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From:   Alice Ryhl <aliceryhl@google.com>
Date:   Fri, 8 Dec 2023 08:43:25 +0100
Message-ID: <CAH5fLghg7=eF38fNeUTEFe9zH95H-Que_911kJ+g_rsNrODHsw@mail.gmail.com>
Subject: Re: [PATCH v2 4/7] rust: file: add `FileDescriptorReservation`
To:     Benno Lossin <benno.lossin@proton.me>
Cc:     Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        =?UTF-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>,
        Andreas Hindborg <a.hindborg@samsung.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <brauner@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        =?UTF-8?B?QXJ2ZSBIasO4bm5ldsOlZw==?= <arve@android.com>,
        Todd Kjos <tkjos@android.com>,
        Martijn Coenen <maco@android.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Carlos Llamas <cmllamas@google.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Kees Cook <keescook@chromium.org>,
        Matthew Wilcox <willy@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Daniel Xu <dxu@dxuuu.xyz>, linux-kernel@vger.kernel.org,
        rust-for-linux@vger.kernel.org, linux-fsdevel@vger.kernel.org
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On Fri, Dec 8, 2023 at 8:37=E2=80=AFAM Benno Lossin <benno.lossin@proton.me=
> wrote:
> > +/// Zero-sized type to mark types not [`Send`].
> > +///
> > +/// Add this type as a field to your struct if your type should not be=
 sent to a different task.
> > +/// Since [`Send`] is an auto trait, adding a single field that is `!S=
end` will ensure that the
> > +/// whole type is `!Send`.
> > +///
> > +/// If a type is `!Send` it is impossible to give control over an inst=
ance of the type to another
> > +/// task. This is useful when a type stores task-local information for=
 example file descriptors.
> > +pub type NotThreadSafe =3D PhantomData<*mut ()>;
>
> This should be in its own commit.

Will do.

> Then you can also change the usages of `PhantomData<*mut ()>` in
> `Guard` and `TaskRef`.

Will do.

> It would be nice to use `NotThreadSafe` as the value instead of
> `PhantomData`, since it is a bit confusing...

That doesn't compile, unfortunately.

> I think we might be able to also have a constant with the same name
> that is just `pub const NotThreadSafe: NotThreadSafe =3D PhantomData;`.

I can try to get this to work, but I worry that they will shadow each other=
.

Alice