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

Tejun Heo teheo at suse.de
Mon Jul 30 00:09:06 PDT 2007

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.


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