State of userland headers

[Kyle Moffett]

On Mar 24, 2006, at 20:36:15, Jeff Dike wrote:
> On Fri, Mar 24, 2006 at 05:46:27PM -0500, Kyle Moffett wrote:
>> 4)  UML runs into a lot of problems when glibc's headers and the
>> native kernel headers headers conflict.
>>
>> UML has other issues with conflicts between the native kernel  
>> headers and the GLIBC-provided stubs.  It's been mentioned on the  
>> prior threads about this topic that this sort of system would ease  
>> most of the issues that UML runs into.
>
> Actually, this isn't quite the same as what UML hits.  My problem  
> with the kernel headers is that they are a mixture of things that  
> are usable in userspace and things that aren't.  This is closely  
> related, but not identical to, things which are part of the ABI and  
> things which aren't.
>
> For example, the kernel locks are quite usable in userspace, but  
> you would never make them part of the ABI.
>
> So, a set of KABI headers would likely make UML's headers cleaner,  
> by avoiding copying arch headers and using various nasty tricks to  
> disable objectionable pieces of headers which I steal from the arch.
>
> So what I really want is a superset of the KABI headers, but the  
> KABI will give me most of what I want.

So perhaps could we define an informal subset of the kernel code that  
works in both userspace and kernel-space and put it in include/libk?   
Stuff like linked lists, spinlocks (depends on arch, may not be  
supported), etc could be in linux/libk and linux/include/libk or  
similar, and then from there included into linux/include/linux/ 
list.h, etc, as well as into the UML files that need it.  Since the  
provider and user would both be the Linux kernel, I see no issues  
with trying to provide a stable interface of any kind, especially if  
we document it as "PRIVATE - FOR KERNEL USE ONLY!!!" with big warning  
signs. As a nice bonus, this would make it possible to implement some  
user-space unit tests of various pieces.

Cheers,
Kyle Moffett