github: Implement CI as a pull-request workflow

Run the tests under their own bus session to isolate them from the rest
of the test environment

Signed-off-by: Andrew Jeffery <[email protected]>

.github/workflows/pr.yml

@@ -0,0 +1,27 @@
+name: pull-request-ci
+on: [push, pull_request]
+jobs:
+  run-tests:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install system build dependencies
+        run: >
+          sudo apt-get update &&
+          sudo apt-get install libsystemd-dev ninja-build
+
+      - name: Install meson
+        run: pip install --user meson
+
+      - name: Install python dependencies for mctp tests
+        run: pip install --user -r tests/requirements.txt
+
+      - name: Configure mctp build
+        run: meson setup build
+
+      - name: Build mctp
+        run: meson compile -C build
+
+      - name: Test mctp
+        run: meson test -C build

CHANGELOG.md

@@ -17,4 +17,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 1. dbus interface: the NetworkID field is now a `u` rather than an `i`, to
    match OpenBMC's MCTP endpoint specification
 
+2. Use Github Actions for CI
+
+   Note that this bumps the meson requirement from >=0.47.0 to >=0.59.0. The
+   bump allows us to exploit some features helpful for chaining the solution
+   together.
+
 ## [1.1] - 2023-04-13

meson.build

@@ -2,7 +2,7 @@
 #
 project(
     'mctp', 'c',
-    meson_version: '>= 0.47.0',
+    meson_version: '>= 0.59.0',
     version: 'v1.1',
     license: 'GPLv2',
     default_options: [
@@ -11,6 +11,7 @@ project(
 )
 
 cc = meson.get_compiler('c')
+
 add_project_arguments('-Wno-unused-parameter', language : 'c')
 
 libsystemd = dependency('libsystemd', version: '>=247', required: false)
@@ -80,12 +81,46 @@ configure_file(
     configuration: test_conf_data,
 )
 
-pytest = find_program('pytest', required: false)
-
-if pytest.found()
-    test('test-mctpd', pytest,
+tests = get_option('tests')
+if tests.allowed()
+    # The test suite contains integration-style tests that we wish to isolate.
+    # The tests drive mctpd's D-Bus interfaces and navigate relevant code paths
+    # by mocking kernel and MCTP device behaviour. The mock behaviours are
+    # implemented by encapsulating netlink and MCTP messages over Unix domain
+    # sockets bound to mock implementations in the test suite.
+    #
+    # Isolate the test suite under its own D-Bus session to prevent test
+    # behaviours impacting applications connected to the usual buses. To
+    # implement the isolation we need to work under some constraints:
+    #
+    # 1. mctpd's implementation connects to a bus by invoking `sd_bus_default()`,
+    #    which uses a combination of environment variables and session
+    #    properties to determine whether to connect to the system bus or the
+    #    session bus
+    #
+    # 2. dbus-run-session configures an isolated session bus and controls the
+    #    relevant environment variables for influencing the application to
+    #    connect to this isolated bus instance.
+    #
+    # `sd_bus_default()` selects the system bus if the application is
+    # not running in a systemd user slice. From experience, in a Github
+    # Action environment the system bus is selected by `sd_bus_default()`,
+    # implying that they aren't exploiting systemd slices. However,
+    # `sd_bus_default()` can be influenced to select the user session by setting
+    # `DBUS_STARTER_BUS_TYPE=user` in the environment. At this point with a
+    # naive approach we run up against 2, where `dbus-run-session` sanitises
+    # that configuration away
+    #
+    # Invoke pytest via a shell script under `dbus-run-session` so we can
+    # override the sanitation of `DBUS_STARTER_BUS_TYPE`, ensuring `test-mctpd`
+    # connects to the isolated session bus prepared by `dbus-run-session`.
+    pytest = find_program('pytest', required: tests)
+    script = 'export DBUS_STARTER_BUS_TYPE=user ; @0@ --tap'.format(pytest.full_path())
+    sh = find_program('sh', required: tests)
+    dbus_run_session = find_program('dbus-run-session', required: tests)
+    test('test-mctpd', dbus_run_session,
         depends: mctpd_test,
-        args: '--tap',
+        args: [ sh.full_path(), '-c', script ],
         protocol: 'tap',
     )
 endif

meson_options.txt

@@ -3,3 +3,4 @@ option('unsafe-writable-connectivity',
        type: 'boolean',
        value: false,
        description: 'Allow writes to the Connectivity member of the au.com.CodeConstruct.MCTP.Endpoint interface on endpoint objects')
+option('tests', type: 'feature')

tests/test-proto.h

@@ -1,9 +1,10 @@
 
 #include <stdint.h>
 
-#include <linux/mctp.h>
 #include <linux/netlink.h>
 
+#include "mctp.h"
+
 enum {
 	CONTROL_OP_INIT,
 	CONTROL_OP_SOCKET_MCTP,