Linux kernel headers' organization

Question

While I was doing some reading on system calls, I did a search for syscalls.h to find the header file in LXR. The search results puzzled me. There is a dozen of syscalls.h files coming from directories under arch/_arch_name_/include/asm. These are ok, they are architecture specific definitions or something else needed. The question is why do we have two different syscalls.h headers under both include/linux and include/asm-generic?

Also, I want to find out that what include/linux headers are for and what include/asm-generic headers are for. How do they differentiate between each other? What is the logic behind having two separate header folders? How do they relate to each other?

Thanks

Answer 1

I've asked this question on Kernel Newbies ML. I got the following answer which makes things clear:

Cihangir Akturk wrote:

AFAIK, headers found in /include/asm-generic directory is for architechture independent (probably shared across architectures) code. Most likely you do not need to include these headers directly, instead we include these headers indirectly via architecthure dependent headers.

OTOH, /include/linux directory is for generic header files to define interfaces between components of the kernel. In most situations, you will find all the kernel functionalities you need in these headers.

regards, chngr.