MIME-Version: 1.0
From:   richard clark <richard.xnu.clark@gmail.com>
Date:   Tue, 14 Mar 2023 10:28:23 +0800
Message-ID: <CAJNi4rNSHf3N6KrBNcVXKo-wjSPmZa2xan9WPmrER8Ttir-MDA@mail.gmail.com>
Subject: Question about select and poll system call
To:     linux-kernel@vger.kernel.org
Cc:     torvalds@linux-foundation.org
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

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,