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

[Nathan Lynch <ntl@pobox.com>]

On Tue, 2010-07-20 at 21:10 -0700, Andrew Morton wrote:
> 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.

Yes, I misinterpreted your concern, sorry.  But I've never understood
Linux to make promises with respect to forward compatibility at the
system call layer.  Bug fixes[1] and features[2] that, like this patch,
break that compatibility seem to have gone in without raising this
issue.

Am I mistaken?  Or has there been a change in policy I've missed?


[1] "signalfd: fix for incorrect SI_QUEUE user data reporting" (0859ab5)

[2] "hugetlb: add MAP_HUGETLB for mmaping pseudo-anonymous huge page
regions" (4e52780)