linux-kernel - Re: [PATCH] rust: miscdevice: Export vtable testing

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Message-ID: <2025062836-reactor-mandate-6712@gregkh>
Date: Sat, 28 Jun 2025 07:06:38 +0100
From: Greg KH <gregkh@...uxfoundation.org>
To: Matthew Maurer <mmaurer@...gle.com>
Cc: 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 <lossin@...nel.org>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
	Danilo Krummrich <dakr@...nel.org>,
	"Isaac J. Manjarres" <isaacmanjarres@...gle.com>,
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rust: miscdevice: Export vtable testing

On Fri, Jun 27, 2025 at 11:42:38PM +0000, Matthew Maurer wrote:
> A common pattern in the kernel is to test whether a file belongs to a
> particular driver by checking its `f_op` struct against an expected
> value. This provides a safe way to perform that test for `MiscDevice`
> implementations without needing to directly expose the vtable.

Ick, who does that?  And why?  Who cares within the kernel what driver
owns a fd as why would any driver ever be passed a fd that is not owned
by it?

I would like to see a real user first please, or point out some places
in the kernel today that does this so we can go and fix them up :)

thanks,

greg k-h