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

[Martin Sustrik]

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
> screwed.

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

Martin
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