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

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.

Unlike the C version, __might_sleep() is used instead of might_sleep()
to show proper debug info; the file name and line
number. might_resched() could be added to match what the C version
does but this function works without it.

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

For the proper debug info, readx_poll_timeout() and __might_sleep()
are implemented as a macro. We could implement them as a normal
function if there is a clean way to get a null-terminated string
without allocation from core::panic::Location::file().

readx_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]
Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
---
 rust/helpers/helpers.c   |  1 +
 rust/helpers/kernel.c    | 13 ++++++
 rust/kernel/error.rs     |  1 +
 rust/kernel/io.rs        |  5 +++
 rust/kernel/io/poll.rs   | 95 ++++++++++++++++++++++++++++++++++++++++
 rust/kernel/lib.rs       |  2 +
 rust/kernel/processor.rs | 13 ++++++
 7 files changed, 130 insertions(+)
 create mode 100644 rust/helpers/kernel.c
 create mode 100644 rust/kernel/io.rs
 create mode 100644 rust/kernel/io/poll.rs
 create mode 100644 rust/kernel/processor.rs

diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index c274546bcf78..f9569ff1717e 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -12,6 +12,7 @@
 #include "build_assert.c"
 #include "build_bug.c"
 #include "err.c"
+#include "kernel.c"
 #include "kunit.c"
 #include "mutex.c"
 #include "page.c"
diff --git a/rust/helpers/kernel.c b/rust/helpers/kernel.c
new file mode 100644
index 000000000000..da847059260b
--- /dev/null
+++ b/rust/helpers/kernel.c
@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/kernel.h>
+
+void rust_helper_cpu_relax(void)
+{
+	cpu_relax();
+}
+
+void rust_helper___might_sleep(const char *file, int line)
+{
+	__might_sleep(file, line);
+}
diff --git a/rust/kernel/error.rs b/rust/kernel/error.rs
index 6f1587a2524e..d571b9587ed6 100644
--- a/rust/kernel/error.rs
+++ b/rust/kernel/error.rs
@@ -58,6 +58,7 @@ 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
new file mode 100644
index 000000000000..033f3c4e4adf
--- /dev/null
+++ b/rust/kernel/io.rs
@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Input and Output.
+
+pub mod poll;
diff --git a/rust/kernel/io/poll.rs b/rust/kernel/io/poll.rs
new file mode 100644
index 000000000000..a8caa08f86f2
--- /dev/null
+++ b/rust/kernel/io/poll.rs
@@ -0,0 +1,95 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! IO polling.
+//!
+//! C header: [`include/linux/iopoll.h`](srctree/include/linux/iopoll.h).
+
+use crate::{
+    error::{code::*, Result},
+    processor::cpu_relax,
+    time::{delay::fsleep, Delta, Instant},
+};
+
+/// Polls periodically until a condition is met or a timeout is reached.
+///
+/// Public but hidden since it should only be used from public macros.
+#[doc(hidden)]
+pub fn read_poll_timeout<Op, Cond, T: Copy>(
+    mut op: Op,
+    cond: Cond,
+    sleep_delta: Delta,
+    timeout_delta: Delta,
+) -> Result<T>
+where
+    Op: FnMut() -> Result<T>,
+    Cond: Fn(T) -> bool,
+{
+    let start = Instant::now();
+    let sleep = !sleep_delta.is_zero();
+    let timeout = !timeout_delta.is_zero();
+
+    let val = loop {
+        let val = op()?;
+        if cond(val) {
+            // Unlike the C version, we immediately return.
+            // We know a condition is met so we don't need to check again.
+            return Ok(val);
+        }
+        if timeout && start.elapsed() > timeout_delta {
+            // Should we return Err(ETIMEDOUT) here instead of call op() again
+            // without a sleep between? But we follow the C version. op() could
+            // take some time so might be worth checking again.
+            break op()?;
+        }
+        if sleep {
+            fsleep(sleep_delta);
+        }
+        // fsleep() could be busy-wait loop so we always call cpu_relax().
+        cpu_relax();
+    };
+
+    if cond(val) {
+        Ok(val)
+    } else {
+        Err(ETIMEDOUT)
+    }
+}
+
+/// Print debug information if it's called inside atomic sections.
+///
+/// Equivalent to the kernel's [`__might_sleep`].
+#[macro_export]
+macro_rules! __might_sleep {
+    () => {
+        #[cfg(CONFIG_DEBUG_ATOMIC_SLEEP)]
+        // SAFETY: FFI call.
+        unsafe {
+            $crate::bindings::__might_sleep(
+                c_str!(::core::file!()).as_char_ptr(),
+                ::core::line!() as i32,
+            )
+        }
+    };
+}
+
+/// Polls periodically until a condition is met or a timeout is reached.
+///
+/// `op` is called repeatedly until `cond` returns `true` or the timeout is
+///  reached. The return value of `op` is passed to `cond`.
+///
+/// `sleep_delta` is the duration to sleep between calls to `op`.
+/// If `sleep_delta` is less than one microsecond, the function will busy-wait.
+///
+/// `timeout_delta` is the maximum time to wait for `cond` to return `true`.
+///
+/// This macro can only be used in a nonatomic context.
+#[macro_export]
+macro_rules! readx_poll_timeout {
+    ($op:expr, $cond:expr, $sleep_delta:expr, $timeout_delta:expr) => {{
+        if !$sleep_delta.is_zero() {
+            $crate::__might_sleep!();
+        }
+
+        $crate::io::poll::read_poll_timeout($op, $cond, $sleep_delta, $timeout_delta)
+    }};
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 22a3bfa5a9e9..b775fd1c9be0 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -35,6 +35,7 @@
 #[cfg(CONFIG_RUST_FW_LOADER_ABSTRACTIONS)]
 pub mod firmware;
 pub mod init;
+pub mod io;
 pub mod ioctl;
 #[cfg(CONFIG_KUNIT)]
 pub mod kunit;
@@ -44,6 +45,7 @@
 pub mod page;
 pub mod prelude;
 pub mod print;
+pub mod processor;
 pub mod sizes;
 pub mod rbtree;
 mod static_assert;
diff --git a/rust/kernel/processor.rs b/rust/kernel/processor.rs
new file mode 100644
index 000000000000..eeeff4be84fa
--- /dev/null
+++ b/rust/kernel/processor.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() }
+}
-- 
2.43.0

