How to define the label of boundary(3D cylinder with hole)


I have question towards 3d mesh.
I want to build a mesh of 3d cylinder with a hole. So I build a 2d mesh of the circle with a hole first and then use buildlayers() to expand it to 3d.

how to define the label of boundary?

Here is my code.

load “msh3”
load “medit”
load “tetgen”
//Builds a mesh on 3d cylinder with a hole.
real cx1 = 0.0;
real cy1 = 0.0;
real r1 = 1.0;
real cx2 = 0.5;
real cy2 = 0.0;
real r2 = 0.1;
real zmin=0,zmax=1;
int[int] rup=[0,1], rdown=[0,2], rmid=[1,3];
border C1(t1=0,2pi){x=cx1+r1cos(t1);y=cy1+r1sin(t1);};
border C2(t1=0,2

int m=5;
mesh Thcercle = buildmesh(C1(4*m)+C2(-m));
//plot(Thcercle,wait =1);

mesh3 ThF=buildlayers(Thcercle,
labelup = rup,
labeldown = rdown);