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From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: linux-api <linux-api@vger.kernel.org>,
	Peter Oskolkov <posk@google.com>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: Is adding an argument to an existing syscall okay?
Date: Tue, 17 Nov 2020 09:28:41 -0500 (EST)	[thread overview]
Message-ID: <621527792.47384.1605623321460.JavaMail.zimbra@efficios.com> (raw)
In-Reply-To: <CALCETrXU2KcH0nsH_vd-fmvpZt_yW2+=VnYtN_BQJ6xsSvm+6A@mail.gmail.com>

----- On Nov 16, 2020, at 6:57 PM, Andy Lutomirski luto@kernel.org wrote:

> Linux 5.10 contains this patch:
> 
> commit 2a36ab717e8fe678d98f81c14a0b124712719840
> Author: Peter Oskolkov <posk@google.com>
> Date:   Wed Sep 23 16:36:16 2020 -0700
> 
>    rseq/membarrier: Add MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ
> 
> This adds an argument to an existing syscall.  Before the patch,
> membarrier had 2 parameters; now it has 3.  Is this really okay?  At
> least the patch is careful and ignores the third parameter unless a
> previously unused flag bit is set.

Hi Andy,

I wondered about exactly this on August 12 2020:

https://lore.kernel.org/r/1477195446.6156.1597261492255.JavaMail.zimbra@efficios.com

And then on August 25, after receiving no feedback, I told Peter to try this approach:

https://lore.kernel.org/r/1336467655.17779.1598374701401.JavaMail.zimbra@efficios.com

and nobody complained until now. As you note, the extra argument is only used when
previously unused flag bits are set.

So your question is very relevant, and I still look forward to receiving feedback
on this matter.

Thanks,

Mathieu

> 
> --Andy

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

  reply	other threads:[~2020-11-17 14:29 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-16 23:57 Is adding an argument to an existing syscall okay? Andy Lutomirski
2020-11-17 14:28 ` Mathieu Desnoyers [this message]
2020-11-17 17:05 ` Theodore Y. Ts'o
2020-11-17 17:16 ` Florian Weimer
2020-11-17 18:36   ` Segher Boessenkool
2020-11-17 18:44     ` Florian Weimer
2020-11-17 18:58       ` Peter Oskolkov
2020-11-17 19:21         ` Mathieu Desnoyers
2020-11-17 19:32           ` Peter Oskolkov
2020-11-17 19:45           ` Florian Weimer
2020-11-19  3:08 ` Aleksa Sarai

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