linux-kernel - Re: [PATCH v4 00/15] Add futex2 syscalls

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Date:   Tue, 8 Jun 2021 15:27:32 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Andrey Semashev <andrey.semashev@...il.com>
Cc:     Nicholas Piggin <npiggin@...il.com>,
        André Almeida <andrealmeid@...labora.com>,
        acme@...nel.org, Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        corbet@....net, Davidlohr Bueso <dave@...olabs.net>,
        Darren Hart <dvhart@...radead.org>, fweimer@...hat.com,
        joel@...lfernandes.org, kernel@...labora.com,
        krisman@...labora.com, libc-alpha@...rceware.org,
        linux-api@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, malteskarupke@...tmail.fm,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        pgriffais@...vesoftware.com, Peter Oskolkov <posk@...k.io>,
        Steven Rostedt <rostedt@...dmis.org>, shuah@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>, z.figura12@...il.com
Subject: Re: [PATCH v4 00/15] Add futex2 syscalls

On Tue, Jun 08, 2021 at 04:18:42PM +0300, Andrey Semashev wrote:
> On 6/8/21 3:35 PM, Greg KH wrote:
> > On Tue, Jun 08, 2021 at 03:06:48PM +0300, Andrey Semashev wrote:
> > > On 6/8/21 2:13 PM, Greg KH wrote:
> > 
> > > > So what's keeping the futex2 code from doing all that futex1 does so
> > > > that the futex1 code can be deleted internally?
> > > 
> > > I think, André will answer this, but my guess is, as stated above, this is a
> > > lot of work and time while the intermediate version is already useful.
> > 
> > useful to who?  I still do not understand what users will be needing
> > this.  All I can tell is a single userspace program wants to use it, and
> > that is a fork from the real project it was based on and that the
> > maintainers have no plan to merge it back.
> > 
> > So who does need/want this?
> 
> I mentioned C++ std::atomic and Boost.Atomic before. Those need variable
> sized futexes.

And has anyone converted them to use this new api to see if it works
well or not?

As was pointed out to me numerous times when I tried to propose
readfile(), you need a real user that can show and prove it is needed
before we can take new syscalls, especially complex beasts like this
one.

thanks,

greg k-h