[Devel] Re: [PATCH] fix bad behavior in use_hierarchy file

[Glauber Costa]

On 06/26/2012 12:49 AM, Tejun Heo wrote:
> On Mon, Jun 25, 2012 at 01:21:01PM +0400, Glauber Costa wrote:
>> I have an application that does the following:
>>
>> * copy the state of all controllers attached to a hierarchy
>> * replicate it as a child of the current level.
>>
>> I would expect writes to the files to mostly succeed, since they
>> are inheriting sane values from parents.
>>
>> But that is not the case for use_hierarchy. If it is set to 0, we
>> succeed ok. If we're set to 1, the value of the file is automatically
>> set to 1 in the children, but if userspace tries to write the
>> very same 1, it will fail. That same situation happens if we
>> set use_hierarchy, create a child, and then try to write 1 again.
>>
>> Now, there is no reason whatsoever for failing to write a value
>> that is already there. It doesn't even match the comments, that
>> states:
>>
>>   /* If parent's use_hierarchy is set, we can't make any modifications
>>    * in the child subtrees...
>>
>> since we are not changing anything.
>>
>> The following patch tests the new value against the one we're storing,
>> and automatically return 0 if we're not proposing a change.
>
> A bit of delta but is there any chance we can either deprecate
> .use_hierarhcy or at least make it global toggle instead of subtree
> thing?  This seems needlessly complicated. :(
>

I am for deprecating. If this is a long term goal, a two-phase process 
making it per-tree seems unnecessary and even more confusing.