Two questions about Emacs gtags mode

[Water Lin <WaterLin@ymail.invalid>]

1. My Emacs can't find tags

I am trying to use Gtags mode in my Emacs to read source code. In my
project folder, I use cammad $ gtags from shell to establish four
necessary files like GPATH, GTAGS.

I also use command $ gtags to establish index in my /usr/include folder,
and I also add /usr/include to environment variable GTAGSLIBPATH. So now
I can use command

$ global timeval

, and I will get output like:
-----------
$ global timeval
../../../../../../usr/include/X11/Xos.h
../../../../../../usr/include/audio/Aos.h
../../../../../../usr/include/bits/time.h
../../../../../../usr/include/linux/time.h
-----------

It seems that global works all right now.

But when I use Emacs gtags-mode, I use M-. to check the declaration of

timeval

, Emacs prompts me that "timeval: tag not found [2 times]".

Why my Emacs can't find this tag?

2. What is the difference between the Google-gtags and Emacs default
gtags-mode? The Google-gtags link is:
-----------
http://code.google.com/p/google-gtags/
-----------

Hope someone can help me!

Thanks

Water Lin
-- 
Water Lin's notes and pencils: http://en.waterlin.org
Email: WaterLin@ymail.com