linux-kernel - Re: [RFC PATCH 1/2] rust: list: Implement normal initializer for ListLinks

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Message-ID: <CAH5fLgiUj7R4SvKYT3HGxqSDnjs4T6EKB91bX1JFe-a9a=fHsg@mail.gmail.com>
Date: Mon, 10 Mar 2025 12:44:12 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: I Hsin Cheng <richard120310@...il.com>
Cc: ojeda@...nel.org, alex.gaynor@...il.com, boqun.feng@...il.com, 
	gary@...yguo.net, bjorn3_gh@...tonmail.com, benno.lossin@...ton.me, 
	a.hindborg@...nel.org, tmgross@...ch.edu, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org, skhan@...uxfoundation.org, 
	linux-kernel-mentees@...ts.linux.dev, jserv@...s.ncku.edu.tw
Subject: Re: [RFC PATCH 1/2] rust: list: Implement normal initializer for ListLinks

On Mon, Mar 10, 2025 at 12:14 PM I Hsin Cheng <richard120310@...il.com> wrote:
>
> On Mon, Mar 10, 2025 at 09:44:41AM +0000, Alice Ryhl wrote:
> > On Mon, Mar 10, 2025 at 03:30:39PM +0800, I Hsin Cheng wrote:
> > > Currently ListLinks only supports to create an initializer through
> > > "new()", which will need further initialization because the return type
> > > of "new()" is "impl Pininit<Self>". Not even "ListLinksSlefPtr" use the
> > > method to create a new instance of "ListLinks".
> > >
> > > Implement a normal method to create a new instance of type "ListLinks".
> > > This may be redundant as long as there exist a convenient and proper way
> > > to deal with "ListLinks::new()".
> > >
> > > For now it's introduce for the simplicity of examples in the following
> > > patches.
> > >
> > > Signed-off-by: I Hsin Cheng <richard120310@...il.com>
> >
> > This change is not good. The ListLinks type has an invariant about when
> > the pointers are null. The existing constructor argues that the
> > invariant is satisfied because pin-init initializers can't be used in an
> > existing Arc. Why is that satisfied here?
> >
> > Alice
>
> Hi Alice,
>
> Thanks for your kindly review. Indeed , I was trying to find a way to
> cope with "ListLinks::new()", wondering if there's any macros like
> "ListLinks::try_pin_init!()" to help us deal with "impl PinInit", so I
> try to send a RFC patch for it.
>
> Sorry I overlooked "commit 52ae96f"[1], it demonstrate a good way to
> handle the basic structure for "List", I'll fix the patch and send a v2
> as soon as possible.
>
> Still I would love to ask why don't we provide "ListLinks::pin_init" or
> "ListLinks::try_pin_init" to support for the pin-init initializer
> returned by "ListLink::new()" ? Maybe there're special reasons behind
> the pin-init initializer here ? I would love to learn if that's
> possible.
>
> I tried "Kbox::pint_init" but it
> wouldn't give variable of type "ListLinks".

Please see the examples from:
https://lore.kernel.org/rust-for-linux/20250210-cursor-between-v7-2-36f0215181ed@google.com/

Alice