From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: [patch/rfc] eventfd semaphore-like behavior Date: Wed, 4 Feb 2009 15:24:34 -0800 Message-ID: <20090204152434.c8f65d52.akpm@linux-foundation.org> References: <20090204150507.665b5b7c.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Davide Libenzi Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org, mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-api@vger.kernel.org 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. -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html