linux-kernel - Re: [PATCH 2/3] rust: macros: allow generic parameter default values in `#[pin

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Message-ID: <2023112514-laziness-valium-7a25@gregkh>
Date:   Sat, 25 Nov 2023 15:10:36 +0000
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Benno Lossin <benno.lossin@...ton.me>
Cc:     Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Andreas Hindborg <a.hindborg@...sung.com>,
        Alice Ryhl <aliceryhl@...gle.com>,
        Martin Rodriguez Reboredo <yakoyoku@...il.com>,
        rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] rust: macros: allow generic parameter default values
 in `#[pin_data]`

On Sat, Nov 25, 2023 at 03:02:00PM +0000, Benno Lossin wrote:
> On 25.11.23 15:26, Greg KH wrote:
> > On Sat, Nov 25, 2023 at 12:51:09PM +0000, Benno Lossin wrote:
> >> This patch adds compatibilty for generic parameters defaults by using
> >> the newly introduced `decl_generics` instead of the `impl_generics`.
> > 
> > This says _what_ is happening here, but not _why_ this is needed at all.
> > 
> > Try taking a look a the kernel documentation for how to write a good
> > changelog text to make this much better.  It's often times the most
> > difficult portion of making a kernel patch, the code is easy, writing a
> > summary of why everyone else should agree that this code is acceptable
> > is hard.
> 
> The reason is hidden in the third patch.

Please do not hide things, patches need to be stand-alone and
understandable that way, otherwise they will be rejected as no one can
understand why they would be needed.

> Without this, the `#[pin_data]
> macro would not allow specifying const generic parameter default values
> and instead emit a compile error.

That's nice, but it still doesn't tell me _why_ this is needed.  Why
would I want any generic paramter default values at all?  Who needs any
of this?  What will it be used for?  What does it actually do?

thanks,

greg k-h