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.

`sleep` functions including `fsleep` belongs to TIMERS, not
TIMEKEEPING. They are maintained separately. rust/kernel/time.rs is an
abstraction for TIMEKEEPING. To make Rust abstractions match the C
side, add rust/kernel/time/delay.rs for this wrapper.

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.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Link: https://rust-for-linux.com/klint [1]
---
 rust/helpers/helpers.c    |  1 +
 rust/helpers/time.c       |  8 ++++++++
 rust/kernel/time.rs       |  4 +++-
 rust/kernel/time/delay.rs | 31 +++++++++++++++++++++++++++++++
 4 files changed, 43 insertions(+), 1 deletion(-)
 create mode 100644 rust/helpers/time.c
 create mode 100644 rust/kernel/time/delay.rs

diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index 30f40149f3a9..c274546bcf78 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -21,6 +21,7 @@
 #include "slab.c"
 #include "spinlock.c"
 #include "task.c"
+#include "time.c"
 #include "uaccess.c"
 #include "wait.c"
 #include "workqueue.c"
diff --git a/rust/helpers/time.c b/rust/helpers/time.c
new file mode 100644
index 000000000000..7ae64ad8141d
--- /dev/null
+++ b/rust/helpers/time.c
@@ -0,0 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/delay.h>
+
+void rust_helper_fsleep(unsigned long usecs)
+{
+	fsleep(usecs);
+}
diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs
index 9b0537b63cf7..d58daff6f928 100644
--- a/rust/kernel/time.rs
+++ b/rust/kernel/time.rs
@@ -2,12 +2,14 @@
 
 //! Time related primitives.
 //!
-//! This module contains the kernel APIs related to time and timers that
+//! This module contains the kernel APIs related to time that
 //! have been ported or wrapped for usage by Rust code in the kernel.
 //!
 //! C header: [`include/linux/jiffies.h`](srctree/include/linux/jiffies.h).
 //! C header: [`include/linux/ktime.h`](srctree/include/linux/ktime.h).
 
+pub mod delay;
+
 /// The number of nanoseconds per microsecond.
 pub const NSEC_PER_USEC: i64 = bindings::NSEC_PER_USEC as i64;
 
diff --git a/rust/kernel/time/delay.rs b/rust/kernel/time/delay.rs
new file mode 100644
index 000000000000..dc7e2b3a0ab2
--- /dev/null
+++ b/rust/kernel/time/delay.rs
@@ -0,0 +1,31 @@
+// 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 crate::time;
+use core::ffi::c_ulong;
+
+/// Sleeps for a given duration at least.
+///
+/// Equivalent to the kernel's [`fsleep`], flexible sleep function,
+/// which automatically chooses the best sleep method based on a duration.
+///
+/// `Delta` must be longer than one microsecond.
+///
+/// This function can only be used in a nonatomic context.
+pub fn fsleep(delta: time::Delta) {
+    // SAFETY: FFI call.
+    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_nanos() + time::NSEC_PER_USEC - 1) / time::NSEC_PER_USEC) as c_ulong,
+        )
+    }
+}
-- 
2.43.0

> +/// This function can only be used in a nonatomic context.
> +pub fn fsleep(delta: time::Delta) {
> +    // SAFETY: FFI call.
> +    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_nanos() + time::NSEC_PER_USEC - 1) / time::NSEC_PER_USEC) as c_ulong,

You add a as_sec() helper, but then don't use it? If the helper does
not do what you want, maybe the helper is wrong? This is part of why
we say all APIs should have a user.

	Andrew

On Wed, Oct 16, 2024 at 5:54 AM FUJITA Tomonori
<fujita.tomonori@gmail.com> wrote:
>
> 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.
>
> `sleep` functions including `fsleep` belongs to TIMERS, not
> TIMEKEEPING. They are maintained separately. rust/kernel/time.rs is an
> abstraction for TIMEKEEPING. To make Rust abstractions match the C
> side, add rust/kernel/time/delay.rs for this wrapper.
>
> 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.
>
> Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
> Link: https://rust-for-linux.com/klint [1]
> ---
>  rust/helpers/helpers.c    |  1 +
>  rust/helpers/time.c       |  8 ++++++++
>  rust/kernel/time.rs       |  4 +++-
>  rust/kernel/time/delay.rs | 31 +++++++++++++++++++++++++++++++
>  4 files changed, 43 insertions(+), 1 deletion(-)
>  create mode 100644 rust/helpers/time.c
>  create mode 100644 rust/kernel/time/delay.rs
>
> diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
> index 30f40149f3a9..c274546bcf78 100644
> --- a/rust/helpers/helpers.c
> +++ b/rust/helpers/helpers.c
> @@ -21,6 +21,7 @@
>  #include "slab.c"
>  #include "spinlock.c"
>  #include "task.c"
> +#include "time.c"
>  #include "uaccess.c"
>  #include "wait.c"
>  #include "workqueue.c"
> diff --git a/rust/helpers/time.c b/rust/helpers/time.c
> new file mode 100644
> index 000000000000..7ae64ad8141d
> --- /dev/null
> +++ b/rust/helpers/time.c
> @@ -0,0 +1,8 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/delay.h>
> +
> +void rust_helper_fsleep(unsigned long usecs)
> +{
> +       fsleep(usecs);
> +}
> diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs
> index 9b0537b63cf7..d58daff6f928 100644
> --- a/rust/kernel/time.rs
> +++ b/rust/kernel/time.rs
> @@ -2,12 +2,14 @@
>
>  //! Time related primitives.
>  //!
> -//! This module contains the kernel APIs related to time and timers that
> +//! This module contains the kernel APIs related to time that
>  //! have been ported or wrapped for usage by Rust code in the kernel.
>  //!
>  //! C header: [`include/linux/jiffies.h`](srctree/include/linux/jiffies.h).
>  //! C header: [`include/linux/ktime.h`](srctree/include/linux/ktime.h).
>
> +pub mod delay;
> +
>  /// The number of nanoseconds per microsecond.
>  pub const NSEC_PER_USEC: i64 = bindings::NSEC_PER_USEC as i64;
>
> diff --git a/rust/kernel/time/delay.rs b/rust/kernel/time/delay.rs
> new file mode 100644
> index 000000000000..dc7e2b3a0ab2
> --- /dev/null
> +++ b/rust/kernel/time/delay.rs
> @@ -0,0 +1,31 @@
> +// 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 crate::time;
> +use core::ffi::c_ulong;
> +
> +/// Sleeps for a given duration at least.
> +///
> +/// Equivalent to the kernel's [`fsleep`], flexible sleep function,
> +/// which automatically chooses the best sleep method based on a duration.
> +///
> +/// `Delta` must be longer than one microsecond.

