[LU-14177] PCC: Invalidate PCC-RO cache when access from the old client

• Type: Technical task
• Resolution: Unresolved
• Priority: Minor
• Assignee: Qian Yingjin
• Reporter: Qian Yingjin

Description

For the purpose of the compatibility and interoperability, we have already added a PCC-RO connection flag;
To avoid inconsistent data access, MDT does not (try to) grant layout lock to the client at the time of getattr() or open(). when an old client without PCC-RO support requests a layout lock via intent request on the file that is in L.rdonly state on MDT, MDT needs to clear the L.rdonly flag on the layout first (this maybe invalidate all PCC-RO cached copies on clients), and then return the layout to the old client.