ext2fs superblock updates

[coypu%sdf.org@localhost]

Hi folks.

From the looks of it, the ext2fs code only updates the primary
superblock:

/*
 * Write a superblock and associated information back to disk.
 */
int
ext2fs_sbupdate(struct ufsmount *mp, int waitfor)
{
        struct m_ext2fs *fs = mp->um_e2fs;
        struct buf *bp;
        int error = 0;

        bp = getblk(mp->um_devvp, SBLOCK, SBSIZE, 0, 0);
        e2fs_sbsave(&fs->e2fs, (struct ext2fs*)bp->b_data);
        if (waitfor == MNT_WAIT)
                error = bwrite(bp);
        else
                bawrite(bp);
        return error;
}

I'm under the impression that the secondary ones exist as
backups and are meant to be usable.

Is this wrong or am I misunderstanding things?

Thanks.