Added to vendor

vendor/github.com/containers/storage/lockfile.go

@@ -0,0 +1,82 @@
+package storage
+
+import (
+	"fmt"
+	"path/filepath"
+	"sync"
+	"time"
+
+	"github.com/pkg/errors"
+)
+
+// A Locker represents a file lock where the file is used to cache an
+// identifier of the last party that made changes to whatever's being protected
+// by the lock.
+type Locker interface {
+	sync.Locker
+
+	// Touch records, for others sharing the lock, that the caller was the
+	// last writer.  It should only be called with the lock held.
+	Touch() error
+
+	// Modified() checks if the most recent writer was a party other than the
+	// last recorded writer.  It should only be called with the lock held.
+	Modified() (bool, error)
+
+	// TouchedSince() checks if the most recent writer modified the file (likely using Touch()) after the specified time.
+	TouchedSince(when time.Time) bool
+
+	// IsReadWrite() checks if the lock file is read-write
+	IsReadWrite() bool
+}
+
+var (
+	lockfiles     map[string]Locker
+	lockfilesLock sync.Mutex
+)
+
+// GetLockfile opens a read-write lock file, creating it if necessary.  The
+// Locker object it returns will be returned unlocked.
+func GetLockfile(path string) (Locker, error) {
+	lockfilesLock.Lock()
+	defer lockfilesLock.Unlock()
+	if lockfiles == nil {
+		lockfiles = make(map[string]Locker)
+	}
+	cleanPath := filepath.Clean(path)
+	if locker, ok := lockfiles[cleanPath]; ok {
+		if !locker.IsReadWrite() {
+			return nil, errors.Wrapf(ErrLockReadOnly, "lock %q is a read-only lock", cleanPath)
+		}
+		return locker, nil
+	}
+	locker, err := getLockFile(path, false) // platform dependent locker
+	if err != nil {
+		return nil, err
+	}
+	lockfiles[filepath.Clean(path)] = locker
+	return locker, nil
+}
+
+// GetROLockfile opens a read-only lock file.  The Locker object it returns
+// will be returned unlocked.
+func GetROLockfile(path string) (Locker, error) {
+	lockfilesLock.Lock()
+	defer lockfilesLock.Unlock()
+	if lockfiles == nil {
+		lockfiles = make(map[string]Locker)
+	}
+	cleanPath := filepath.Clean(path)
+	if locker, ok := lockfiles[cleanPath]; ok {
+		if locker.IsReadWrite() {
+			return nil, fmt.Errorf("lock %q is a read-write lock", cleanPath)
+		}
+		return locker, nil
+	}
+	locker, err := getLockFile(path, true) // platform dependent locker
+	if err != nil {
+		return nil, err
+	}
+	lockfiles[filepath.Clean(path)] = locker
+	return locker, nil
+}