linux-kernel - Re: Question about select and poll system call

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Message-ID: <CAJNi4rO6TiZFFKTcW3kGgha2Rc0nTsXRLyeqAyYrN3foLbExSQ@mail.gmail.com>
Date:   Tue, 14 Mar 2023 10:31:42 +0800
From:   richard clark <richard.xnu.clark@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     torvalds@...ux-foundation.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: Question about select and poll system call

Adding linux-arm-kernel@...ts.infradead.org ... for more possible feedback:)

On Tue, Mar 14, 2023 at 10:28 AM richard clark
<richard.xnu.clark@...il.com> wrote:
>
> Hi, (Sorry, not find the maintainers for this subsystem, so to the lkml)
>
> There're two questions about these system calls:
> 1. According to https://pubs.opengroup.org/onlinepubs/7908799/xsh/select.html:
> ERRORS
> [EINVAL]
>       The nfds argument is less than 0 or greater than FD_SETSIZE.
> But the current implementation in Linux like:
>        if (nfds > FD_SETSIZE)
>                nfds = FD_SETSIZE
> What's the rationale behind this?
>
> 2. Can we unify the two different system calls? For example, using
> poll(...) to implement the frontend select call(...), is there
> something I'm missing for current implementation? The Cons and Pros,
> etc
>
> Thanks,