linux-kernel - Re: [PATCH v2 2/7] rust: cred: add Rust abstraction for `struct cred`

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Date:   Mon, 11 Dec 2023 09:35:40 -0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     Alice Ryhl <aliceryhl@...gle.com>
Cc:     a.hindborg@...sung.com, alex.gaynor@...il.com, arve@...roid.com,
        benno.lossin@...ton.me, bjorn3_gh@...tonmail.com,
        brauner@...nel.org, cmllamas@...gle.com, dan.j.williams@...el.com,
        dxu@...uu.xyz, gary@...yguo.net, gregkh@...uxfoundation.org,
        joel@...lfernandes.org, keescook@...omium.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        maco@...roid.com, ojeda@...nel.org, peterz@...radead.org,
        rust-for-linux@...r.kernel.org, surenb@...gle.com,
        tglx@...utronix.de, tkjos@...roid.com, viro@...iv.linux.org.uk,
        wedsonaf@...il.com, willy@...radead.org
Subject: Re: [PATCH v2 2/7] rust: cred: add Rust abstraction for `struct cred`

On Mon, Dec 11, 2023 at 03:34:29PM +0000, Alice Ryhl wrote:
> Boqun Feng <boqun.feng@...il.com> writes:
> > On Wed, Dec 06, 2023 at 11:59:47AM +0000, Alice Ryhl wrote:
> > [...]
> > > @@ -151,6 +152,21 @@ pub fn as_ptr(&self) -> *mut bindings::file {
> > >          self.0.get()
> > >      }
> > >  
> > > +    /// Returns the credentials of the task that originally opened the file.
> > > +    pub fn cred(&self) -> &Credential {
> > 
> > I wonder whether it would be helpful if we use explicit lifetime here:
> > 
> >     pub fn cred<'file>(&'file self) -> &'file Credential
> > 
> > It might be easier for people to get. For example, the lifetime of the
> > returned Credential reference is constrainted by 'file, the lifetime of
> > the file reference.
> > 
> > But yes, maybe need to hear others' feedback first.
> > 
> > Regards,
> > Boqun
> 
> That would trigger a compiler warning because the lifetime is
> unnecessary.
> 

We can disable that warning if people need the information. Code is
mostly for reading, less often for compilation and changes.

> The safety comment explains what the signature means. I think that
> should be enough.
> 

For someone who has a good understanding of Rust lifetime (and the
elision), yes. But I'm wondering whether all the people feel the same
way.

Regards,
Boqun

> Alice