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

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Date:   Wed, 1 Jun 2022 20:25:20 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.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 01, 2022 at 12:23:06PM -0700, Linus Torvalds wrote:
> On Wed, Jun 1, 2022 at 12:19 PM Matthew Wilcox <willy@...radead.org> wrote:
> >
> > Why not pass the iocb in ->read and ->write?  We're still regretting not
> > doing that with file_operations.
> 
> No, all the actual "io" is done by the caller.
> 
> There is no way in hell I want the sysctl callbacks to actually
> possibly do user space accesses etc.
> 
> They get a kernel buffer that has already been set up. There is no
> iocb or iovec left for them.

I wasn't suggesting the iovec.  Just the iocb, instead of passing in the
ki_filp and the ki_pos.

> (That also means that they can take whatever locks they need,
> including spinlocks, because there's not going to be any random user
> accesses or complex pipe buffer lookups or whatever).
> 
>                 Linus