[v2,4/8] rust: workqueue: define built-in queues

  From: Wedson Almeida Filho <walmeida@microsoft.com>

We provide these methods because it lets us access these queues from
Rust without using unsafe code.

These methods return `&'static Queue`. References annotated with the
'static lifetime are used when the referent will stay alive forever.
That is ok for these queues because they are global variables and cannot
be destroyed.

Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
Co-developed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
---
 rust/kernel/workqueue.rs | 65 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)
  

On Thu,  1 Jun 2023 13:49:42 +0000
Alice Ryhl <aliceryhl@google.com> wrote:

> From: Wedson Almeida Filho <walmeida@microsoft.com>
> 
> We provide these methods because it lets us access these queues from
> Rust without using unsafe code.
> 
> These methods return `&'static Queue`. References annotated with the
> 'static lifetime are used when the referent will stay alive forever.
> That is ok for these queues because they are global variables and cannot
> be destroyed.
> 
> Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
> Co-developed-by: Alice Ryhl <aliceryhl@google.com>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>

This looks fine to me, so:

Reviewed-by: Gary Guo <gary@garyguo.net>

Just one question about style: would people prefer:

	kernel::workqueue::system().enqueue(...)

or

	use kernel::workqueue::Queue;
	Queue::system().enqueue(...)

?

> ---
>  rust/kernel/workqueue.rs | 65 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 65 insertions(+)
> 
> diff --git a/rust/kernel/workqueue.rs b/rust/kernel/workqueue.rs
> index 9c630840039b..e37820f253f6 100644
> --- a/rust/kernel/workqueue.rs
> +++ b/rust/kernel/workqueue.rs
> @@ -105,3 +105,68 @@ unsafe fn __enqueue<F>(self, queue_work_on: F) -> Self::EnqueueOutput
>      where
>          F: FnOnce(*mut bindings::work_struct) -> bool;
>  }
> +
> +/// Returns the system work queue (`system_wq`).
> +///
> +/// It is the one used by `schedule[_delayed]_work[_on]()`. Multi-CPU multi-threaded. There are
> +/// users which expect relatively short queue flush time.
> +///
> +/// Callers shouldn't queue work items which can run for too long.
> +pub fn system() -> &'static Queue {
> +    // SAFETY: `system_wq` is a C global, always available.
> +    unsafe { Queue::from_raw(bindings::system_wq) }
> +}
> +
> +/// Returns the system high-priority work queue (`system_highpri_wq`).
> +///
> +/// It is similar to the one returned by [`system`] but for work items which require higher
> +/// scheduling priority.
> +pub fn system_highpri() -> &'static Queue {
> +    // SAFETY: `system_highpri_wq` is a C global, always available.
> +    unsafe { Queue::from_raw(bindings::system_highpri_wq) }
> +}
> +
> +/// Returns the system work queue for potentially long-running work items (`system_long_wq`).
> +///
> +/// It is similar to the one returned by [`system`] but may host long running work items. Queue
> +/// flushing might take relatively long.
> +pub fn system_long() -> &'static Queue {
> +    // SAFETY: `system_long_wq` is a C global, always available.
> +    unsafe { Queue::from_raw(bindings::system_long_wq) }
> +}
> +
> +/// Returns the system unbound work queue (`system_unbound_wq`).
> +///
> +/// Workers are not bound to any specific CPU, not concurrency managed, and all queued work items
> +/// are executed immediately as long as `max_active` limit is not reached and resources are
> +/// available.
> +pub fn system_unbound() -> &'static Queue {
> +    // SAFETY: `system_unbound_wq` is a C global, always available.
> +    unsafe { Queue::from_raw(bindings::system_unbound_wq) }
> +}
> +
> +/// Returns the system freezable work queue (`system_freezable_wq`).
> +///
> +/// It is equivalent to the one returned by [`system`] except that it's freezable.
> +pub fn system_freezable() -> &'static Queue {
> +    // SAFETY: `system_freezable_wq` is a C global, always available.
> +    unsafe { Queue::from_raw(bindings::system_freezable_wq) }
> +}
> +
> +/// Returns the system power-efficient work queue (`system_power_efficient_wq`).
> +///
> +/// It is inclined towards saving power and is converted to "unbound" variants if the
> +/// `workqueue.power_efficient` kernel parameter is specified; otherwise, it is similar to the one
> +/// returned by [`system`].
> +pub fn system_power_efficient() -> &'static Queue {
> +    // SAFETY: `system_power_efficient_wq` is a C global, always available.
> +    unsafe { Queue::from_raw(bindings::system_power_efficient_wq) }
> +}
> +
> +/// Returns the system freezable power-efficient work queue (`system_freezable_power_efficient_wq`).
> +///
> +/// It is similar to the one returned by [`system_power_efficient`] except that is freezable.
> +pub fn system_freezable_power_efficient() -> &'static Queue {
> +    // SAFETY: `system_freezable_power_efficient_wq` is a C global, always available.
> +    unsafe { Queue::from_raw(bindings::system_freezable_power_efficient_wq) }
> +}
  

