ceph: fix st_nlink stat for directories

Currently, calling stat on a cephfs directory returns 1 for st_nlink.
This behaviour has recently changed in the fuse client, as some
applications seem to expect this value to be either 0 (if it's
unlinked) or 2 + number of subdirectories.  This behaviour was changed
in the fuse client with commit 67c7e4619188 ("client: use common
interp of st_nlink for dirs").

This patch modifies the kernel client to have a similar behaviour.

Link: https://tracker.ceph.com/issues/23873
Signed-off-by: Luis Henriques <lhenriques@suse.com>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/inode.c

@@ -2271,6 +2271,14 @@ int ceph_getattr(const struct path *path, struct kstat *stat,
 				stat->size = ci->i_files + ci->i_subdirs;
 			stat->blocks = 0;
 			stat->blksize = 65536;
+			/*
+			 * Some applications rely on the number of st_nlink
+			 * value on directories to be either 0 (if unlinked)
+			 * or 2 + number of subdirectories.
+			 */
+			if (stat->nlink == 1)
+				/* '.' + '..' + subdirs */
+				stat->nlink = 1 + 1 + ci->i_subdirs;
 		}
 	}
 	return err;