The relationship between Linux and Android
I have came across the statement that "Android is based on the Linux kernel". So what does it mean?
> is Android a layer on top of the linux kernel? i.e., Does Android actually work in the user space and, if it want to access physical device, it needs to make Linux system call on device nodes such as 'open','read','write'?
> Or Android is actually a modified version of the Linux kernel, so itself works in the kernel space and has direct access to physical devices?
> Or Android is both. i.e., it is a user space layer that manages the apps, and it works on top of a modified version of the Linux kernel?