Commit d4b29ddf authored by FUJITA Tomonori's avatar FUJITA Tomonori Committed by Andreas Hindborg
Browse files

rust: time: Add wrapper for fsleep() function 

Add a wrapper for fsleep(), flexible sleep functions in
include/linux/delay.h which typically deals with hardware delays.

The kernel supports several sleep functions to handle various lengths
of delay. This adds fsleep(), automatically chooses the best sleep
method based on a duration.

fsleep() 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]
Reviewed-by: default avatarGary Guo <gary@garyguo.net>
Reviewed-by: default avatarAlice Ryhl <aliceryhl@google.com>
Reviewed-by: default avatarFiona Behrens <me@kloenk.dev>
Tested-by: default avatarDaniel Almeida <daniel.almeida@collabora.com>
Reviewed-by: default avatarAndreas Hindborg <a.hindborg@kernel.org>
Signed-off-by: default avatarFUJITA Tomonori <fujita.tomonori@gmail.com>
Link: https://lore.kernel.org/r/20250617144155.3903431-3-fujita.tomonori@gmail.com


Signed-off-by: default avatarAndreas Hindborg <a.hindborg@kernel.org>
parent fc38b7ff

rust/helpers/time.c

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// SPDX-License-Identifier: GPL-2.0



#include <linux/delay.h>

#include <linux/ktime.h>

#include <linux/timekeeping.h>



void rust_helper_fsleep(unsigned long usecs)

{

	fsleep(usecs);

}



ktime_t rust_helper_ktime_get_real(void)

{

	return ktime_get_real();

rust/kernel/time.rs

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@@ -26,6 +26,7 @@ 


use core::marker::PhantomData;



pub mod delay;

pub mod hrtimer;



/// The number of nanoseconds per microsecond.

rust/kernel/time/delay.rs

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// SPDX-License-Identifier: GPL-2.0



//! Delay and sleep primitives.

//!

//! This module contains the kernel APIs related to delay and sleep that

//! have been ported or wrapped for usage by Rust code in the kernel.

//!

//! C header: [`include/linux/delay.h`](srctree/include/linux/delay.h).



use super::Delta;

use crate::prelude::*;



/// Sleeps for a given duration at least.

///

/// Equivalent to the C side [`fsleep()`], flexible sleep function,

/// which automatically chooses the best sleep method based on a duration.

///

/// `delta` must be within `[0, i32::MAX]` microseconds;

/// otherwise, it is erroneous behavior. That is, it is considered a bug

/// to call this function with an out-of-range value, in which case the function

/// will sleep for at least the maximum value in the range and may warn

/// in the future.

///

/// The behavior above differs from the C side [`fsleep()`] for which out-of-range

/// values mean "infinite timeout" instead.

///

/// This function can only be used in a nonatomic context.

///

/// [`fsleep()`]: https://docs.kernel.org/timers/delay_sleep_functions.html#c.fsleep

pub fn fsleep(delta: Delta) {

    // The maximum value is set to `i32::MAX` microseconds to prevent integer

    // overflow inside fsleep, which could lead to unintentional infinite sleep.

    const MAX_DELTA: Delta = Delta::from_micros(i32::MAX as i64);



    let delta = if (Delta::ZERO..=MAX_DELTA).contains(&delta) {

        delta

    } else {

        // TODO: Add WARN_ONCE() when it's supported.

        MAX_DELTA

    };



    // SAFETY: It is always safe to call `fsleep()` with any duration.

    unsafe {

        // Convert the duration to microseconds and round up to preserve

        // the guarantee; `fsleep()` sleeps for at least the provided duration,

        // but that it may sleep for longer under some circumstances.

        bindings::fsleep(delta.as_micros_ceil() as c_ulong)

    }

}