On Fri, Nov 01 2024, FUJITA Tomonori <fujita.tomonori@gmail.com> wrote:

> For the proper debug info, readx_poll_timeout() and __might_sleep()
> are implemented as a macro. We could implement them as a normal
> function if there is a clean way to get a null-terminated string
> without allocation from core::panic::Location::file().

Would it be too much to hope for either a compiler flag or simply
default behaviour for having the backing, static store of the file!()
&str being guaranteed to be followed by a nul character? (Of course that
nul should not be counted in the slice's length). That would in general
increase interop with C code.

This is hardly the last place where Rust code would pass
Location::file() into C, and having to pass that as a (ptr,len) pair
always and updating the receiving C code to use %.*s seems like an
uphill battle, especially when the C code passes the const char* pointer
through a few layers before it is finally passed to a printf-like
function.

And creating the nul-terminated strings with c_str! needlessly doubles
the storage needed for the file names (unless the rust compiler is smart
enough to then re-use the c_str result for the backing store of the
file!() &str).

Rasmus

On Thu, Nov 7, 2024 at 1:50 PM Rasmus Villemoes <ravi@prevas.dk> wrote:
>
> Would it be too much to hope for either a compiler flag or simply
> default behaviour for having the backing, static store of the file!()
> &str being guaranteed to be followed by a nul character? (Of course that
> nul should not be counted in the slice's length). That would in general
> increase interop with C code.

Definitely -- please see the "`c_stringify!`, `c_concat!`, `c_file!`
macros" item in:

    https://github.com/Rust-for-Linux/linux/issues/514

Relatedly, for `Location`, there is "C string equivalents
(nul-terminated) for `core::panic::Location`.", with this ACP:

    https://github.com/rust-lang/libs-team/issues/466

Cheers,
Miguel

On Thu, Nov 7, 2024 at 1:50 PM Rasmus Villemoes <ravi@prevas.dk> wrote:
>
> On Fri, Nov 01 2024, FUJITA Tomonori <fujita.tomonori@gmail.com> wrote:
>
> > For the proper debug info, readx_poll_timeout() and __might_sleep()
> > are implemented as a macro. We could implement them as a normal
> > function if there is a clean way to get a null-terminated string
> > without allocation from core::panic::Location::file().
>
> Would it be too much to hope for either a compiler flag or simply
> default behaviour for having the backing, static store of the file!()
> &str being guaranteed to be followed by a nul character? (Of course that
> nul should not be counted in the slice's length). That would in general
> increase interop with C code.
>
> This is hardly the last place where Rust code would pass
> Location::file() into C, and having to pass that as a (ptr,len) pair
> always and updating the receiving C code to use %.*s seems like an
> uphill battle, especially when the C code passes the const char* pointer
> through a few layers before it is finally passed to a printf-like
> function.

