virtcontainers: fs_share: add Darwin skeleton

Fixes: #6002

As a first pass for testing, let's add a skeleton for filesystem
sharing support on Darwin..

Signed-off-by: Eric Ernst <eric_ernst@apple.com>
Signed-off-by: Danny Canter <danny@dcantah.dev>

src/runtime/virtcontainers/fs_share_darwin.go

@@ -0,0 +1,58 @@
+// Copyright (c) 2023 Apple Inc.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+package virtcontainers
+
+import (
+	"context"
+	"sync"
+
+	"github.com/sirupsen/logrus"
+)
+
+type FilesystemShare struct {
+	sandbox *Sandbox
+	sync.Mutex
+	prepared bool
+}
+
+func NewFilesystemShare(s *Sandbox) (FilesystemSharer, error) {
+	return &FilesystemShare{
+		prepared: false,
+		sandbox:  s,
+	}, nil
+}
+
+// Logger returns a logrus logger appropriate for logging Filesystem sharing messages
+func (f *FilesystemShare) Logger() *logrus.Entry {
+	return virtLog.WithFields(logrus.Fields{
+		"subsystem": "filesystem share",
+		"sandbox":   f.sandbox.ID(),
+	})
+}
+
+func (f *FilesystemShare) Prepare(ctx context.Context) error {
+	return nil
+}
+
+func (f *FilesystemShare) Cleanup(ctx context.Context) error {
+	return nil
+}
+
+func (f *FilesystemShare) ShareFile(ctx context.Context, c *Container, m *Mount) (*SharedFile, error) {
+	return nil, nil
+}
+
+func (f *FilesystemShare) UnshareFile(ctx context.Context, c *Container, m *Mount) error {
+	return nil
+}
+
+func (f *FilesystemShare) ShareRootFilesystem(ctx context.Context, c *Container) (*SharedFile, error) {
+	return nil, nil
+}
+
+func (f *FilesystemShare) UnshareRootFilesystem(ctx context.Context, c *Container) error {
+	return nil
+}