Return EEXIST from create. This appears to work, on OS X at least.

errors.go

@@ -23,6 +23,7 @@ import (
 const (
 	// Errors corresponding to kernel error numbers. These may be treated
 	// specially by fuseops.Op.Respond methods.
+	EEXIST    = bazilfuse.EEXIST
 	EINVAL    = bazilfuse.Errno(syscall.EINVAL)
 	EIO       = bazilfuse.EIO
 	ENOENT    = bazilfuse.ENOENT

samples/memfs/memfs.go

@@ -345,7 +345,7 @@ func (fs *memFS) CreateFile(
 	// duplicate.
 	_, exists := parent.LookUpChild(op.Name)
 	if exists {
-		err = fmt.Errorf("Name %q already exists in parent", op.Name)
+		err = fuse.EEXIST
 		return
 	}