[Devel] Re: [PATCH 2/4] sysfs: Implement sysfs manged shadow directory support.

[Kirill Korotaev]

Tejun Heo wrote:
> Hello, Eric.
> 
> Tejun Heo wrote:
> 
>>Eric W. Biederman wrote:
>>
>>>Further while there are a few little nits I think mostly Tejun is 
>>>mostly objecting to the fundamental complexity of the problem rather
>>>then to things that can be fixed by a cleaner implementation.
>>
>>Oh well, I don't think so but I might be wrong.
> 
> 
> And I'm wrong.  Mine didn't turn out to be much cleaner than yours.
> What I did was (still broken)...
> 
> * No shadower/shadowee.  Each dentry is tagged.
> * dentries of tagged sd's are taken out of dcache and always go through
> ->lookup() where the correct sd is looked up considering the current tag.
> 
> Tagging and adding new entries could be done rather cleanly but shooting
> down existing dentries on rename/move turned out to be a mess.  Things
> will be much simpler if no sysfs dentry is hashed on dcache and always
> go through ->lookup() but that will hurt big machines.
> 
> The basic problem here is that dcache layer doesn't allow different
> views and sysfs shadow is trying to work behind its back.  I don't think
> this is a viable approach.  Both implementations bend too many rules and
>  are too fragile.  It will be a genuine pain in the ass to maintain.
> 
> Sorry that I can't come up with an alternative but NACK.

Imho then OpenOVZ approach with multiple sysfs trees is better.
it allows to use cached dentries with moultiple sysfs mounts
each having different view.
It also allows to hide hw-related entries and events from the containers
and has quite little modifications in the code.

Thanks,
Kirill

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