CIFS: Respect epoch value from create lease context v2

that force a client to purge cache pages when a server requests it.

Signed-off-by: Pavel Shilovsky <pshilovsky@samba.org>
Signed-off-by: Steve French <smfrench@gmail.com>
diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 188b247..d044b35 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -323,6 +323,7 @@
 		oplock = fid->pending_open->oplock;
 	list_del(&fid->pending_open->olist);
 
+	fid->purge_cache = false;
 	server->ops->set_fid(cfile, fid, oplock);
 
 	list_add(&cfile->tlist, &tcon->openFileList);
@@ -333,6 +334,9 @@
 		list_add_tail(&cfile->flist, &cinode->openFileList);
 	spin_unlock(&cifs_file_list_lock);
 
+	if (fid->purge_cache)
+		cifs_invalidate_mapping(inode);
+
 	file->private_data = cfile;
 	return cfile;
 }