linux-kernel - Re: [PATCH v3 0/5] rust: miscdevice: Provide sample driver using the new MiscDevice bindings

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Message-ID: <20241206074443.GJ8882@google.com>
Date: Fri, 6 Dec 2024 07:44:43 +0000
From: Lee Jones <lee@...nel.org>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: linux-kernel@...r.kernel.org, arnd@...db.de, ojeda@...nel.org,
	alex.gaynor@...il.com, boqun.feng@...il.com, gary@...yguo.net,
	bjorn3_gh@...tonmail.com, benno.lossin@...ton.me,
	a.hindborg@...nel.org, aliceryhl@...gle.com, tmgross@...ch.edu,
	rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v3 0/5] rust: miscdevice: Provide sample driver using the
 new MiscDevice bindings

On Fri, 06 Dec 2024, Greg KH wrote:

> On Thu, Dec 05, 2024 at 04:25:17PM +0000, Lee Jones wrote:
> > It has been suggested that the driver should use dev_info() instead of
> > pr_info() however there is currently no scaffolding to successfully pull
> > a 'struct device' out from driver data post register().  This is being
> > worked on and we will convert this over in due course.
> 
> But the miscdevice.rs change provides this to you, right?  Or if not,
> why not?

This does allow us to pull the 'struct device *` out from `struct
miscdevice`; however, since this resides in MiscDeviceRegistration,
which we lose access to after .init, we have no means to call it.

Alice is going to work on a way to use ThisModule to get the
MiscDeviceRegistration reference back from anywhere in the module. Until
that piece lands, we can't call MiscDeviceRegistration::device() outside
of RustMiscDeviceModule.

One option that I investigated involved global mutable variable that we
could store the &Device into during MiscDeviceRegistration, however this
got messy (actually just bloaty) fast.  Alice's solution will be
cleaner and more universally useful.

-- 
Lee Jones [李琼斯]