virtcontainers: store: Add a ItemLock API

The ItemLock API allows for taking shared and exclusive locks on all
items.
For virtcontainers, this is specialized into taking locks on the Lock
item, and will be used for sandbox locking.

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

virtcontainers/store/vc.go

@@ -202,6 +202,21 @@ func (s *VCStore) Raw(id string) (string, error) {
 	return s.state.Raw(id)
 }
 
+// Lock takes an exclusive lock on the virtcontainers state Lock item.
+func (s *VCStore) Lock() (string, error) {
+	return s.state.ItemLock(Lock, true)
+}
+
+// RLock takes a shared lock on the virtcontainers state Lock item.
+func (s *VCStore) RLock() (string, error) {
+	return s.state.ItemLock(Lock, false)
+}
+
+// Unlock unlocks the virtcontainers state Lock item.
+func (s *VCStore) Unlock(token string) error {
+	return s.state.ItemUnlock(Lock, token)
+}
+
 // Utilities for virtcontainers
 
 // SandboxConfigurationRoot returns a virtcontainers sandbox configuration root URL.