From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757248AbZBDX15 (ORCPT ); Wed, 4 Feb 2009 18:27:57 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752458AbZBDX1s (ORCPT ); Wed, 4 Feb 2009 18:27:48 -0500 Received: from x35.xmailserver.org ([64.71.152.41]:52855 "EHLO x35.xmailserver.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752127AbZBDX1r (ORCPT ); Wed, 4 Feb 2009 18:27:47 -0500 X-AuthUser: davidel@xmailserver.org Date: Wed, 4 Feb 2009 15:27:45 -0800 (PST) From: Davide Libenzi X-X-Sender: davide@alien.or.mcafeemobile.com To: Andrew Morton cc: Linux Kernel Mailing List , Linus Torvalds , Michael Kerrisk , linux-api@vger.kernel.org Subject: Re: [patch/rfc] eventfd semaphore-like behavior In-Reply-To: <20090204152434.c8f65d52.akpm@linux-foundation.org> Message-ID: References: <20090204150507.665b5b7c.akpm@linux-foundation.org> <20090204152434.c8f65d52.akpm@linux-foundation.org> User-Agent: Alpine 1.10 (DEB 962 2008-03-14) X-GPG-FINGRPRINT: CFAE 5BEE FD36 F65E E640 56FE 0974 BF23 270F 474E X-GPG-PUBLIC_KEY: http://www.xmailserver.org/davidel.asc MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 4 Feb 2009, Andrew Morton wrote: > On Wed, 4 Feb 2009 15:18:43 -0800 (PST) > Davide Libenzi wrote: > > > > > Simple test here: > > > > > > > > http://www.xmailserver.org/eventfd-sem.c > > > > > > > > > > > > Signed-off-by: Davide Libenzi > > > > > > > > +/* > > > > + * CAREFUL: Check include/asm-generic/fcntl.h when defining > > > > + * new flags, since they might collide with O_* ones. We want > > > > + * to re-use O_* flags that couldn't possibly have a meaning > > > > + * from eventfd, in order to leave a free define-space for > > > > + * shared O_* flags. > > > > + */ > > > > +#define EFD_SEMAPHORE (1 << 0) > > > > #define EFD_CLOEXEC O_CLOEXEC > > > > #define EFD_NONBLOCK O_NONBLOCK > > > > > > > > +#define EFD_SHARED_FCNTL_FLAGS (O_CLOEXEC | O_NONBLOCK) > > > > +#define EFD_FLAGS_SET (EFD_SHARED_FCNTL_FLAGS | EFD_SEMAPHORE) > > > > > > How would you recommend that userspace determine whether its kernel > > > supports this feature, bearing in mind that someone might backport this > > > patch into arbitrarily earlier kernel versions? > > > > > > What should be userspace's fallback strategy if that support is not > > > present? > > > > #ifdef EFD_SEMAPHORE, maybe? > > That's compile-time. People who ship binaries will probably want > to find a runtime thing for back-compatibility. I dunno. How do they actually do when we add new flags, like the O_ ones? - Davide