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

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Message-Id: <20061108140307.da7d815f.akpm@osdl.org>
Date:	Wed, 8 Nov 2006 14:03:07 -0800
From:	Andrew Morton <akpm@...l.org>
To:	Eric Dumazet <dada1@...mosbay.com>
Cc:	Evgeniy Polyakov <johnpol@....mipt.ru>,
	David Miller <davem@...emloft.net>,
	Ulrich Drepper <drepper@...hat.com>,
	netdev <netdev@...r.kernel.org>,
	Zach Brown <zach.brown@...cle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Chase Venters <chase.venters@...entec.com>,
	Johann Borck <johann.borck@...sedata.com>,
	linux-kernel@...r.kernel.org, Jeff Garzik <jeff@...zik.org>,
	Davide Libenzi <davidel@...ilserver.org>
Subject: Re: [take23 0/5] kevent: Generic event handling mechanism.

On Wed, 8 Nov 2006 15:51:13 +0100
Eric Dumazet <dada1@...mosbay.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@...mosbay.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...
-
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