Add a Filter interface to the discover package

This change adds support for filtering entities by specifying a filter.
This can be used, for example, to check whether a mount or device
has a particular property and removing it from the set of discovered
entities if it does not.

Signed-off-by: Evan Lezar <elezar@nvidia.com>

internal/discover/filter.go

@@ -0,0 +1,53 @@
+/**
+# Copyright (c) 2022, NVIDIA CORPORATION.  All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+**/
+
+package discover
+
+import "github.com/sirupsen/logrus"
+
+// Filter defines an interface for filtering discovered entities
+type Filter interface {
+	DeviceIsSelected(device Device) bool
+}
+
+// filtered represents a filtered discoverer
+type filtered struct {
+	Discover
+	logger *logrus.Logger
+	filter Filter
+}
+
+// Devices returns a filtered list of devices based on the specified filter.
+func (d filtered) Devices() ([]Device, error) {
+	devices, err := d.Discover.Devices()
+	if err != nil {
+		return nil, err
+	}
+
+	if d.filter == nil {
+		return devices, nil
+	}
+
+	var selected []Device
+	for _, device := range devices {
+		if d.filter.DeviceIsSelected(device) {
+			selected = append(selected, device)
+		}
+		d.logger.Debugf("skipping device %v", device)
+	}
+
+	return selected, nil
+}