On 6/1/23 14:30, Gary Guo wrote:
> On Thu,  1 Jun 2023 13:49:42 +0000
> Alice Ryhl <aliceryhl@google.com> wrote:
> 
>> From: Wedson Almeida Filho <walmeida@microsoft.com>
>>
>> We provide these methods because it lets us access these queues from
>> Rust without using unsafe code.
>>
>> These methods return `&'static Queue`. References annotated with the
>> 'static lifetime are used when the referent will stay alive forever.
>> That is ok for these queues because they are global variables and cannot
>> be destroyed.
>>
>> Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
>> Co-developed-by: Alice Ryhl <aliceryhl@google.com>
>> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
>> Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
> 
> This looks fine to me, so:
> 
> Reviewed-by: Gary Guo <gary@garyguo.net>
> 
> Just one question about style: would people prefer:
> 
> 	kernel::workqueue::system().enqueue(...)
> 
> or
> 
> 	use kernel::workqueue::Queue;
> 	Queue::system().enqueue(...)
> 
> ?

I can compare the first with `std::thread::spawn` and the second
with enqueuing an executor with a future. Both makes sense to me so
I can't decide.

> [...]
  

Gary Guo <gary@garyguo.net> writes:
> On Thu,  1 Jun 2023 13:49:42 +0000
> Alice Ryhl <aliceryhl@google.com> wrote:
>> From: Wedson Almeida Filho <walmeida@microsoft.com>
>> 
>> We provide these methods because it lets us access these queues from
>> Rust without using unsafe code.
>> 
>> These methods return `&'static Queue`. References annotated with the
>> 'static lifetime are used when the referent will stay alive forever.
>> That is ok for these queues because they are global variables and cannot
>> be destroyed.
>> 
>> Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
>> Co-developed-by: Alice Ryhl <aliceryhl@google.com>
>> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
>> Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
> 
> This looks fine to me, so:
> 
> Reviewed-by: Gary Guo <gary@garyguo.net>
> 
> Just one question about style: would people prefer:
> 
> 	kernel::workqueue::system().enqueue(...)
> 
> or
> 
> 	use kernel::workqueue::Queue;
> 	Queue::system().enqueue(...)
> 
> ?

I prefer the first version.

Alice
  

Alice Ryhl <aliceryhl@google.com> writes:

> From: Wedson Almeida Filho <walmeida@microsoft.com>
>
> We provide these methods because it lets us access these queues from
> Rust without using unsafe code.
>
> These methods return `&'static Queue`. References annotated with the
> 'static lifetime are used when the referent will stay alive forever.
> That is ok for these queues because they are global variables and cannot
> be destroyed.
>
> Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
> Co-developed-by: Alice Ryhl <aliceryhl@google.com>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>

I would suggest adding the description to freezable:

"A freezable wq participates in the freeze phase of the system suspend
operations. Work items on the wq are drained and no new work item starts
execution until thawed."

