Hi All,
Do you have any suggestions on good complete development or at least best up to date latest book for OpenWrt development ?
Any suggestion or recommendation would be helpful.
Thanks in advance!
I would appreciate this, too. But realistically, no chance. As lots of info very well hidden, almost secret, only to be documented in form of "C-Code" or shell scripts. An example is procd, or ubus.
It is common practice for open source development, that documentation is almost non-existant.
As coding makes mor fun than writing some docs.
I remember my early days of coding, when almost every line of Assembler code had a comment, or every function (we called it subroutine) had some well defined header comments, incl. description of input and output. Of course, there were docs like "Principles of Operation" (the "WHAT to be done") or "User Manual" (how to use the API) for mayor function blocks.
These days are long gone.
that completely true for current open source development where focus is on development which may get outdated with new idea and documentation too quickly become outdated.
I am quite use to with that but sometime its good to get overall idea to get code intention - it just make code reading bit faster or even quicker to start modifying it as per need. But definitely code is all most of the time what can tell everything about utility or application 
You could try using something like Doxygen on the source and generate some documentation form the source code itself.
I can hardly see any doxygen comment to generate doxygen documentation.
Yocto has that plus over OpenWrt but then that's just way hard to pick up because of its make system (poky...) and tool settings.
OpenWrt is way easy as per my finding in that but just get hard to make changes - currently I focus on LuCI RPC and rpcd for setting restricted user with limited RPC calls and I am going on ....
you could search for "openwrt pdf" on maybe a search for "openwrt" and add a particular piece of hardware