Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932391AbXIEQYI (ORCPT ); Wed, 5 Sep 2007 12:24:08 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755845AbXIEQXz (ORCPT ); Wed, 5 Sep 2007 12:23:55 -0400 Received: from mail.gmx.net ([213.165.64.20]:54398 "HELO mail.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1756758AbXIEQXy (ORCPT ); Wed, 5 Sep 2007 12:23:54 -0400 Cc: akpm@linux-foundation.org, corbet@lwn.net, jengelh@computergmbh.de, hch@lst.de, stable@kernel.org, drepper@redhat.com, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, rdunlap@xenotime.net Content-Type: text/plain; charset="us-ascii" Date: Wed, 05 Sep 2007 18:23:52 +0200 From: "Michael Kerrisk" In-Reply-To: Message-ID: <20070905162352.236680@gmx.net> MIME-Version: 1.0 References: <20070825064114.107820@gmx.net> <46DD116C.4040301@gmx.net> <20070904011800.762523a4.akpm@linux-foundation.org> <20070904204932.208520@gmx.net> <20070905000831.313400@gmx.net> Subject: Re: [PATCH] Revised timerfd() interface To: Davide Libenzi X-Authenticated: #24879014 X-Flags: 0001 X-Mailer: WWW-Mail 6100 (Global Message Exchange) X-Priority: 3 X-Provags-ID: V01U2FsdGVkX1/8xJlU15D87F/TzH5TsVK1f7b39gz+J+GuvKu2M0 5aely2tIqlbvpEk5PNGhmZiYep2Pf8IYSKKw== Content-Transfer-Encoding: 7bit X-GMX-UID: LOrsdUVrPTR+cpGsSjMww505c2tpZIt6 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2040 Lines: 50 Hi Davide, > > > > As I think about this more, I see more problems with > > > > your argument. timerfd needs the ability to get and > > > > get-while-setting just as much as the earlier APIs. > > > > Consider a library that creates a timerfd file descriptor that > > > > is handed off to an application: that library may want > > > > to modify the timer settings without having to create a > > > > new file descriptor (the app mey not be able to be told about > > > > the new fd). Your argument just doesn't hold, AFAICS. > > > > > > Such hypotethical library, in case it really wanted to offer such > > > functionality, could simply return an handle instead of the raw fd, > > > and take care of all that stuff in userspace. > > > > Did I miss something? Is it not the case that as soon as the > > library returns a handle, rather than an fd, then the whole > > advantage of timerfd() (being able to select/poll/epoll on > > the timer as well as other fds) is lost? > > Why? The handle would simply be a little struct where the timerfd fd is > stored, and a XXX_getfd() would return it. > So my point is, I doubt such functionalities are really needed, and I > also argue that the kernel is the best place for such wrapper code > to go. So what happens if one thread (via the library) wants modify a timer's settings at the same timer as another thread is select()ing on it? The first thread can't do this by creating a new timerfd timer, since it wants to affect the select() in the other thread? Cheers, Michael -- Michael Kerrisk maintainer of Linux man pages Sections 2, 3, 4, 5, and 7 Want to help with man page maintenance? Grab the latest tarball at http://www.kernel.org/pub/linux/docs/manpages , read the HOWTOHELP file and grep the source files for 'FIXME'. - 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/