linux-kernel - Re: [PATCH v3 1/5] rust: miscdevice: Provide accessor to pull out miscdevice::this

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Message-ID: <20241206072025.GF8882@google.com>
Date: Fri, 6 Dec 2024 07:20:25 +0000
From: Lee Jones <lee@...nel.org>
To: Fiona Behrens <me@...enk.dev>
Cc: linux-kernel@...r.kernel.org, arnd@...db.de, gregkh@...uxfoundation.org,
	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 1/5] rust: miscdevice: Provide accessor to pull out
 miscdevice::this_device

On Thu, 05 Dec 2024, Fiona Behrens wrote:

> 
> 
> On 5 Dec 2024, at 17:25, Lee Jones wrote:
> 
> > There are situations where a pointer to a `struct device` will become
> > necessary (e.g. for calling into dev_*() functions).  This accessor
> > allows callers to pull this out from the `struct miscdevice`.
> >
> > Signed-off-by: Lee Jones <lee@...nel.org>
> > ---
> >  rust/kernel/miscdevice.rs | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/rust/kernel/miscdevice.rs b/rust/kernel/miscdevice.rs
> > index 7e2a79b3ae26..55340f316006 100644
> > --- a/rust/kernel/miscdevice.rs
> > +++ b/rust/kernel/miscdevice.rs
> > @@ -10,11 +10,13 @@
> >
> >  use crate::{
> >      bindings,
> > +    device::Device,
> >      error::{to_result, Error, Result, VTABLE_DEFAULT_ERROR},
> >      prelude::*,
> >      str::CStr,
> >      types::{ForeignOwnable, Opaque},
> >  };
> > +
> >  use core::{
> >      ffi::{c_int, c_long, c_uint, c_ulong},
> >      marker::PhantomData,
> > @@ -84,6 +86,13 @@ pub fn register(opts: MiscDeviceOptions) -> impl PinInit<Self, Error> {
> >      pub fn as_raw(&self) -> *mut bindings::miscdevice {
> >          self.inner.get()
> >      }
> > +
> > +    /// Returns a pointer to the current Device
> 
> I would not call this pointer but rather reference? Pointer is usually associated with *mut or *const, and this is a reference to the Device abstraction

No, no, my Rustacean friend.  That's not the point of the comment at
all.  We can all see that it the return value is literally a reference
to Device (&Device), but the thing it's actually passing back is a
`struct device *`:

  % git --no-pager grep -n this_device -- include/
  include/linux/miscdevice.h:85:	struct device *this_device;

I'll change the comment to be a lot more intentional.

-- 
Lee Jones [李琼斯]