Eric Dumazet wrote:
> 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 <[email protected]>
>>
>> ---
>> 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.
>
Hmm, how about:
struct futex_event {
union {
void __user *addr;
u64 padding;
};
union {
int val;
s64 val64;
};
/* whatever room is necessary for future improvements */
};
I haven't been keeping up with 64 bit or private futexes. What else
could probably go wrong?
--
Davi Arnaut
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