[CentOS] Where is the kernel source code???

I'd assume

yum --enablerepo centosplus install kernel-devel

:)

> Ok, i installed the kernel from the centosplus repo as you told me but when i 
> try to install nvidia driver(from nvidia), the installer said that it can not 
> find the source file for the kernel in order to build the nvidia module!!! 
> Where can i get the source file for the unsupport kernel?