Re: [PATCH] fix bad behavior in use_hierarchy file

[Tejun Heo <tj@kernel.org>]

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. :(

-- 
tejun

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