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Date:   Wed, 3 Mar 2021 17:12:20 -0800
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Eric Gao <eric.tech@foxmail.com>
Cc:     jbi.octave@gmail.com, linux-kernel@vger.kernel.org,
        Manfred Spraul <manfred@colorfullife.com>,
        Davidlohr Bueso <dave@stgolabs.net>
Subject: Re: [PATCH] ipc/msg: add msgsnd_timed and msgrcv_timed syscall for
 system V message queue
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On Tue, 23 Feb 2021 23:11:43 +0800 Eric Gao <eric.tech@foxmail.com> wrote:

> sometimes, we need the msgsnd or msgrcv syscall can return after a limited
> time, so that the business thread do not be blocked here all the time. In
> this case, I add the msgsnd_timed and msgrcv_timed syscall that with time
> parameter, which has a unit of ms.

Please cc Manfred and Davidlohr on ipc/ changes.

The above is a very brief description for a new syscall!  Please go to
great lengths to tell us why this is considered useful - what are the
use cases?

Also, please fully describe the proposed syscall interface right here
in the changelog.  Please be prepared to later prepare a full manpage.

> ...
> +SYSCALL_DEFINE5(msgsnd_timed, int, msqid, struct msgbuf __user *, msgp, size_t, msgsz,
> +		int, msgflg, long, timeoutms)

Specifying the timeout in milliseconds is problematic - it's very
coarse.  See sys_epoll_pwait2()'s use of timespecs.