Re: [PATCH] signalfd: fill in ssi_int for posix timers and message queues

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 20 Jul 2010 22:44:19 -0500 Nathan Lynch <ntl@pobox.com> wrote:

> > So it's not 100% obvious that this change is desirable.  Does the
> > functionality which this patch adds justify the introduction of these
> > problems?
> 
> I think the change is desirable in that no user of the interface could
> reasonably expect the current behavior with respect to the ssi_int
> field, and that it reconciles signalfd's behavior with its design
> intentions.  On the other hand, I noticed this discrepancy only because
> I was cribbing signalfd's data structures for checkpoint/restart, not
> because I am aware of any application that is affected, nor was I able
> to find one using Google's code search.  It would be highly speculative
> of me to say that no application depends on the current behavior, but it
> is difficult to imagine a correctly functioning application that depends
> on it.

It's not a matter of a current application depending on current
behaviour!  The problem is that an application written in 2018 which
depends on the _new_ behaviour will not work on 2.6.34.

It wouldn't be the worst thing we've ever done to our long-suffering
users, but it is a permanent cost of having screwed things up :(