The was no real rationale except for some people seeing "clone" functionality
as the match and the fact that FS_NAMESCAPE was done so made them believe it is a good way to go.
And I warned about flags limitation at the beginning.
Both OpenVZ/vserver suggested to use a special syscall for handling this.
Maybe it is a good point to switch to it now finally and stop worring about all this?

Andi Kleen wrote:
>> I guess that was a development rationale. 
> 
> But what rationale? It just doesn't make much sense to me.
> 
>> Most of the namespaces are in 
>> use in the container projects like openvz, vserver and probably others 
>> and we needed a way to activate the code.
> 
> You could just have added it to feature groups over time.
> 
>> Not perfect I agree.
>>  
>>> With your current strategy are you sure that even 64bit will
>>> be enough in the end? For me it rather looks like you'll
>>> go through those quickly too as more and more of the kernel
>>> is namespaced.
>> well, we're reaching the end. I hope ! devpts is in progress and
>> mq is just waiting for a clone flag.
> 
> Are you sure?
> 
>>  
>>> Also I think the user interface is very unfriendly. How
>>> is a non kernel hacker supposed to make sense of these 
>>> myriads of flags? You'll be creating another 
>>> CreateProcess123_extra_args_extended() 
>>> in the end I fear.
>> well, the clone interface is a not friendly interface anyway. glibc wraps 
>> it
> 
> But only for the stack setup which is just a minor detail. 
> 
> The basic clone() flags interface used to be pretty sane and usable 
> before it could overloaded with so many tiny features.
> 
> I especially worry on how user land should keep track of changing kernel
> here. If you add new feature flag for lots of kernel features it is
> reasonable to expect that in the future there will be often new features.
> 
> Does this mean user land needs to be updated all the time? Will this
> end up like another udev? 
> 
>> We will need a user library, like we have a libphtread or a libaio, to
> 
> That doesn't make sense. The basic kernel syscalls should be usable,
> not require some magic library that would likely need intimate 
> knowledge of specific kernel versions to do any good.
> 
>> but we still need a way to extend the clone flags because none are left.
> 
> Can we just take out some again that were added in the .25 cycle and
> readd them once there is a properly thought out interface?  That would
> leave at least one.
> 
> -Andi
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