linux-kernel - Re: [PATCH v2 2/2] rust: miscdevice: add base miscdevice abstraction

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Message-Id: <bdb276f3-154c-4e1a-95ef-15f9c2745da3@app.fastmail.com>
Date: Wed, 02 Oct 2024 20:08:02 +0000
From: "Arnd Bergmann" <arnd@...db.de>
To: "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>
Cc: "Christian Brauner" <brauner@...nel.org>,
 "Alice Ryhl" <aliceryhl@...gle.com>, "Miguel Ojeda" <ojeda@...nel.org>,
 "Alexander Viro" <viro@...iv.linux.org.uk>, "Jan Kara" <jack@...e.cz>,
 "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>,
 "Trevor Gross" <tmgross@...ch.edu>, rust-for-linux@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] rust: miscdevice: add base miscdevice abstraction

On Wed, Oct 2, 2024, at 16:04, Greg Kroah-Hartman wrote:
> On Wed, Oct 02, 2024 at 03:45:08PM +0000, Arnd Bergmann wrote:
>> On Wed, Oct 2, 2024, at 14:23, Christian Brauner wrote:
>> 
>> Here, the 64-bit 'old' has the same size as the 32-bit 'new',
>> so if we try to handle them in a shared native/compat ioctl
>> function, this needs an extra in_conmpat_syscall() check that
>> adds complexity and is easy to forget.
>
> Agreed, "extending" ioctls is considered a bad thing and it's just
> easier to create a new one.  Or use some flags and reserved fields, if
> you remember to add them in the beginning...
>
> Anyway, this is all great, but for now, I'll take this series in my tree
> and we can add onto it from there.  I'll dig up some sample code that
> uses this too, so that we make sure it works properly.  Give me a few
> days to catch up before it lands in my trees...

Sounds good to me, it's clear we don't get a quick solution and
there is nothing stopping us from revisiting this after we have a
couple of drivers using ioctl.

      Arnd