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

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Date:   Sun, 7 Mar 2021 12:34:40 +0100
From:   Stefan Metzmacher <metze@...ba.org>
To:     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, Steven Rostedt <rostedt@...dmis.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     kernel@...labora.com, krisman@...labora.com,
        pgriffais@...vesoftware.com, z.figura12@...il.com,
        joel@...lfernandes.org, malteskarupke@...tmail.fm,
        linux-api@...r.kernel.org, fweimer@...hat.com,
        libc-alpha@...rceware.org, linux-kselftest@...r.kernel.org,
        shuah@...nel.org, acme@...nel.org, corbet@....net,
        io-uring <io-uring@...r.kernel.org>
Subject: Re: [RFC PATCH v2 00/13] Add futex2 syscall


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.  

With that in mind would it be good to have some interaction with epoll (and similar calls)?

Instead of having a blocked futex_waitv() waiting on an fd (maybe a generic eventfd() or a new futex2fd())
would be a better interface?

Or instead introduce an IORING_OP_FUTEX2_WAITV? Then the futex_waitv logic wait
in an io-wq kernel thread...

I guess the io_uring way would mean we could have that in mind as future addition, which can be implemented
later...

metze