linux-kernel - Re: [PATCH 0/3] rust: miscdevice: Add additional data to MiscDeviceRegistration

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Message-ID: <2025012210-curry-gratified-a614@gregkh>
Date: Wed, 22 Jan 2025 10:22:23 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Christian Schrefl <chrisi.schrefl@...il.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 <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
	Arnd Bergmann <arnd@...db.de>, Lee Jones <lee@...nel.org>,
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] rust: miscdevice: Add additional data to
 MiscDeviceRegistration

On Tue, Jan 21, 2025 at 11:29:40AM +0100, Christian Schrefl wrote:
> 
> On 20.01.25 6:46 AM, Greg Kroah-Hartman wrote:
> > On Sun, Jan 19, 2025 at 11:11:12PM +0100, Christian Schrefl wrote:
> >> This set is based on Greg's driver-core-next tree.
> >>
> >> Currently there is no good way to pass arbitrary data from the driver to
> >> a miscdevice or to share data between individual handles to a miscdevice in rust.
> > 
> > Why would you want to do this?  A misc device instance should be "self
> > contained" with the needed stuff to make it work.
> > 
> > Do you have an example of where this is needed as I can't figure out the
> > goal here, sorry.
> 
> The main reason for needing this was that I could not figure out how to otherwise
> use a Devres from the platfrom driver probe in the implementation of the miscdevice.

A platform device has nothing to do with a misc device.  They should be
separate as they have totally different lifecycles.

> The reason to add this to MiscDeviceRegistration is to avoid race-conditions between
> the fops and driver registration/deregistration.
> (See the commit description of patch 2/3)
> 
> If there is a better or more intended way to achieve that please let me know.

I think you need an object that contains both of these, the driver_data
pointer field for the misc device should be able to be used for this,
right?

thanks,

greg k-h