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

Andrew Morton
2006-11-08T22:08:35Z

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...