Messages in this thread | | | Date | Wed, 02 May 2007 07:54:34 +0200 | From | Eric Dumazet <> | Subject | Re: [patch 14/22] pollfs: pollable futex |
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Davi Arnaut a écrit : > Asynchronously wait for FUTEX_WAKE operation on a futex if it still contains > a given value. There can be only one futex wait per file descriptor. However, > it can be rearmed (possibly at a different address) anytime. > > The pollable futex approach is far superior (send and receive events from > userspace or kernel) to eventfd and fixes (supercedes) FUTEX_FD at the same time. > > Building block for pollable semaphores and user-defined events. > > Signed-off-by: Davi E. M. Arnaut <davi@haxent.com.br> > > --- > fs/pollfs/Makefile | 1 > fs/pollfs/futex.c | 154 +++++++++++++++++++++++++++++++++++++++++++++++++++++ > init/Kconfig | 7 ++ > 3 files changed, 162 insertions(+) > > Index: linux-2.6/fs/pollfs/Makefile > =================================================================== > --- linux-2.6.orig/fs/pollfs/Makefile > +++ linux-2.6/fs/pollfs/Makefile > @@ -3,3 +3,4 @@ pollfs-y := file.o > > pollfs-$(CONFIG_POLLFS_SIGNAL) += signal.o > pollfs-$(CONFIG_POLLFS_TIMER) += timer.o > +pollfs-$(CONFIG_POLLFS_FUTEX) += futex.o > Index: linux-2.6/fs/pollfs/futex.c > =================================================================== > --- /dev/null > +++ linux-2.6/fs/pollfs/futex.c > @@ -0,0 +1,154 @@ > +/* > + * pollable futex > + * > + * Copyright (C) 2007 Davi E. M. Arnaut > + * > + * Licensed under the GNU GPL. See the file COPYING for details. > + */ > + > +#include <linux/kernel.h> > +#include <linux/sched.h> > +#include <linux/module.h> > +#include <linux/slab.h> > +#include <linux/err.h> > +#include <linux/wait.h> > +#include <linux/poll.h> > +#include <linux/pollfs_fs.h> > +#include <linux/futex.h> > + > +struct futex_event { > + union { > + void __user *addr; > + u64 padding; > + }; > + int val; > +};
Hum... Here we might have a problem with 64 bit futexes, or private futexes
So I believe this interface is not well defined and not expandable: in case of future additions to futexes, an old application compiled with an old pollable futex_event type might fail.
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