This is actively being discussed at:
https://github.com/rust-lang/libs-team/issues/466

> And creating the nul-terminated strings with c_str! needlessly doubles
> the storage needed for the file names (unless the rust compiler is smart
> enough to then re-use the c_str result for the backing store of the
> file!() &str).

For the case of c_str!(file!()), the compiler should do the right
thing. Not via deduplication, but via removal of unused globals.

Alice

On Fri, Nov 01, 2024 at 10:01:20AM +0900, FUJITA Tomonori wrote:
> Add read_poll_timeout functions which poll periodically until a
> condition is met or a timeout is reached.
> 
> 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.
> 
> Unlike the C version, __might_sleep() is used instead of might_sleep()
> to show proper debug info; the file name and line
> number. might_resched() could be added to match what the C version
> does but this function works without it.
> 
> The sleep_before_read argument isn't supported since there is no user
> for now. It's rarely used in the C version.
> 
> For the proper debug info, readx_poll_timeout() and __might_sleep()
> are implemented as a macro. We could implement them as a normal
> function if there is a clean way to get a null-terminated string
> without allocation from core::panic::Location::file().
> 

So printk() actually support printing a string with a precison value,
that is: a format string "%.*s" would take two inputs, one for the length
and the other for the pointer to the string, for example you can do:

	char *msg = "hello";

	printk("%.*s\n", 5, msg);

This is similar to printf() in glibc [1].

If we add another __might_sleep_precision() which accepts a file name
length:

	void __might_sleep_precision(const char *file, int len, int line)

then we don't need to use macro here, I've attached a diff based
on your whole patchset, and it seems working.

Cc printk folks to if they know any limitation on using precision.

Regards,
Boqun

[1]: https://www.gnu.org/software/libc/manual/html_node/Output-Conversion-Syntax.html#Output-Conversion-Syntax

> readx_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]
> Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
> ---

--------------------------------------------->8
diff --git a/drivers/net/phy/qt2025.rs b/drivers/net/phy/qt2025.rs
index dabb772c468f..4d368ce80db6 100644
--- a/drivers/net/phy/qt2025.rs
+++ b/drivers/net/phy/qt2025.rs
@@ -18,7 +18,7 @@
     Driver,
 };
 use kernel::prelude::*;
-use kernel::readx_poll_timeout;
+use kernel::read_poll_timeout;
 use kernel::sizes::{SZ_16K, SZ_8K};
 use kernel::time::Delta;
 
@@ -95,7 +95,7 @@ fn probe(dev: &mut phy::Device) -> Result<()> {
         // The micro-controller will start running from SRAM.
         dev.write(C45::new(Mmd::PCS, 0xe854), 0x0040)?;
 
-        readx_poll_timeout!(
+        read_poll_timeout(
             || dev.read(C45::new(Mmd::PCS, 0xd7fd)),
             |val| val != 0x00 && val != 0x10,
             Delta::from_millis(50),
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index be2e8c0a187e..b405b0d19bac 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -87,6 +87,8 @@ extern int dynamic_might_resched(void);
 #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
 extern void __might_resched(const char *file, int line, unsigned int offsets);
 extern void __might_sleep(const char *file, int line);
+extern void __might_resched_precision(const char *file, int len, int line, unsigned int offsets);
+extern void __might_sleep_precision(const char *file, int len, int line);
 extern void __cant_sleep(const char *file, int line, int preempt_offset);
 extern void __cant_migrate(const char *file, int line);
 
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 43e453ab7e20..f872aa18eaf0 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8543,7 +8543,7 @@ void __init sched_init(void)
 
 #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
 
-void __might_sleep(const char *file, int line)
+void __might_sleep_precision(const char *file, int len, int line)
 {
 	unsigned int state = get_current_state();
 	/*
@@ -8557,7 +8557,14 @@ void __might_sleep(const char *file, int line)
 			(void *)current->task_state_change,
 			(void *)current->task_state_change);
 
-	__might_resched(file, line, 0);
+	__might_resched_precision(file, len, line, 0);
+}
+
+void __might_sleep(const char *file, int line)
+{
+	long len = strlen(file);
+
+	__might_sleep_precision(file, len, line);
 }
 EXPORT_SYMBOL(__might_sleep);
 
@@ -8582,7 +8589,7 @@ static inline bool resched_offsets_ok(unsigned int offsets)
 	return nested == offsets;
 }
 
