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

From: Martin Sustrik
Date: Fri Feb 15 2013 - 13:37:16 EST

On 15/02/13 18:32, Andy Lutomirski wrote:
On Thu, Feb 14, 2013 at 9:24 PM, Andrew Morton
<akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
On Fri, 15 Feb 2013 04:42:27 +0100 Martin Sustrik<sustrik@xxxxxxxxxx> wrote:

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.

I'm not even convinced there's an issue in the first place (other than
the fact that use of this feature will break old criu, regardless of
/proc changes). The fdinfo files already vary by descriptor type.
Anything that screws up if unexpected fields are present is already

Ok then. I'll leave the relevant code as is.

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