Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1423926AbWKHXHc (ORCPT ); Wed, 8 Nov 2006 18:07:32 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1423927AbWKHXHc (ORCPT ); Wed, 8 Nov 2006 18:07:32 -0500 Received: from sp604005mt.neufgp.fr ([84.96.92.11]:65246 "EHLO smtp.Neuf.fr") by vger.kernel.org with ESMTP id S1423926AbWKHXHa (ORCPT ); Wed, 8 Nov 2006 18:07:30 -0500 Date: Thu, 09 Nov 2006 00:07:37 +0100 From: Eric Dumazet Subject: Re: [take23 0/5] kevent: Generic event handling mechanism. In-reply-to: To: Davide Libenzi Cc: Andrew Morton , Evgeniy Polyakov , David Miller , Ulrich Drepper , netdev , Zach Brown , Christoph Hellwig , Chase Venters , Johann Borck , Linux Kernel Mailing List , Jeff Garzik Message-id: <45526339.3040506@cosmosbay.com> MIME-version: 1.0 Content-type: text/plain; charset=ISO-8859-1; format=flowed Content-transfer-encoding: 8BIT References: <1154985aa0591036@2ka.mipt.ru> <20061107141718.f7414b31.akpm@osdl.org> <20061108082147.GA2447@2ka.mipt.ru> <200611081551.14671.dada1@cosmosbay.com> <20061108140307.da7d815f.akpm@osdl.org> User-Agent: Thunderbird 1.5.0.7 (Windows/20060909) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2519 Lines: 69 Davide Libenzi a ?crit : > On Wed, 8 Nov 2006, Andrew Morton wrote: > >> On Wed, 8 Nov 2006 15:51:13 +0100 >> Eric Dumazet 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 >>> >>> >>> >>> [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. > Sure poll() cannot return a partial count, since its return value is : On success, a positive number is returned, where the number returned is the number of structures which have non-zero revents fields (in other words, those descriptors with events or errors reported). poll() is non destructive (it doesnt change any state into kernel). Returning EFAULT in case of an error in the very last bit of user area is mandatory. On the contrary : epoll_wait() does return a count of transfered events, and update some state in kernel (it consume Edge Trigered events : They can be lost forever if not reported to user) So epoll_wait() is much more like read(), that also updates file state in kernel (current file position) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/