On Wed, 4 Feb 2009 15:27:45 -0800 (PST) Davide Libenzi <davidel@xxxxxxxxxxxxxxx> wrote: > On Wed, 4 Feb 2009, Andrew Morton wrote: > > > On Wed, 4 Feb 2009 15:18:43 -0800 (PST) > > Davide Libenzi <davidel@xxxxxxxxxxxxxxx> wrote: > > > > > > > Simple test here: > > > > > > > > > > http://www.xmailserver.org/eventfd-sem.c > > > > > > > > > > > > > > > Signed-off-by: Davide Libenzi <davidel@xxxxxxxxxxxxxxx> > > > > > > > > > > +/* > > > > > + * 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? > Dunno. Probably try the syscall and see if it returned -EINVAL. Does that work in this case? If so, it would be sensible to mention this in the description somewhere as the approved probing method and to maintain it. -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
