Re: [PATCH v2 1/1] eventfd: implementation of EFD_MASK flag

On Fri, 15 Feb 2013 04:42:27 +0100 Martin Sustrik [off-list ref] wrote:

quoted

This is a non-back-compatible userspace interface change.  A procfs
file which previously displayed

	eventfd-count: nnnn

can now also display

	eventfd-mask: nnnn

So existing userspace could misbehave.

Please fully describe the proposed interface change in the changelog.
That description should include the full pathname of the procfs file
and example before-and-after output and a discussion of whether and why
the risk to existing userspace is acceptable.

I am not sure what the policy is here. Is not printing out the state of 
the object acceptable way to maintain backward compatibility? If not so, 
does new type of object require new procfs file, which, AFAIU, is the 
only way to retain full backward compatibility?

Adding a new file is the only way I can think of to preserve the API. 
But from Andy's comment is sounds like we don't have to worry a lot
about back-compatibility.