workflows: add a composite action to execute bpftool build tests

The kernel bpf selftest include the test_bpftool_build.sh script, that
ensures that all supported ways of building bpftool still work as
expected.

Add a dedicated action to allow executing this script in CI.

Signed-off-by: Alexis Lothoré <alexis.lothore@bootlin.com>

Author: Tropicao

build-bpftool/action.yml

@@ -0,0 +1,16 @@
+name: 'Test bpftool build'
+description: 'Run test_bpftool_build.sh to exercise the various ways of building bpftool'
+inputs:
+  kernel-root:
+    description: 'Path to the root of the kernel source tree'
+    required: true
+
+runs:
+  using: "composite"
+  steps:
+    - name: Test bpftool build
+      shell: bash
+      run:
+        ${GITHUB_ACTION_PATH}/build_bpftool.sh "${{ inputs.kernel-root }}"
+      env:
+        MAX_MAKE_JOBS: ${{ inputs.max-make-jobs }}

build-bpftool/build_bpftool.sh

@@ -0,0 +1,23 @@
+#!/bin/bash
+
+set -euo pipefail
+
+THISDIR="$(cd $(dirname $0) && pwd)"
+
+source "${THISDIR}"/../helpers.sh
+
+KERNEL_ROOT="$(realpath $1)"
+
+foldable start build_bpftool "Testing bpftool build"
+
+# The action builds everything in tools/bpf; that includes bpf_dbg, which
+# depends on readline
+sudo -E apt-get install --no-install-recommends -y \
+     libreadline-dev
+
+cd "${KERNEL_ROOT}"
+
+unset CROSS_COMPILE
+bash tools/testing/selftests/bpf/test_bpftool_build.sh -j "$(kernel_build_make_jobs)"
+
+foldable end build_bpftool