linux-kernel - Re: [PATCH v3 6/9] rust: workqueue: add helper for defining work

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Message-ID: <87msyisvmi.fsf@metaspace.dk>
Date:   Tue, 22 Aug 2023 20:24:04 +0200
From:   "Andreas Hindborg (Samsung)" <nmi@...aspace.dk>
To:     Benno Lossin <benno.lossin@...ton.me>
Cc:     Alice Ryhl <aliceryhl@...gle.com>, rust-for-linux@...r.kernel.org,
        Tejun Heo <tj@...nel.org>, Miguel Ojeda <ojeda@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        linux-kernel@...r.kernel.org, patches@...ts.linux.dev
Subject: Re: [PATCH v3 6/9] rust: workqueue: add helper for defining
 work_struct fields


Hi Benno,

Benno Lossin <benno.lossin@...ton.me> writes:

...

>> +/// Links for a work item.
>> +///
>> +/// This struct contains a function pointer to the `run` function from the [`WorkItemPointer`]
>> +/// trait, and defines the linked list pointers necessary to enqueue a work item in a workqueue.
>> +///
>> +/// Wraps the kernel's C `struct work_struct`.
>> +///
>> +/// This is a helper type used to associate a `work_struct` with the [`WorkItem`] that uses it.
>> +#[repr(transparent)]
>> +pub struct Work<T: ?Sized, const ID: u64 = 0> {
>> +    work: Opaque<bindings::work_struct>,
>> +    _inner: PhantomData<T>,
>
> Should this really be `PhantomData<T>`? Are you dropping `T`s in the 
> destructor of `Work<T>`? I do not think so `PhantomData<fn() -> Box<T>>`
> should do the trick.
>

Could you elaborate what is the issue in having `PhantomData<T>`?

BR Andreas