linux-kernel - Re: [RFC PATCH 2/3] add statmnt(2) syscall

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Message-ID: <20230918-hierbei-erhielten-ba5ef74a5b52@brauner>
Date:   Mon, 18 Sep 2023 16:24:55 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     Miklos Szeredi <mszeredi@...hat.com>
Cc:     Miklos Szeredi <miklos@...redi.hu>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org, linux-man@...r.kernel.org,
        linux-security-module@...r.kernel.org, Karel Zak <kzak@...hat.com>,
        Ian Kent <raven@...maw.net>,
        David Howells <dhowells@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <christian@...uner.io>,
        Amir Goldstein <amir73il@...il.com>
Subject: Re: [RFC PATCH 2/3] add statmnt(2) syscall

On Mon, Sep 18, 2023 at 04:14:02PM +0200, Miklos Szeredi wrote:
> On Mon, Sep 18, 2023 at 3:51 PM Christian Brauner <brauner@...nel.org> wrote:
> 
> > I really would prefer a properly typed struct and that's what everyone
> > was happy with in the session as well. So I would not like to change the
> > main parameters.
> 
> I completely  agree.  Just would like to understand this point:
> 
>   struct statmnt *statmnt(u64 mntid, u64 mask, unsigned int flags);
> 
> What's not properly typed about this interface?
> 
> I guess the answer is that it's not a syscall interface, which will
> have an added [void *buf, size_t bufsize], while the buffer sizing is
> done by a simple libc wrapper.
> 
> Do you think that's a problem?  If so, why?

Sorry, I think we just talked passed each other.
I didn't realize you were talking about a glibc wrapper.
I'm not so much concerned with that they can expose this in whathever
way they like. But we will have a lot of low-level userspace that will
directly use statmount() or not even have glibc like go and other
languages.

The system call should please have a proper struct like you had in your
first proposal. This is what I'm concerned about:

int statmount(u64 mnt_id,
              struct statmnt __user *st,
              size_t size,
              unsigned int flags)

instead of taking an void pointer.