Re: [take23 0/5] kevent: Generic event handling mechanism.

Davide Libenzi
2006-11-08T22:44:57Z

On Wed, 8 Nov 2006, Andrew Morton wrote:

> On Wed, 8 Nov 2006 15:51:13 +0100
> Eric Dumazet <dada1@cosmosbay.com> wrote:
>
> > [PATCH] eventpoll : In case a fault occurs during copy_to_user(), we should
> > report the count of events that were successfully copied into user space,
> > instead of EFAULT. That would be consistent with behavior of read/write()
> > syscalls for example.
> >
> > Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
> >
> >
> >
> > [eventpoll.patch text/plain (424B)]
> > --- linux/fs/eventpoll.c 2006-11-08 15:37:36.000000000 +0100
> > +++ linux/fs/eventpoll.c 2006-11-08 15:38:31.000000000 +0100
> > @@ -1447,7 +1447,7 @@
> > &events[eventcnt].events) ||
> > __put_user(epi->event.data,
> > &events[eventcnt].data))
> > - return -EFAULT;
> > + return eventcnt ? eventcnt : -EFAULT;
> > if (epi->event.events & EPOLLONESHOT)
> > epi->event.events &= EP_PRIVATE_BITS;
> > eventcnt++;
> >
>
> Definitely a better interface, but I wonder if it's too late to change it.
>
> An app which does
>
> if (epoll_wait(...) == -1)
> barf(errno);
> else
> assume_all_events_were_received();
>
> will now do the wrong thing.
>
> otoh, such an applciation basically _has_ to use the epoll_wait()
> return value to work out how many events it received, so maybe it's OK...

I don't care about both ways, but sys_poll() does the same thing epoll
does right now, so I would not change epoll behaviour.

- Davide