virtcontainers: Initial Store implementation

Store is a replacement for the current resource storage virtcontainers
implementation and the Manager is the front-end for it. The back-ends
will provide actual storage capabilities and the first one will be the
filesystem one, for storing virtcontainers Items on a local filesystem.

The main design goals for Store are the following ones:

- Simplicity: The API should be short and simple.
- Transparency: The core virtcontainers code should not care about
  the storage backend details.
- Extensibility: It should be easily extensible to add non local and in
  memory backends.

Manger provides a very short and simple API for the rest of the virtcontainers
code base to consume:

New: Creates a new Store, if needed.
Load: Loads an Item from a Store
Store: Stores an Item into a Store.

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

virtcontainers/store/manager.go

@@ -0,0 +1,156 @@
+// Copyright (c) 2019 Intel Corporation
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+package store
+
+import (
+	"context"
+	"net/url"
+	"sync"
+
+	opentracing "github.com/opentracing/opentracing-go"
+	"github.com/sirupsen/logrus"
+)
+
+// Item represents a virtcontainers items that will be managed through the store.
+type Item uint8
+
+const (
+	// Configuration represents a configuration item to be stored
+	Configuration Item = iota
+
+	// State represents a state item to be stored.
+	State
+
+	// Network represents a networking item to be stored.
+	Network
+
+	// Hypervisor represents an hypervisor item to be stored.
+	Hypervisor
+
+	// Agent represents a agent item to be stored.
+	Agent
+
+	// Process represents a container process item to be stored.
+	Process
+
+	// Lock represents a lock item to be stored.
+	Lock
+
+	// Mounts represents a set of mounts related item to be stored.
+	Mounts
+
+	// Devices represents a set of devices related item to be stored.
+	Devices
+
+	// DeviceIDs represents a set of reference IDs item to be stored.
+	DeviceIDs
+)
+
+func (i Item) String() string {
+	switch i {
+	case Configuration:
+		return "Configuration"
+	case State:
+		return "State"
+	case Network:
+		return "Network"
+	case Hypervisor:
+		return "Hypervisor"
+	case Agent:
+		return "Agent"
+	case Process:
+		return "Process"
+	case Lock:
+		return "Lock"
+	case Mounts:
+		return "Mounts"
+	case Devices:
+		return "Devices"
+	case DeviceIDs:
+		return "Device IDs"
+	}
+
+	return ""
+}
+
+// Store is an opaque structure representing a virtcontainers Store.
+type Store struct {
+	sync.RWMutex
+	ctx context.Context
+
+	url    string
+	scheme string
+	path   string
+	host   string
+}
+
+// New will return a new virtcontainers Store.
+// If there is already a Store for the URL, we will re-use it.
+// Otherwise a new Store is created.
+func New(ctx context.Context, storeURL string) (*Store, error) {
+	u, err := url.Parse(storeURL)
+	if err != nil {
+		return nil, err
+	}
+
+	return &Store{
+		ctx:    ctx,
+		url:    storeURL,
+		scheme: u.Scheme,
+		path:   u.Path,
+		host:   u.Host,
+	}, nil
+}
+
+var storeLog = logrus.WithField("source", "virtcontainers/store")
+
+// Logger returns a logrus logger appropriate for logging Store messages
+func (s *Store) Logger() *logrus.Entry {
+	return storeLog.WithFields(logrus.Fields{
+		"subsystem": "store",
+		"path":      s.path,
+	})
+}
+
+func (s *Store) trace(name string) (opentracing.Span, context.Context) {
+	if s.ctx == nil {
+		s.Logger().WithField("type", "bug").Error("trace called before context set")
+		s.ctx = context.Background()
+	}
+
+	span, ctx := opentracing.StartSpanFromContext(s.ctx, name)
+
+	span.SetTag("subsystem", "store")
+	span.SetTag("path", s.path)
+
+	return span, ctx
+}
+
+// Load loads a virtcontainers item from a Store.
+func (s *Store) Load(item Item, data interface{}) error {
+	span, _ := s.trace("Load")
+	defer span.Finish()
+
+	span.SetTag("item", item)
+
+	s.RLock()
+	defer s.RUnlock()
+
+	return nil
+}
+
+// Store stores a virtcontainers item into a Store.
+func (s *Store) Store(item Item, data interface{}) error {
+	span, _ := s.trace("Store")
+	defer span.Finish()
+
+	span.SetTag("item", item)
+
+	s.Lock()
+	defer s.Unlock()
+
+	return nil
+}

virtcontainers/store/manager_test.go

@@ -0,0 +1,21 @@
+// Copyright (c) 2019 Intel Corporation
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+package store
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestNewStore(t *testing.T) {
+	s, err := New(context.Background(), "file:///root/")
+	assert.Nil(t, err)
+	assert.Equal(t, s.scheme, "file")
+	assert.Equal(t, s.host, "")
+	assert.Equal(t, s.path, "/root/")
+}