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Date: Mon, 06 Jul 2026 13:30:55 +0200
Message-Id: <DJRGD98J154Y.2MSNQJSXANX08@kernel.org>
To: "Alexandre Courbot" <acourbot@nvidia.com>
From: "Danilo Krummrich" <dakr@kernel.org>
Subject: Re: [PATCH v6 1/1] rust: introduce abstractions for fwctl
Cc: "Zhi Wang" <zhiw@nvidia.com>, <rust-for-linux@vger.kernel.org>,
 <linux-kernel@vger.kernel.org>, <jgg@nvidia.com>, <dave.jiang@intel.com>,
 <saeedm@nvidia.com>, <jic23@kernel.org>, <gary@garyguo.net>,
 <joelagnelf@nvidia.com>, <aliceryhl@google.com>, <kwilczynski@kernel.org>,
 <ojeda@kernel.org>, <alex.gaynor@gmail.com>, <boqun.feng@gmail.com>,
 <bjorn3_gh@protonmail.com>, <lossin@kernel.org>, <a.hindborg@kernel.org>,
 <tmgross@umich.edu>, <cjia@nvidia.com>, <smitra@nvidia.com>,
 <ankita@nvidia.com>, <aniketa@nvidia.com>, <kwankhede@nvidia.com>,
 <targupta@nvidia.com>, <kjaju@nvidia.com>, <alkumar@nvidia.com>,
 <jhubbard@nvidia.com>, <zhiwang@kernel.org>, <daniel.almeida@collabora.com>
References: <20260629150156.3169384-1-zhiw@nvidia.com>
 <20260629150156.3169384-2-zhiw@nvidia.com>
 <DJR76RV8NEKN.2MP5M9Z66U4TY@nvidia.com>
In-Reply-To: <DJR76RV8NEKN.2MP5M9Z66U4TY@nvidia.com>

On Mon Jul 6, 2026 at 6:19 AM CEST, Alexandre Courbot wrote:
>> +impl<'a, T: Operations> Registration<'a, T> {
>> +    /// Register a previously allocated fwctl device with the given reg=
istration data.
>> +    ///
>> +    /// The `reg_data` is owned by the registration and accessible duri=
ng callbacks via
>> +    /// `Device::registration_data_unchecked()`.
>> +    ///
>> +    /// # Safety
>> +    ///
>> +    /// Callers must not `mem::forget()` the returned [`Registration`] =
or otherwise prevent its
>> +    /// [`Drop`] implementation from running, since `fwctl_unregister` =
must be called before the
>> +    /// parent device is unbound.
>> +    ///
>> +    /// `dev` must be an unregistered [`Device`] that is not associated=
 with any live
>> +    /// [`Registration`], and no other thread may attempt to register t=
he same device concurrently.
>> +    pub unsafe fn new(
>> +        _parent: &'a device::Device<device::Bound>,
>
> Why do we need `_parent`? Is it to provide a proof that the parent
> device is bound by the time of registration? If so, there is an obvious
> loophole: this method will accept any bound device, not necessarily the
> actual parent that was passed to `Device::new`.
>
> We should either store an `ARef<device::Device>` in `fwctl::Device` to
> perform the check at runtime, or add a requirement in the `Safety`
> paragraph that `_parent` must be the actual parent, since the method is
> already `unsafe` anyway.

Neither is needed, the fwctl::Device already carries a parent device pointe=
r
(available through AsRef in Rust).

This function should just compare dev.as_ref() with parent (which I thought=
 was
already the case in a previous version).