Why is this required? Right now you just round up to one microsecond,
which seems okay.

> +/// This function can only be used in a nonatomic context.
> +pub fn fsleep(delta: time::Delta) {
> +    // SAFETY: FFI call.
> +    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_nanos() + time::NSEC_PER_USEC - 1) / time::NSEC_PER_USEC) as c_ulong,

You probably want this:

delta.as_nanos().saturating_add(time::NSEC_PER_USEC - 1) / time::NSEC_PER_USEC

This would avoid a crash if someone passes i64::MAX nanoseconds and
CONFIG_RUST_OVERFLOW_CHECKS is enabled.

Alice

On Wed, 16 Oct 2024 10:29:12 +0200
Alice Ryhl <aliceryhl@google.com> wrote:

>> diff --git a/rust/kernel/time/delay.rs b/rust/kernel/time/delay.rs
>> new file mode 100644
>> index 000000000000..dc7e2b3a0ab2
>> --- /dev/null
>> +++ b/rust/kernel/time/delay.rs
>> @@ -0,0 +1,31 @@
>> +// 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 crate::time;
>> +use core::ffi::c_ulong;
>> +
>> +/// Sleeps for a given duration at least.
>> +///
>> +/// Equivalent to the kernel's [`fsleep`], flexible sleep function,
>> +/// which automatically chooses the best sleep method based on a duration.
>> +///
>> +/// `Delta` must be longer than one microsecond.
> 
> Why is this required? Right now you just round up to one microsecond,
> which seems okay.

Oops, it should have been removed.

>> +/// This function can only be used in a nonatomic context.
>> +pub fn fsleep(delta: time::Delta) {
>> +    // SAFETY: FFI call.
>> +    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_nanos() + time::NSEC_PER_USEC - 1) / time::NSEC_PER_USEC) as c_ulong,
> 
> You probably want this:
> 
> delta.as_nanos().saturating_add(time::NSEC_PER_USEC - 1) / time::NSEC_PER_USEC
> 
> This would avoid a crash if someone passes i64::MAX nanoseconds and
> CONFIG_RUST_OVERFLOW_CHECKS is enabled.

Ah, I'll fix.

Thanks!

On Wed, Oct 16, 2024 at 10:29 AM Alice Ryhl <aliceryhl@google.com> wrote:
>
> You probably want this:
>
> delta.as_nanos().saturating_add(time::NSEC_PER_USEC - 1) / time::NSEC_PER_USEC
>
> This would avoid a crash if someone passes i64::MAX nanoseconds and
> CONFIG_RUST_OVERFLOW_CHECKS is enabled.

I think we should document whether `fsleep` is expected to be usable
for "forever" values.

It sounds like that, given "too large" values in `msecs_to_jiffies`
mean "infinite timeout".

Cheers,
Miguel

On Wed, 16 Oct 2024 11:42:07 +0200
Miguel Ojeda <miguel.ojeda.sandonis@gmail.com> wrote:

> On Wed, Oct 16, 2024 at 10:29 AM Alice Ryhl <aliceryhl@google.com> wrote:
>>
>> You probably want this:
>>
>> delta.as_nanos().saturating_add(time::NSEC_PER_USEC - 1) / time::NSEC_PER_USEC
>>
>> This would avoid a crash if someone passes i64::MAX nanoseconds and
>> CONFIG_RUST_OVERFLOW_CHECKS is enabled.
> 
> I think we should document whether `fsleep` is expected to be usable
> for "forever" values.
> 
> It sounds like that, given "too large" values in `msecs_to_jiffies`
> mean "infinite timeout".

Do you mean msecs_to_jiffies() returns MAX_JIFFY_OFFSET ((LONG_MAX >>
1)-1) with a value exceeding i32::MAX milliseconds?

On Thu, Oct 24, 2024 at 2:22 AM FUJITA Tomonori
<fujita.tomonori@gmail.com> wrote:
>
> Do you mean msecs_to_jiffies() returns MAX_JIFFY_OFFSET ((LONG_MAX >>
> 1)-1) with a value exceeding i32::MAX milliseconds?

Yeah -- well, I was referring to its docs:

 * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
 *
 * - 'too large' values [that would result in larger than
 *   MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.

So I assume `fsleep` is meant to inherit that.

Cheers,
Miguel