[PATCH v11 7/8] rust: Add read_poll_timeout functions

FUJITA Tomonori
2025-02-20T07:11:09Z

Add read_poll_timeout functions which poll periodically until a
condition is met or a timeout is reached.

The C's read_poll_timeout (include/linux/iopoll.h) is a complicated
macro and a simple wrapper for Rust doesn't work. So this implements
the same functionality in Rust.

The C version uses usleep_range() while the Rust version uses
fsleep(), which uses the best sleep method so it works with spans that
usleep_range() doesn't work nicely with.

The sleep_before_read argument isn't supported since there is no user
for now. It's rarely used in the C version.

read_poll_timeout() can only be used in a nonatomic context. This
requirement is not checked by these abstractions, but it is intended
that klint [1] or a similar tool will be used to check it in the
future.

Link: https://rust-for-linux.com/klint [1]
Tested-by: Daniel Almeida <daniel.almeida@collabora.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
---
rust/helpers/helpers.c | 1 +
rust/helpers/kernel.c | 18 +++++++
rust/kernel/cpu.rs | 13 +++++
rust/kernel/error.rs | 1 +
rust/kernel/io.rs | 2 +
rust/kernel/io/poll.rs | 120 +++++++++++++++++++++++++++++++++++++++++
rust/kernel/lib.rs | 1 +
7 files changed, 156 insertions(+)
create mode 100644 rust/helpers/kernel.c
create mode 100644 rust/kernel/cpu.rs
create mode 100644 rust/kernel/io/poll.rs

diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index 9565485a1a54..16d256897ccb 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -14,6 +14,7 @@
#include "cred.c"
#include "device.c"
#include "err.c"
+#include "kernel.c"
#include "fs.c"
#include "io.c"
#include "jump_label.c"
diff --git a/rust/helpers/kernel.c b/rust/helpers/kernel.c
new file mode 100644
index 000000000000..f04c04d4cc4f
--- /dev/null
+++ b/rust/helpers/kernel.c
@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/kernel.h>
+
+void rust_helper_cpu_relax(void)
+{
+ cpu_relax();
+}
+
+void rust_helper___might_sleep_precision(const char *file, int len, int line)
+{
+ __might_sleep_precision(file, len, line);
+}
+
+void rust_helper_might_resched(void)
+{
+ might_resched();
+}
diff --git a/rust/kernel/cpu.rs b/rust/kernel/cpu.rs
new file mode 100644
index 000000000000..eeeff4be84fa
--- /dev/null
+++ b/rust/kernel/cpu.rs
@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Processor related primitives.
+//!
+//! C header: [`include/linux/processor.h`](srctree/include/linux/processor.h).
+
+/// Lower CPU power consumption or yield to a hyperthreaded twin processor.
+///
+/// It also happens to serve as a compiler barrier.
+pub fn cpu_relax() {
+ // SAFETY: FFI call.
+ unsafe { bindings::cpu_relax() }
+}
diff --git a/rust/kernel/error.rs b/rust/kernel/error.rs
index f6ecf09cb65f..8858eb13b3df 100644
--- a/rust/kernel/error.rs
+++ b/rust/kernel/error.rs
@@ -64,6 +64,7 @@ macro_rules! declare_err {
declare_err!(EPIPE, "Broken pipe.");
declare_err!(EDOM, "Math argument out of domain of func.");
declare_err!(ERANGE, "Math result not representable.");
+ declare_err!(ETIMEDOUT, "Connection timed out.");
declare_err!(ERESTARTSYS, "Restart the system call.");
declare_err!(ERESTARTNOINTR, "System call was interrupted by a signal and will be restarted.");
declare_err!(ERESTARTNOHAND, "Restart if no handler.");
diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
index d4a73e52e3ee..be63742f517b 100644
--- a/rust/kernel/io.rs
+++ b/rust/kernel/io.rs
@@ -7,6 +7,8 @@
use crate::error::{code::EINVAL, Result};
use crate::{bindings, build_assert};

