Trying to mount nfs share on openwrt

Hi. I'm trying to mount an external nfs share in openwrt, but when I run:

mount -t nfs /mnt/tmp -o nolock

I get "No such device" error. The same command mounts succesfully the share in an ubuntu machine.
I installed kmod-fs-nfs-common, kmod-fs-nfs-common-rpcsec, kmod-fs-nfsd, nfs-utils and nfs-utils-libs packages. I think that the correct modules are loaded:

root@OpenWrt:/# lsmod | grep nfs
auth_rpcgss            57344  2 nfsd,rpcsec_gss_krb5
grace                  16384  2 nfsd,lockd
lockd                  73728  1 nfsd
nfsd                  294912  0 
sunrpc                237568  4 nfsd,rpcsec_gss_krb5,auth_rpcgss,lockd

What is happening?. Any help would be appreciated. Thanks

EDIT: forgot to tell I am using current snapshot build in EA8500.

Hi. Already did all the steps in that guide prior of writing here. In fact most of the packages shown there do not exist anymore:

root@OpenWrt:~# opkg install nfs-utils kmod-fs-nfs kmod-fs-nfs-v4 kmod-fs-nfs-v3
Package nfs-utils (2.5.4-4) installed in root is up to date.
Unknown package 'kmod-fs-nfs'.
Unknown package 'kmod-fs-nfs-v4'.
Unknown package 'kmod-fs-nfs-v3'.
Collected errors:
 * opkg_install_cmd: Cannot install package kmod-fs-nfs.
 * opkg_install_cmd: Cannot install package kmod-fs-nfs-v4.
 * opkg_install_cmd: Cannot install package kmod-fs-nfs-v3

Those packages do exist for the 5.4 kernel...

Run opkg update first.