But otherwise 👍

Reviewed-by: Andreas Hindborg (Samsung) <nmi@metaspace.dk>

> ---
>  rust/kernel/workqueue.rs | 65 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 65 insertions(+)
>
> diff --git a/rust/kernel/workqueue.rs b/rust/kernel/workqueue.rs
> index 9c630840039b..e37820f253f6 100644
> --- a/rust/kernel/workqueue.rs
> +++ b/rust/kernel/workqueue.rs
> @@ -105,3 +105,68 @@ unsafe fn __enqueue<F>(self, queue_work_on: F) -> Self::EnqueueOutput
>      where
>          F: FnOnce(*mut bindings::work_struct) -> bool;
>  }
> +
> +/// Returns the system work queue (`system_wq`).
> +///
> +/// It is the one used by `schedule[_delayed]_work[_on]()`. Multi-CPU multi-threaded. There are
> +/// users which expect relatively short queue flush time.
> +///
> +/// Callers shouldn't queue work items which can run for too long.
> +pub fn system() -> &'static Queue {
> +    // SAFETY: `system_wq` is a C global, always available.
> +    unsafe { Queue::from_raw(bindings::system_wq) }
> +}
> +
> +/// Returns the system high-priority work queue (`system_highpri_wq`).
> +///
> +/// It is similar to the one returned by [`system`] but for work items which require higher
> +/// scheduling priority.
> +pub fn system_highpri() -> &'static Queue {
> +    // SAFETY: `system_highpri_wq` is a C global, always available.
> +    unsafe { Queue::from_raw(bindings::system_highpri_wq) }
> +}
> +
> +/// Returns the system work queue for potentially long-running work items (`system_long_wq`).
> +///
> +/// It is similar to the one returned by [`system`] but may host long running work items. Queue
> +/// flushing might take relatively long.
> +pub fn system_long() -> &'static Queue {
> +    // SAFETY: `system_long_wq` is a C global, always available.
> +    unsafe { Queue::from_raw(bindings::system_long_wq) }
> +}
> +
> +/// Returns the system unbound work queue (`system_unbound_wq`).
> +///
> +/// Workers are not bound to any specific CPU, not concurrency managed, and all queued work items
> +/// are executed immediately as long as `max_active` limit is not reached and resources are
> +/// available.
> +pub fn system_unbound() -> &'static Queue {
> +    // SAFETY: `system_unbound_wq` is a C global, always available.
> +    unsafe { Queue::from_raw(bindings::system_unbound_wq) }
> +}
> +
> +/// Returns the system freezable work queue (`system_freezable_wq`).
> +///
> +/// It is equivalent to the one returned by [`system`] except that it's freezable.
> +pub fn system_freezable() -> &'static Queue {
> +    // SAFETY: `system_freezable_wq` is a C global, always available.
> +    unsafe { Queue::from_raw(bindings::system_freezable_wq) }
> +}
> +
> +/// Returns the system power-efficient work queue (`system_power_efficient_wq`).
> +///
> +/// It is inclined towards saving power and is converted to "unbound" variants if the
> +/// `workqueue.power_efficient` kernel parameter is specified; otherwise, it is similar to the one
> +/// returned by [`system`].
> +pub fn system_power_efficient() -> &'static Queue {
> +    // SAFETY: `system_power_efficient_wq` is a C global, always available.
> +    unsafe { Queue::from_raw(bindings::system_power_efficient_wq) }
> +}
> +
> +/// Returns the system freezable power-efficient work queue (`system_freezable_power_efficient_wq`).
> +///
> +/// It is similar to the one returned by [`system_power_efficient`] except that is freezable.
> +pub fn system_freezable_power_efficient() -> &'static Queue {
> +    // SAFETY: `system_freezable_power_efficient_wq` is a C global, always available.
> +    unsafe { Queue::from_raw(bindings::system_freezable_power_efficient_wq) }
> +}
  

On 01.06.23 15:49, Alice Ryhl wrote:
> From: Wedson Almeida Filho <walmeida@microsoft.com>
> 
> We provide these methods because it lets us access these queues from
> Rust without using unsafe code.
> 
> These methods return `&'static Queue`. References annotated with the
> 'static lifetime are used when the referent will stay alive forever.
> That is ok for these queues because they are global variables and cannot
> be destroyed.
> 
> Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
> Co-developed-by: Alice Ryhl <aliceryhl@google.com>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>

Reviewed-by: Benno Lossin <benno.lossin@proton.me>