Re: [PATCH] ipc/msg: add msgsnd_timed and msgrcv_timed syscall for system V message queue

[Andrew Morton <akpm@linux-foundation.org>]

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.