sv_forw
wsp->walk_addr = (uintptr_t)sn.sv_forw;
svp->sv_forw = svp->sv_back = svp;
svp->sv_forw = svp->sv_back = svp;
for (svp = master_svp->sv_forw; svp != master_svp; svp = svp->sv_forw)
svp->sv_forw = svp->sv_back = NULL;
for (svp = rp->r_svnode.sv_forw; svp != &rp->r_svnode;
svp = svp->sv_forw)