From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Kerrisk Subject: Re: [patch/rfc] eventfd semaphore-like behavior Date: Thu, 5 Feb 2009 13:26:32 +1300 Message-ID: References: <20090204150507.665b5b7c.akpm@linux-foundation.org> <20090204152434.c8f65d52.akpm@linux-foundation.org> <20090204155514.6abbdc8f.akpm@linux-foundation.org> <20090204161816.b93a4588.akpm@linux-foundation.org> Reply-To: mtk.manpages@gmail.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20090204161816.b93a4588.akpm@linux-foundation.org> Sender: linux-kernel-owner@vger.kernel.org To: Andrew Morton Cc: davidel@xmailserver.org, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, linux-api@vger.kernel.org List-Id: linux-api@vger.kernel.org On Thu, Feb 5, 2009 at 1:18 PM, Andrew Morton wrote: > On Thu, 5 Feb 2009 12:59:07 +1300 > Michael Kerrisk wrote: > >> >> > > > 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? >> >> >> > >> > 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. > > I think you means "should work" ;) > > We're talking about this, yes? > > SYSCALL_DEFINE2(eventfd2, unsigned int, count, int, flags) > { > int fd; > struct eventfd_ctx *ctx; > > /* Check the EFD_* constants for consistency. */ > BUILD_BUG_ON(EFD_CLOEXEC != O_CLOEXEC); > BUILD_BUG_ON(EFD_NONBLOCK != O_NONBLOCK); > > if (flags & ~(EFD_CLOEXEC | EFD_NONBLOCK)) > return -EINVAL; > > That looks like it should work to me. Yes, that's what we're talking about, plus a similar check that Ulrih added in the case that glibc's eventfd() falls back to sy_event(). Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ git://git.kernel.org/pub/scm/docs/man-pages/man-pages.git man-pages online: http://www.kernel.org/doc/man-pages/online_pages.html Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html