linux-kernel - [PATCH v1 4/7] rust: workqueue: define built-in queues

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Date:   Wed, 17 May 2023 20:31:16 +0000
From:   Alice Ryhl <aliceryhl@...gle.com>
To:     rust-for-linux@...r.kernel.org
Cc:     Miguel Ojeda <ojeda@...nel.org>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Tejun Heo <tj@...nel.org>,
        Lai Jiangshan <jiangshanlai@...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>,
        Benno Lossin <benno.lossin@...ton.me>,
        Alice Ryhl <aliceryhl@...gle.com>,
        linux-kernel@...r.kernel.org, patches@...ts.linux.dev
Subject: [PATCH v1 4/7] rust: workqueue: define built-in queues

From: Wedson Almeida Filho <walmeida@...rosoft.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@...rosoft.com>
Co-developed-by: Alice Ryhl <aliceryhl@...gle.com>
Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
---
 rust/kernel/workqueue.rs | 65 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)

diff --git a/rust/kernel/workqueue.rs b/rust/kernel/workqueue.rs
index e66b6b50dfae..22205d3bda72 100644
--- a/rust/kernel/workqueue.rs
+++ b/rust/kernel/workqueue.rs
@@ -97,3 +97,68 @@ pub unsafe trait WorkItem {
     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) }
+}
-- 
2.40.1.606.ga4b1b128d6-goog