fsmonitor: Test unix devices with both drivers (canonical#14111)

The `fsmonitor` package has two drivers, but only fanotify is tested for
unix devices (see
canonical#14110 (comment)).
This is the default driver but it may not be available in all
kernels/architectures.

This PR adds an environment variable to force a specific driver to be
used. The unix char and block device tests are then run with both
drivers.

The `inotify` package was encountering some unknown events. As it turned
out, mapping these events to `fsmonitor` events broke the test suite, so
I've added exceptions for them to reduce log verbosity.

doc/environment.md

@@ -40,3 +40,4 @@ Name                            | Description
 `LXD_QEMU_FW_PATH`              | Path (or `:` separated list of paths) to firmware (OVMF, SeaBIOS) to be used by QEMU
 `LXD_IDMAPPED_MOUNTS_DISABLE`   | Disable idmapped mounts support (useful when testing traditional UID shifting)
 `LXD_DEVMONITOR_DIR`            | Path to be monitored by the device monitor. This is primarily for testing.
+`LXD_FSMONITOR_DRIVER`          | Driver to be used for file system monitoring. This is primarily for testing.

lxd/fsmonitor/drivers/driver_inotify.go

@@ -36,13 +36,19 @@ var fsMonitorEventToINotifyEvent = map[fsmonitor.Event]uint32{
 	fsmonitor.EventRename: in.InMovedTo,
 }
 
+var errIgnoreEvent = errors.New("Intentionally ignored event")
+
 func (d *inotify) toFSMonitorEvent(mask uint32) (fsmonitor.Event, error) {
 	for knownINotifyEvent, event := range inotifyEventToFSMonitorEvent {
 		if mask&knownINotifyEvent != 0 {
 			return event, nil
 		}
 	}
 
+	if mask&in.InIgnored != 0 || mask&(in.InUnmount|in.InIsdir) != 0 {
+		return -1, errIgnoreEvent
+	}
+
 	return -1, fmt.Errorf(`Unknown inotify event "%d"`, mask)
 }
 
@@ -102,7 +108,10 @@ func (d *inotify) getEvents(ctx context.Context) {
 			event.Name = filepath.Clean(event.Name)
 			action, err := d.toFSMonitorEvent(event.Mask)
 			if err != nil {
-				logger.Warn("Failed to match inotify event, skipping", logger.Ctx{"err": err})
+				if !errors.Is(err, errIgnoreEvent) {
+					logger.Warn("Failed to match inotify event, skipping", logger.Ctx{"err": err})
+				}
+
 				continue
 			}
 

lxd/fsmonitor/drivers/load.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"os"
 
 	"github.com/canonical/lxd/lxd/fsmonitor"
 	"github.com/canonical/lxd/shared/logger"
@@ -40,6 +41,11 @@ func Load(ctx context.Context, path string, events ...fsmonitor.Event) (fsmonito
 		return d, nil
 	}
 
+	driverName := os.Getenv("LXD_FSMONITOR_DRIVER")
+	if driverName != "" {
+		return startMonitor(driverName)
+	}
+
 	driver, err := startMonitor("fanotify")
 	if err != nil {
 		logger.Warn("Failed to initialize fanotify, falling back on inotify", logger.Ctx{"err": err})

test/suites/container_devices_unix.sh

@@ -1,9 +1,37 @@
 test_container_devices_unix_block() {
+  lxdFSMonitorDriver=${LXD_FSMONITOR_DRIVER:-}
+
+  shutdown_lxd "${LXD_DIR}"
+  export LXD_FSMONITOR_DRIVER="fanotify"
+  respawn_lxd "${LXD_DIR}" true
+  _container_devices_unix "unix-block"
+
+  shutdown_lxd "${LXD_DIR}"
+  export LXD_FSMONITOR_DRIVER="inotify"
+  respawn_lxd "${LXD_DIR}" true
   _container_devices_unix "unix-block"
+
+  shutdown_lxd "${LXD_DIR}"
+  export LXD_FSMONITOR_DRIVER="${lxdFSMonitorDriver}"
+  respawn_lxd "${LXD_DIR}" true
 }
 
 test_container_devices_unix_char() {
+  lxdFSMonitorDriver=${LXD_FSMONITOR_DRIVER:-}
+
+  shutdown_lxd "${LXD_DIR}"
+  export LXD_FSMONITOR_DRIVER="fanotify"
+  respawn_lxd "${LXD_DIR}" true
+  _container_devices_unix "unix-char"
+
+  shutdown_lxd "${LXD_DIR}"
+  export LXD_FSMONITOR_DRIVER="inotify"
+  respawn_lxd "${LXD_DIR}" true
   _container_devices_unix "unix-char"
+
+  shutdown_lxd "${LXD_DIR}"
+  export LXD_FSMONITOR_DRIVER="${lxdFSMonitorDriver}"
+  respawn_lxd "${LXD_DIR}" true
 }
 
 _container_devices_unix() {