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Date:   Tue, 19 Sep 2023 15:18:03 +0200
From:   Christian Brauner <brauner@kernel.org>
To:     Miklos Szeredi <miklos@szeredi.hu>
Cc:     Matthew House <mattlloydhouse@gmail.com>,
        Miklos Szeredi <mszeredi@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-api@vger.kernel.org, linux-man@vger.kernel.org,
        linux-security-module@vger.kernel.org, Karel Zak <kzak@redhat.com>,
        Ian Kent <raven@themaw.net>,
        David Howells <dhowells@redhat.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <christian@brauner.io>,
        Amir Goldstein <amir73il@gmail.com>
Subject: Re: [RFC PATCH 2/3] add statmnt(2) syscall
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On Tue, Sep 19, 2023 at 02:59:53PM +0200, Miklos Szeredi wrote:
> On Tue, 19 Sept 2023 at 14:41, Christian Brauner <brauner@kernel.org> wrote:
> >
> > > >  with __u32 size for mnt_root and mnt_point
> > >
> > > Unnecessary if the strings are nul terminated.
> >
> > All ok by me so far but how does the kernel know the size of the buffer
> > to copy into? Wouldn't it be better to allow userspace to specify that?
> > I'm probably just missing something but I better ask.
> 
> Because size of the buffer is given as the syscall argument.
> 
>   long statmount(u64 mnt_id, u64 mask, struct statmnt __user *buf,
> size_t bufsize, unsigned int flags);
> 
> If you are still hung up about this not being properly typed, how about this:

I really just wasn't clear how exactly you envisioned this. Your
proposal as is sounds good to me! I'm on board. I prefer the two offsets
as that lets us avoid searching for null bytes. So please leave it as is!
Thanks!