linux-kernel - Re: [PATCH v8 0/4] rust: replace kernel::str::CStr w/ core::ffi::CStr

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Message-ID: <CAH5fLgjnYrfqmsv+nFpBr=cNHosfzY2VRzVU=Zn_PwPe8Ww=0g@mail.gmail.com>
Date: Thu, 20 Feb 2025 19:48:48 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Tamir Duberstein <tamird@...il.com>
Cc: Michal Rostecki <vadorovsky@...tonmail.com>, Miguel Ojeda <ojeda@...nel.org>, 
	Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>, 
	Gary Guo <gary@...yguo.net>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Trevor Gross <tmgross@...ch.edu>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 0/4] rust: replace kernel::str::CStr w/ core::ffi::CStr

On Wed, Feb 19, 2025 at 2:33 PM Tamir Duberstein <tamird@...il.com> wrote:
>
> On Wed, Feb 19, 2025 at 9:21 AM Alice Ryhl <aliceryhl@...gle.com> wrote:
> >
> > On Tue, Feb 18, 2025 at 5:05 PM Tamir Duberstein <tamird@...il.com> wrote:
> > >
> > > Gentle ping. Trevor, Alice, Benno: you all participated in the last
> > > round of review - I'd appreciate it if you could take a look at this
> > > series.
> >
> > The primary thing that comes to mind looking at this is that losing
> > the Display impl is pretty sad. Having to jump through hoops every
> > time you want to print a string isn't great :(
>
> There's the practical answer and the philosophical one. The former is
> that core::ffi::CStr doesn't impl Display. The latter is that Display
> implementations aren't meant to be lossy, and we shouldn't make it
> ergonomic to do things that might surprise the user.

I don't think there's any problem with a lossy Display impl. It's
supposed to be user-facing, and that's more or less what it requires.
Does kernel printing even require the string to be utf-8 in the first
place? I guess there's a mismatch about that here.

> We could add our own UnicodeCStr which could impl Display and be
> AsRef<CStr>. Do you think that should gate this work?

The solution I actually want is just for CStr to be Display, but
that's not something we can control on the kernel-side. I won't block
this change over it.

Alice