linux-kernel - Re: [RFC PATCH v2 00/13] Add futex2 syscall

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Date:   Mon, 8 Mar 2021 12:55:47 +0100
From:   Stefan Metzmacher <metze@...ba.org>
To:     David Laight <David.Laight@...LAB.COM>,
        André Almeida <andrealmeid@...labora.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Darren Hart <dvhart@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     "kernel@...labora.com" <kernel@...labora.com>,
        "krisman@...labora.com" <krisman@...labora.com>,
        "pgriffais@...vesoftware.com" <pgriffais@...vesoftware.com>,
        "z.figura12@...il.com" <z.figura12@...il.com>,
        "joel@...lfernandes.org" <joel@...lfernandes.org>,
        "malteskarupke@...tmail.fm" <malteskarupke@...tmail.fm>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "fweimer@...hat.com" <fweimer@...hat.com>,
        "libc-alpha@...rceware.org" <libc-alpha@...rceware.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "shuah@...nel.org" <shuah@...nel.org>,
        "acme@...nel.org" <acme@...nel.org>,
        "corbet@....net" <corbet@....net>,
        io-uring <io-uring@...r.kernel.org>
Subject: Re: [RFC PATCH v2 00/13] Add futex2 syscall

Am 08.03.21 um 12:11 schrieb David Laight:
> From: Stefan Metzmacher
>> Sent: 07 March 2021 11:35
>>
>> Hi André,
>>>  ** The wait on multiple problem
>>>
>>>  The use case lies in the Wine implementation of the Windows NT interface
>>>  WaitMultipleObjects. This Windows API function allows a thread to sleep
>>>  waiting on the first of a set of event sources (mutexes, timers, signal,
>>>  console input, etc) to signal.
> 
> They are all events.
> You can only wait on either events or sockets (using select).
> There is a socket api to signal an event when data arrives (etc).
> There is also the insane (these days) restriction of 64 events.

Ok.

>> With that in mind would it be good to have some interaction with epoll (and similar calls)?
> 
> Or hook something up so that pollwakeup can kick a futex as well
> as waking up poll() and adding an event to epoll().

I guess as FUTEX_FD was already there and was removed we can stop this discussion.

If there will every be the need to an async call, I guess a io_uring based one would
be the best...

metze