
 
+function handle_build() {
+	[[ "${BUILD}" -eq 1 ]] || return 0
+
+	[[ -f "${KERNEL_CHECKOUT}/kernel/cgroup/dmem_selftest.c" ]] || \
+		fail "-b requires vmtest-dmem.sh called from the kernel source tree"
+
+	# Figure out where the kernel is being built.
+	# O takes precedence over KBUILD_OUTPUT.
+	local out_args=()
+	if [[ -n "${O:-}" ]]; then
+		out_args=(O="${O}")
+	elif [[ -n "${KBUILD_OUTPUT:-}" ]]; then
+		out_args=(KBUILD_OUTPUT="${KBUILD_OUTPUT}")
+	fi
+
+	pushd "${KERNEL_CHECKOUT}" &>/dev/null
+	vng --kconfig --config "${SCRIPT_DIR}"/config "${out_args[@]}" || \
+		fail "failed to generate .config for kernel source tree (${KERNEL_CHECKOUT})"
+	make "${out_args[@]}" -j"$(nproc 2>/dev/null || echo 1)" || \
+		fail "failed to build kernel from source tree (${KERNEL_CHECKOUT})"
+	popd &>/dev/null
+}
+
 # Run vng with common flags. Extra arguments are appended by the caller:
 #   --exec <script>  for automated test runs
 #   (nothing)        for interactive shell mode
 function run_vm() {
-	local verbose_opt=""
+	local vng_args=()
 
-	[[ "${VERBOSE}" -eq 1 ]] && verbose_opt="--verbose"
+	[[ "${BUILD}" -eq 1 ]] && vng_args+=("${KERNEL_CHECKOUT}")
+	[[ "${VERBOSE}" -eq 1 ]] && vng_args+=("--verbose")
 
 	vng \
 		--run \
-		${verbose_opt:+"${verbose_opt}"} \
+		"${vng_args[@]}" \
 		--qemu="$(command -v "${QEMU}")" \
 		--user root \
 		--rw \
@@ -78,10 +115,11 @@ function run_vm() {
 }
 
 function main() {
-	while getopts ':hvq:s' opt; do
+	while getopts ':hvq:sb' opt; do
 		case "${opt}" in
 		v) VERBOSE=1 ;;
 		q) QEMU="${OPTARG}" ;;
+		b) BUILD=1 ;;
 		s) SHELL_MODE=1 ;;
 		h) usage; exit 0 ;;
 		*) usage; exit 1 ;;
@@ -89,6 +127,7 @@ function main() {
 	done
 
 	check_deps
+	handle_build
 
 	if [[ "${SHELL_MODE}" -eq 1 ]]; then
 		echo "Starting interactive shell in VM. Exit to stop VM."

-- 
2.54.0