Feedback-ID: iad51458e:Fastmail
Date:   Fri, 10 Mar 2023 10:56:31 -0800
From:   Boqun Feng <boqun.feng@gmail.com>
To:     Asahi Lina <lina@asahilina.net>
Cc:     Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Gary Guo <gary@garyguo.net>,
        =?iso-8859-1?Q?Bj=F6rn?= Roy Baron <bjorn3_gh@protonmail.com>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>,
        Luben Tuikov <luben.tuikov@amd.com>,
        Jarkko Sakkinen <jarkko@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Alyssa Rosenzweig <alyssa@rosenzweig.io>,
        Karol Herbst <kherbst@redhat.com>,
        Ella Stanforth <ella@iglunix.org>,
        Faith Ekstrand <faith.ekstrand@collabora.com>,
        Mary <mary@mary.zone>, linux-kernel@vger.kernel.org,
        dri-devel@lists.freedesktop.org, rust-for-linux@vger.kernel.org,
        linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org,
        linux-sgx@vger.kernel.org, asahi@lists.linux.dev
Subject: Re: [PATCH RFC 02/18] rust: drm: Add Device and Driver abstractions
Message-ID: <ZAt9X8qDUHQ/YnW8@boqun-archlinux>
References: <20230307-rust-drm-v1-0-917ff5bc80a8@asahilina.net>
 <20230307-rust-drm-v1-2-917ff5bc80a8@asahilina.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20230307-rust-drm-v1-2-917ff5bc80a8@asahilina.net>
Precedence: bulk

On Tue, Mar 07, 2023 at 11:25:27PM +0900, Asahi Lina wrote:
[...]
> +
> +// SAFETY: `Device` only holds a pointer to a C device, which is safe to be used from any thread.
> +unsafe impl<T: drm::drv::Driver> Send for Device<T> {}
> +
> +// SAFETY: `Device` only holds a pointer to a C device, references to which are safe to be used
> +// from any thread.
> +unsafe impl<T: drm::drv::Driver> Sync for Device<T> {}
> +

Here is the mind model I use to check whether a type is `Send` or
`Sync`

*	If an object of a type can be created on one thread and dropped
	on the another thread, then it's `Send`.

*	If multiple threads can call the immutable functions (i.e.
	functions with `&self`) of the same object of a type, then the
	it's `Sync`.

Maybe it's incomplete, but at least I find it useful to determine
whether a type is `Send` or `Sync`: it's not just the struct
representation, the behaviors (functions) of the struct also matter.

If that looks reasonable to you, maybe update the "SAFETY" comments in
the future version? Thanks ;-)

(I know you brought this up in the meeting, sorry I guess I wasn't fully
woken when answering you ;-))

Regards,
Boqun

> +// Make drm::Device work for dev_info!() and friends
> +unsafe impl<T: drm::drv::Driver> device::RawDevice for Device<T> {
> +    fn raw_device(&self) -> *mut bindings::device {
> +        // SAFETY: ptr must be valid per the type invariant
> +        unsafe { (*self.ptr).dev }
> +    }
> +}
[...]