Eric Dumazet wrote:
> Davi Arnaut a écrit :
>> 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?
>
> Well, that's the point : This interface is like an ioctl() one : pretty bad
> if
> not properly designed :)
>
> You probably need to stick one field containing one command or version
> number,
> something like that.
>
>
> struct futex_event {
> int type;
> union {
> void __user *addr;
> u64 padding;
> };
> union {
> int val;
> s64 val64;
> };
> };
>
> #define FUTEX_EVENT_SHARED32 1
> #define FUTEX_EVENT_SHARED64 2
> #define FUTEX_EVENT_PRIVATE32 (128|1)
> #define FUTEX_EVENT_PRIVATE64 (128|2)
>
I'm changing the structure to:
struct futex_event {
union {
void __user *addr;
u64 addr64;
};
union {
int val;
s64 val64;
};
union {
s32 flags;
s64 flags64;
};
};
Plenty room for future FUTEX_WAIT growth ?
--
Davi Arnaut
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