p9fs_get_open_fid
error = p9fs_get_open_fid(vp, FREAD, ap->a_cred, &ostate);
error = p9fs_get_open_fid(vp, FWRITE, ap->a_cred, &ostate);
error = p9fs_get_open_fid(vp, bp->b_iocmd == BIO_READ ? FREAD : FWRITE, cr, &ostate);