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Date: Tue, 27 Jan 2026 21:07:37 +0100
Message-Id: <DFZN5P8G6MQG.2DYXNFSRIL450@kernel.org>
From: "Danilo Krummrich" <dakr@kernel.org>
Subject: Re: [PATCH v2 1/2] rust: introduce abstractions for fwctl
Cc: "Jason Gunthorpe" <jgg@nvidia.com>, <rust-for-linux@vger.kernel.org>,
 <linux-pci@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
 <aliceryhl@google.com>, <bhelgaas@google.com>, <kwilczynski@kernel.org>,
 <ojeda@kernel.org>, <alex.gaynor@gmail.com>, <boqun.feng@gmail.com>,
 <gary@garyguo.net>, <bjorn3_gh@protonmail.com>, <lossin@kernel.org>,
 <a.hindborg@kernel.org>, <tmgross@umich.edu>, <markus.probst@posteo.de>,
 <helgaas@kernel.org>, <cjia@nvidia.com>, <smitra@nvidia.com>,
 <ankita@nvidia.com>, <aniketa@nvidia.com>, <kwankhede@nvidia.com>,
 <targupta@nvidia.com>, <acourbot@nvidia.com>, <joelagnelf@nvidia.com>,
 <jhubbard@nvidia.com>, <zhiwang@kernel.org>, <daniel.almeida@collabora.com>
To: "Zhi Wang" <zhiw@nvidia.com>
References: <20260122204232.15988-1-zhiw@nvidia.com>
 <20260122204232.15988-2-zhiw@nvidia.com>
 <20260126181912.GA2131321@nvidia.com>
 <20260127215744.332380fe.zhiw@nvidia.com>
In-Reply-To: <20260127215744.332380fe.zhiw@nvidia.com>

On Tue Jan 27, 2026 at 8:57 PM CET, Zhi Wang wrote:
> The fwctl_alloc_device() helper allocates a raw struct fwctl_device
> without private driver data here. The Rust driver object should be
> already allocated and initialized separately before reaching this
> point.
>
> We rely on the standard dev->parent chain to access the rust driver
> object from the fwctl callbacks.

(I will go for a thorough review soon, but for now a quick drive-by comment=
.)

IIUC, you are saying that the user is supposed to use the private data of t=
he
parent device in fwctl callbacks. Let's not make this a design choice pleas=
e.
Instead, allow the user pass in separate private data for the fwctl device =
as
well.

This serves the purpose of clear ownership and lifetime of the data. E.g. t=
he
fwctl device does not necessarily exist as long as the parent device is bou=
nd.

It is a good thing if driver authors are forced to take a decision about wh=
ich
object owns the data and what's the scope of the data.