ceph: use __getname/__putname in ceph_mdsc_build_path

Al suggested we get rid of the kmalloc here and just use __getname
and __putname to get a full PATH_MAX pathname buffer.

Since we build the path in reverse, we continue to return a pointer
to the beginning of the string and the length, and add a new helper
to free the thing at the end.

Suggested-by: Al Viro <[email protected]>
Signed-off-by: Jeff Layton <[email protected]>
Reviewed-by: "Yan, Zheng" <[email protected]>
Signed-off-by: Ilya Dryomov <[email protected]>
diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h
index 0d1f673..ebcad5af 100644
--- a/fs/ceph/mds_client.h
+++ b/fs/ceph/mds_client.h
@@ -492,6 +492,12 @@ extern int ceph_iterate_session_caps(struct ceph_mds_session *session,
 				     void *arg);
 extern void ceph_mdsc_pre_umount(struct ceph_mds_client *mdsc);
 
+static inline void ceph_mdsc_free_path(char *path, int len)
+{
+	if (path)
+		__putname(path - (PATH_MAX - 1 - len));
+}
+
 extern char *ceph_mdsc_build_path(struct dentry *dentry, int *plen, u64 *base,
 				  int stop_on_nosnap);