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

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Message-ID: <CAJfpegvUCoKebYS=_3eZtCH49nObotuWc=_khFcHshKjRG8h6Q@mail.gmail.com>
Date:   Mon, 25 Sep 2023 15:13:36 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Christian Brauner <brauner@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Miklos Szeredi <mszeredi@...hat.com>,
        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>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Alexander 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, 25 Sept 2023 at 15:04, Christian Brauner <brauner@...nel.org> wrote:
>
> On Mon, Sep 25, 2023 at 02:57:31PM +0200, Arnd Bergmann wrote:
> > On Wed, Sep 13, 2023, at 17:22, Miklos Szeredi wrote:
> >
> > >  asmlinkage long sys_fstatfs64(unsigned int fd, size_t sz,
> > >                             struct statfs64 __user *buf);
> > > +asmlinkage long sys_statmnt(u64 mnt_id, u64 mask,
> > > +                       struct statmnt __user *buf, size_t bufsize,
> > > +                       unsigned int flags);
> >
> > This definition is problematic on 32-bit architectures for two
> > reasons:
> >
> > - 64-bit register arguments are passed in pairs of registers
> >   on two architectures, so anything passing those needs to
> >   have a separate entry point for compat syscalls on 64-bit
> >   architectures. I would suggest also using the same one on
> >   32-bit ones, so you don't rely on the compiler splitting
> >   up the long arguments into pairs.
> >
> > - There is a limit of six argument registers for system call
> >   entry points, but with two pairs and three single registers
> >   you end up with seven of them.
> >
> > The listmnt syscall in patch 3 also has the first problem,
> > but not the second.
>
> Both fields could also just be moved into the struct itself just like we
> did for clone3() and others.

Let's not mix in and out args, please.

How about passing u64 *?

Thanks,
Miklos