nfsd: clean up mounted_on_fileid handling

We only need the inode number for this, not a full rack of attributes.
Rename this function make it take a pointer to a u64 instead of
struct kstat, and change it to just request STATX_INO.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
[ cel: renamed get_mounted_on_ino() ]
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfs4xdr.c

@@ -2769,18 +2769,21 @@ static __be32 fattr_handle_absent_fs(u32 *bmval0, u32 *bmval1, u32 *bmval2, u32
 }
 
 
-static int get_parent_attributes(struct svc_export *exp, struct kstat *stat)
+static int nfsd4_get_mounted_on_ino(struct svc_export *exp, u64 *pino)
 {
 	struct path path = exp->ex_path;
+	struct kstat stat;
 	int err;
 
 	path_get(&path);
 	while (follow_up(&path)) {
 		if (path.dentry != path.mnt->mnt_root)
 			break;
 	}
-	err = vfs_getattr(&path, stat, STATX_BASIC_STATS, AT_STATX_SYNC_AS_STAT);
+	err = vfs_getattr(&path, &stat, STATX_INO, AT_STATX_SYNC_AS_STAT);
 	path_put(&path);
+	if (!err)
+		*pino = stat.ino;
 	return err;
 }
 
@@ -3277,22 +3280,21 @@ nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc_fh *fhp,
 		*p++ = cpu_to_be32(stat.btime.tv_nsec);
 	}
 	if (bmval1 & FATTR4_WORD1_MOUNTED_ON_FILEID) {
-		struct kstat parent_stat;
 		u64 ino = stat.ino;
 
 		p = xdr_reserve_space(xdr, 8);
 		if (!p)
                 	goto out_resource;
 		/*
-		 * Get parent's attributes if not ignoring crossmount
-		 * and this is the root of a cross-mounted filesystem.
+		 * Get ino of mountpoint in parent filesystem, if not ignoring
+		 * crossmount and this is the root of a cross-mounted
+		 * filesystem.
 		 */
 		if (ignore_crossmnt == 0 &&
 		    dentry == exp->ex_path.mnt->mnt_root) {
-			err = get_parent_attributes(exp, &parent_stat);
+			err = nfsd4_get_mounted_on_ino(exp, &ino);
 			if (err)
 				goto out_nfserr;
-			ino = parent_stat.ino;
 		}
 		p = xdr_encode_hyper(p, ino);
 	}