On Wed, 4 Feb 2009 16:25:52 -0800 (PST)
Davide Libenzi <davidel@xxxxxxxxxxxxxxx> wrote:
> On Wed, 4 Feb 2009, Andrew Morton wrote:
>
> > On Thu, 5 Feb 2009 12:59:07 +1300
> > Michael Kerrisk <mtk.manpages@xxxxxxxxxxxxxx> wrote:
> >
> > > >> > > > What should be userspace's fallback strategy if that support is not
> > > >> > > > present?
> > > >> > >
> > > >> > > #ifdef EFD_SEMAPHORE, maybe?
> > > >> >
> > > >> > That's compile-time. People who ship binaries will probably want
> > > >> > to find a runtime thing for back-compatibility.
> > > >>
> > > >> I dunno. How do they actually do when we add new flags, like the O_ ones?
> > > >>
> > > >
> > > > Dunno. Probably try the syscall and see if it returned -EINVAL. Does
> > > > that work in this case?
> > >
> > > As youll have seen by now, Ulrich and I noted that it works.
> >
> > I think you means "should work" ;)
> >
> > We're talking about this, yes?
> >
> > SYSCALL_DEFINE2(eventfd2, unsigned int, count, int, flags)
> > {
> > int fd;
> > struct eventfd_ctx *ctx;
> >
> > /* Check the EFD_* constants for consistency. */
> > BUILD_BUG_ON(EFD_CLOEXEC != O_CLOEXEC);
> > BUILD_BUG_ON(EFD_NONBLOCK != O_NONBLOCK);
> >
> > if (flags & ~(EFD_CLOEXEC | EFD_NONBLOCK))
> > return -EINVAL;
> >
> > That looks like it should work to me.
>
> I lost you guys. On old kernels you'd get -EINVAL when using the new flag.
> Wasn't it clear? Or is there some side-band traffic in this conversation
> that I missed? :)
>
Well yes, that. What I was trying to establish here is that we have
thought about (and preferably tested) userspace's back-compatibility
arrangements.
We have now done that.
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