linux-kernel - Re: [PATCH rust-next v2 0/3] rust: miscdevice: add llseek support

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Message-ID: <aPEDoAXCqGxwPM5D@zeus>
Date: Thu, 16 Oct 2025 23:39:28 +0900
From: Ryosuke Yasuoka <ryasuoka@...hat.com>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: arnd@...db.de, ojeda@...nel.org, alex.gaynor@...il.com,
	boqun.feng@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com,
	lossin@...nel.org, a.hindborg@...nel.org, aliceryhl@...gle.com,
	tmgross@...ch.edu, dakr@...nel.org, viro@...iv.linux.org.uk,
	brauner@...nel.org, jack@...e.cz, rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH rust-next v2 0/3] rust: miscdevice: add llseek support

On Thu, Oct 16, 2025 at 01:24:12PM +0200, Greg KH wrote:
> On Thu, Oct 16, 2025 at 07:19:51PM +0900, Ryosuke Yasuoka wrote:
> > On Wed, Oct 15, 2025 at 07:40:12AM +0200, Greg KH wrote:
> > > On Wed, Oct 15, 2025 at 01:02:40PM +0900, Ryosuke Yasuoka wrote:
> > > > Hi all,
> > > > 
> > > > This patch series add support for the llseek file operation to misc
> > > > devices written in Rust.
> > > 
> > > Cool, but what miscdevice driver needs llseek support?  Do you have a
> > > real user for this that we can see as well?
> > 
> > Currently no. Because lseek is one of fundamental functions for device
> > driver, I think it's valuable to add support. I believe we'll have real
> > users based on read, write, and this lseek support.
> 
> Char devices that use lseek are "odd", don't you agree?  There are no
> such current users under drivers/misc/ and only a rare few under
> drivers/char/ (the huge user of that is mem.c but we aren't going to be
> reimplementing that in rust any time soon...)
> 
> So without a real user of this api, I suggest we hold-off on adding it.
> Let's not add it until someone comes up with a very valid reason for it.

Thank you for your review and clear explanation.

I understand your point. It makes sense not to add this without real
user. I'll hold off on this and will revisit it if a concrete use case
emerges.

Best regards,
Ryosuke

> thanks,
> 
> greg k-h
>