pNFS/flexfiles: Ensure we initialise the mirror bsizes correctly on read

While it is true that reading from an unmirrored source always uses
index 0, that is no longer true for mirrored sources when we fail over.

Fixes: 563c53e ("NFS: Fix flexfiles read failover")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/flexfilelayout/flexfilelayout.c

@@ -838,6 +838,7 @@ ff_layout_pg_init_read(struct nfs_pageio_descriptor *pgio,
 	struct nfs4_ff_layout_mirror *mirror;
 	struct nfs4_pnfs_ds *ds;
 	int ds_idx;
+	u32 i;
 
 retry:
 	ff_layout_pg_check_layout(pgio, req);
@@ -863,14 +864,14 @@ ff_layout_pg_init_read(struct nfs_pageio_descriptor *pgio,
 		goto retry;
 	}
 
-	mirror = FF_LAYOUT_COMP(pgio->pg_lseg, ds_idx);
+	for (i = 0; i < pgio->pg_mirror_count; i++) {
+		mirror = FF_LAYOUT_COMP(pgio->pg_lseg, i);
+		pgm = &pgio->pg_mirrors[i];
+		pgm->pg_bsize = mirror->mirror_ds->ds_versions[0].rsize;
+	}
 
 	pgio->pg_mirror_idx = ds_idx;
 
-	/* read always uses only one mirror - idx 0 for pgio layer */
-	pgm = &pgio->pg_mirrors[0];
-	pgm->pg_bsize = mirror->mirror_ds->ds_versions[0].rsize;
-
 	if (NFS_SERVER(pgio->pg_inode)->flags &
 			(NFS_MOUNT_SOFT|NFS_MOUNT_SOFTERR))
 		pgio->pg_maxretrans = io_maxretrans;