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Date: Fri, 27 Jun 2025 01:19:53 +0200
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Cc: <gregkh@linuxfoundation.org>, <rafael@kernel.org>, <ojeda@kernel.org>,
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Subject: Re: [PATCH v4 5/5] rust: devres: implement register_release()
From: "Benno Lossin" <lossin@kernel.org>
To: "Danilo Krummrich" <dakr@kernel.org>, "Boqun Feng"
 <boqun.feng@gmail.com>
X-Mailer: aerc 0.20.1
References: <20250626200054.243480-1-dakr@kernel.org>
 <20250626200054.243480-6-dakr@kernel.org> <aF2vgthQlNA3BsCD@tardis.local>
 <aF2yA9TbeIrTg-XG@cassiopeiae>
In-Reply-To: <aF2yA9TbeIrTg-XG@cassiopeiae>

On Thu Jun 26, 2025 at 10:48 PM CEST, Danilo Krummrich wrote:
> On Thu, Jun 26, 2025 at 01:37:22PM -0700, Boqun Feng wrote:
>> On Thu, Jun 26, 2025 at 10:00:43PM +0200, Danilo Krummrich wrote:
>> > +/// [`Devres`]-releaseable resource.
>> > +///
>> > +/// Register an object implementing this trait with [`register_releas=
e`]. Its `release`
>> > +/// function will be called once the device is being unbound.
>> > +pub trait Release {
>> > +    /// The [`ForeignOwnable`] pointer type consumed by [`register_re=
lease`].
>> > +    type Ptr: ForeignOwnable;
>> > +
>> > +    /// Called once the [`Device`] given to [`register_release`] is u=
nbound.
>> > +    fn release(this: Self::Ptr);
>> > +}
>> > +
>>=20
>> I would like to point out the limitation of this design, say you have a
>> `Foo` that can ipml `Release`, with this, I think you could only support
>> either `Arc<Foo>` or `KBox<Foo>`. You cannot support both as the input
>> for `register_release()`. Maybe we want:
>>=20
>>     pub trait Release<Ptr: ForeignOwnable> {
>>         fn release(this: Ptr);
>>     }
>
> Good catch! I think this wasn't possible without ForeignOwnable::Target.

Hmm do we really need that? Normally you either store a type in a shared
or a non-shared manner and not both...

---
Cheers,
Benno