What's in include/uapi of kernel source project

Question

Can someone please give me a document to describe the kernel source folders about their structure, functionality and how they are organized?

Specifically, what's the use of of the folder include/uapi/**?

Thanks.

Answer 1

The uapi folder is supposed to contain the user space API of the kernel. Then upon kernel installation, the uapi include files become the top level /usr/include/linux/ files. (I'm not entirely clear on what exceptions remain.)

The other headers in theory are then private to the kernel. This allow clean separation of the user-visible and kernel-only structures which previously were intermingled in a single header file.

The best discussion I have seen of this is located at a Linux Weekly News article that predates the patch landing.

The UAPI patch itself landed with kernel 3.7. Linus's quick and dirty summary is:

• the "uapi" include file cleanups. The idea is that the stuff exported to user space should now be found under include/uapi and arch/$(ARCH)/include/uapi.

  Let's hope it actually works. Because otherwise this was just a totally pointless pain in the *ss. And regardless, I'm definitely done with these kinds of "let's do massive cleanup of the include files" forever.