ceph: don't request excl caps when mount is readonly

Signed-off-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/caps.c

@@ -1855,14 +1855,17 @@ retry_locked:
 			retain |= CEPH_CAP_ANY;       /* be greedy */
 		} else if (S_ISDIR(inode->i_mode) &&
 			   (issued & CEPH_CAP_FILE_SHARED) &&
-			    __ceph_dir_is_complete(ci)) {
+			   __ceph_dir_is_complete(ci)) {
 			/*
 			 * If a directory is complete, we want to keep
 			 * the exclusive cap. So that MDS does not end up
 			 * revoking the shared cap on every create/unlink
 			 * operation.
 			 */
-			want = CEPH_CAP_ANY_SHARED | CEPH_CAP_FILE_EXCL;
+			if (IS_RDONLY(inode))
+				want = CEPH_CAP_ANY_SHARED;
+			else
+				want = CEPH_CAP_ANY_SHARED | CEPH_CAP_FILE_EXCL;
 			retain |= want;
 		} else {