Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754228Ab0H3FV2 (ORCPT ); Mon, 30 Aug 2010 01:21:28 -0400 Received: from mail-vw0-f46.google.com ([209.85.212.46]:59265 "EHLO mail-vw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753664Ab0H3FV0 convert rfc822-to-8bit (ORCPT ); Mon, 30 Aug 2010 01:21:26 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:reply-to:in-reply-to:references:from:date:message-id :subject:to:cc:content-type:content-transfer-encoding; b=JR2PH72eY8M7lnKAogXpweRjc8kmvv7KB0FqeoTOnVHKWA4txM5AMz0WpFUPTKT1YN HO1J6KzBcJYwsRFfHDv/ktdhgbPqs4QFc1Ks3icLK0YS1PONkvXhi9t3Ipy81qph+Ym4 7zwQtwrVhG/SH/DrL8iWJAsQOWavxKZ++xvyY= MIME-Version: 1.0 Reply-To: mtk.manpages@gmail.com In-Reply-To: References: <20090204150507.665b5b7c.akpm@linux-foundation.org> <20090204152434.c8f65d52.akpm@linux-foundation.org> <20090204155514.6abbdc8f.akpm@linux-foundation.org> From: Michael Kerrisk Date: Mon, 30 Aug 2010 07:21:05 +0200 Message-ID: Subject: Re: [patch/rfc] eventfd semaphore-like behavior To: Davide Libenzi Cc: Andrew Morton , Linux Kernel Mailing List , Linus Torvalds , linux-api@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1937 Lines: 52 On Thu, Feb 5, 2009 at 2:02 AM, Davide Libenzi wrote: > On Thu, 5 Feb 2009, Michael Kerrisk wrote: > >> > Dunno. ?Probably try the syscall and see if it returned -EINVAL. ?Does >> > that work in this case? >> >> As youll have seen by now, Ulrich and I noted that it works. >> >> > If so, it would be sensible to mention this in >> > the description somewhere as the approved probing method and to >> > maintain it. >> >> I'll add something to the man page, as this patch progresses. > > I see we already have stuff like this inside the man pages: > > O_CLOEXEC (Since Linux 2.6.23) > ? ? ? ? ?Enable the close-on-exec flag for the new file descriptor. > ? ? ? ? ?... > > Maybe a similar note for the new flag? It took a while, but here's the new text in the eventfd.2 (will be in man-pages-2.36). Could you please ACK, Davide? EFD_SEMAPHORE (since Linux 2.6.30) Provide semaphore-like semantics for reads from the new file descriptor. See below. ... * If EFD_SEMAPHORE was not specified and the eventfd counter has a nonzero value, then a read(2) returns 8 bytes containing that value, and the counter's value is reset to zero. * If EFD_SEMAPHORE was specified and the eventfd counter has a nonzero value, then a read(2) returns 8 bytes containing the value 1, and the counter's value is decremented by 1. Thanks, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Author of "The Linux Programming Interface"; http://man7.org/tlpi/ -- 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/