linux-kernel - Re: [RFC PATCH 1/4] sysctl: API extension for handling sysctl

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Date:   Wed, 1 Jun 2022 12:31:58 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Alexey Gladkov <legion@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christian Brauner <brauner@...nel.org>,
        Iurii Zaikin <yzaikin@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Linux Containers <containers@...ts.linux.dev>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Vasily Averin <vvs@...tuozzo.com>
Subject: Re: [RFC PATCH 1/4] sysctl: API extension for handling sysctl

On Wed, Jun 1, 2022 at 12:25 PM Matthew Wilcox <willy@...radead.org> wrote:
>
> I wasn't suggesting the iovec.  Just the iocb, instead of passing in the
> ki_filp and the ki_pos.

I guess that would work, but would it actually help anything?

I think it's a lot more obvious when it just looks mostly like a
"read/write()" system call (ok, pread/pwrite since you get the pos,
but still).

There is nothing that could possibly be relevant in the kiocb. All
those fields are about odd async or atomicity issues (or "report
completion" issues) that simply cannot possibly be valid for a sysctl
value.

And if they are, that sysctl value is doing something really really
really wrong. So we absolutely don't want to encourage that.

This is not a "do IO" interface. This is a "read or write value" interface.

               Linus