Confusion on alternatives for /usr/lib/xorg/modules/linux/libglx.so

[Hualet Wang]

Hi, Debian NVIDIA Maintainers 

Recently I’m trying port nvidia-prime to our distribution, deepin which is a Debian Sid derivative, during the process I found that users with nvidia-dirver installed, some of them got /usr/lib/xorg/modules/linux/libglx.so and some of them didn’t, and among the users who got /usr/lib/xorg/modules/linux/libglx.so, some of their X load that file when LoadModule glx happens, and the others just load /usr/lib/xorg/modules/extensions/libglx.so.

I checked postinst script of glx-alternative-nvidia, and see it "handles alternatives for /usr/lib/xorg/modules/linux/libglx.so”.

So I’m totally confused:
[1] why there’s an alternatives for /usr/lib/xorg/modules/linux/libglx.so ? 
[2] how the nvidia-driver suppose to change the behavior that which libglx.so is loaded ?

I can’t find any useful information on the Internet, can you help me with that ? 
Any guidance would be greatly appreaciated.

Best reguards, Hualet.