+pub mod poll;
+
/// Raw representation of an MMIO region.
///
/// By itself, the existence of an instance of this structure does not provide any guarantees that
diff --git a/rust/kernel/io/poll.rs b/rust/kernel/io/poll.rs
new file mode 100644
index 000000000000..5977b2082cc6
--- /dev/null
+++ b/rust/kernel/io/poll.rs
@@ -0,0 +1,120 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! IO polling.
+//!
+//! C header: [`include/linux/iopoll.h`](srctree/include/linux/iopoll.h).
+
+use crate::{
+ cpu::cpu_relax,
+ error::{code::*, Result},
+ time::{delay::fsleep, Delta, Instant},
+};
+
+/// Polls periodically until a condition is met or a timeout is reached.
+///
+/// The function repeatedly executes the given operation `op` closure and
+/// checks its result using the condition closure `cond`.
+/// If `cond` returns `true`, the function returns successfully with the result of `op`.
+/// Otherwise, it waits for a duration specified by `sleep_delta`
+/// before executing `op` again.
+/// This process continues until either `cond` returns `true` or the timeout,
+/// specified by `timeout_delta`, is reached. If `timeout_delta` is `None`,
+/// polling continues indefinitely until `cond` evaluates to `true` or an error occurs.
+///
+/// # Examples
+///
+/// ```rust,ignore
+/// fn wait_for_hardware(dev: &mut Device) -> Result<()> {
+/// // The `op` closure reads the value of a specific status register.
+/// let op = || -> Result<u16> { dev.read_ready_register() };
+///
+/// // The `cond` closure takes a reference to the value returned by `op`
+/// // and checks whether the hardware is ready.
+/// let cond = |val: &u16| *val == HW_READY;
+///
+/// match read_poll_timeout(op, cond, Delta::from_millis(50), Some(Delta::from_secs(3))) {
+/// Ok(_) => {
+/// // The hardware is ready. The returned value of the `op`` closure isn't used.
+/// Ok(())
+/// }
+/// Err(e) => Err(e),
+/// }
+/// }
+/// ```
+///
+/// ```rust
+/// use kernel::io::poll::read_poll_timeout;
+/// use kernel::time::Delta;
+/// use kernel::sync::{SpinLock, new_spinlock};
+///
+/// let lock = KBox::pin_init(new_spinlock!(()), kernel::alloc::flags::GFP_KERNEL)?;
+/// let g = lock.lock();
+/// read_poll_timeout(|| Ok(()), |()| true, Delta::from_micros(42), Some(Delta::from_micros(42)));
+/// drop(g);
+///
+/// # Ok::<(), Error>(())
+/// ```
+#[track_caller]
+pub fn read_poll_timeout<Op, Cond, T>(
+ mut op: Op,
+ mut cond: Cond,
+ sleep_delta: Delta,
+ timeout_delta: Option<Delta>,
+) -> Result<T>
+where
+ Op: FnMut() -> Result<T>,
+ Cond: FnMut(&T) -> bool,
+{
+ let start = Instant::now();
+ let sleep = !sleep_delta.is_zero();
+
+ if sleep {
+ might_sleep();
+ }
+
+ loop {
+ let val = op()?;
+ if cond(&val) {
+ // Unlike the C version, we immediately return.
+ // We know the condition is met so we don't need to check again.
+ return Ok(val);
+ }
+ if let Some(timeout_delta) = timeout_delta {
+ if start.elapsed() > timeout_delta {
+ // Unlike the C version, we immediately return.
+ // We have just called `op()` so we don't need to call it again.
+ return Err(ETIMEDOUT);
+ }
+ }
+ if sleep {
+ fsleep(sleep_delta);
+ }
+ // fsleep() could be busy-wait loop so we always call cpu_relax().
+ cpu_relax();
+ }
+}
+
+/// Annotation for functions that can sleep.
+///
+/// Equivalent to the C side [`might_sleep()`], this function serves as
+/// a debugging aid and a potential scheduling point.
+///
+/// This function can only be used in a nonatomic context.
+#[track_caller]
+fn might_sleep() {
+ #[cfg(CONFIG_DEBUG_ATOMIC_SLEEP)]
+ {
+ let loc = core::panic::Location::caller();
+ // SAFETY: FFI call.
+ unsafe {
+ crate::bindings::__might_sleep_precision(
+ loc.file().as_ptr().cast(),
+ loc.file().len() as i32,
+ loc.line() as i32,
+ )
+ }
+ }
+
+ // SAFETY: FFI call.
+ unsafe { crate::bindings::might_resched() }
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 496ed32b0911..415c500212dd 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -40,6 +40,7 @@
pub mod block;
#[doc(hidden)]
pub mod build_assert;
+pub mod cpu;
pub mod cred;
pub mod device;
pub mod device_id;
--
2.43.0