-void __might_resched(const char *file, int line, unsigned int offsets)
+void __might_resched_precision(const char *file, int len, int line, unsigned int offsets)
 {
 	/* Ratelimiting timestamp: */
 	static unsigned long prev_jiffy;
@@ -8605,8 +8612,8 @@ void __might_resched(const char *file, int line, unsigned int offsets)
 	/* Save this before calling printk(), since that will clobber it: */
 	preempt_disable_ip = get_preempt_disable_ip(current);
 
-	pr_err("BUG: sleeping function called from invalid context at %s:%d\n",
-	       file, line);
+	pr_err("BUG: sleeping function called from invalid context at %.*s:%d\n",
+	       len, file, line);
 	pr_err("in_atomic(): %d, irqs_disabled(): %d, non_block: %d, pid: %d, name: %s\n",
 	       in_atomic(), irqs_disabled(), current->non_block_count,
 	       current->pid, current->comm);
@@ -8631,6 +8638,13 @@ void __might_resched(const char *file, int line, unsigned int offsets)
 	dump_stack();
 	add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
 }
+
+void __might_resched(const char *file, int line, unsigned int offsets)
+{
+	long len = strlen(file);
+
+	__might_resched_precision(file, len, line, offsets);
+}
 EXPORT_SYMBOL(__might_resched);
 
 void __cant_sleep(const char *file, int line, int preempt_offset)
diff --git a/rust/helpers/kernel.c b/rust/helpers/kernel.c
index da847059260b..9dff28f4618e 100644
--- a/rust/helpers/kernel.c
+++ b/rust/helpers/kernel.c
@@ -7,7 +7,7 @@ void rust_helper_cpu_relax(void)
 	cpu_relax();
 }
 
-void rust_helper___might_sleep(const char *file, int line)
+void rust_helper___might_sleep_precision(const char *file, int len, int line)
 {
-	__might_sleep(file, line);
+	__might_sleep_precision(file, len, line);
 }
diff --git a/rust/kernel/io/poll.rs b/rust/kernel/io/poll.rs
index a8caa08f86f2..d7e5be162b6e 100644
--- a/rust/kernel/io/poll.rs
+++ b/rust/kernel/io/poll.rs
@@ -10,10 +10,25 @@
     time::{delay::fsleep, Delta, Instant},
 };
 
+use core::panic::Location;
+
 /// Polls periodically until a condition is met or a timeout is reached.
 ///
 /// Public but hidden since it should only be used from public macros.
-#[doc(hidden)]
+///
+/// ```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), Delta::from_micros(42));
+/// drop(g);
+///
+/// # Ok::<(), Error>(())
+/// ```
+#[track_caller]
 pub fn read_poll_timeout<Op, Cond, T: Copy>(
     mut op: Op,
     cond: Cond,
@@ -28,6 +43,8 @@ pub fn read_poll_timeout<Op, Cond, T: Copy>(
     let sleep = !sleep_delta.is_zero();
     let timeout = !timeout_delta.is_zero();
 
+    might_sleep(Location::caller());
+
     let val = loop {
         let val = op()?;
         if cond(val) {
@@ -55,41 +72,13 @@ pub fn read_poll_timeout<Op, Cond, T: Copy>(
     }
 }
 
-/// Print debug information if it's called inside atomic sections.
-///
-/// Equivalent to the kernel's [`__might_sleep`].
-#[macro_export]
-macro_rules! __might_sleep {
-    () => {
-        #[cfg(CONFIG_DEBUG_ATOMIC_SLEEP)]
-        // SAFETY: FFI call.
-        unsafe {
-            $crate::bindings::__might_sleep(
-                c_str!(::core::file!()).as_char_ptr(),
-                ::core::line!() as i32,
-            )
-        }
-    };
-}
-
-/// Polls periodically until a condition is met or a timeout is reached.
-///
-/// `op` is called repeatedly until `cond` returns `true` or the timeout is
-///  reached. The return value of `op` is passed to `cond`.
-///
-/// `sleep_delta` is the duration to sleep between calls to `op`.
-/// If `sleep_delta` is less than one microsecond, the function will busy-wait.
-///
-/// `timeout_delta` is the maximum time to wait for `cond` to return `true`.
-///
-/// This macro can only be used in a nonatomic context.
-#[macro_export]
-macro_rules! readx_poll_timeout {
-    ($op:expr, $cond:expr, $sleep_delta:expr, $timeout_delta:expr) => {{
-        if !$sleep_delta.is_zero() {
-            $crate::__might_sleep!();
-        }
-
-        $crate::io::poll::read_poll_timeout($op, $cond, $sleep_delta, $timeout_delta)
-    }};
+fn might_sleep(loc: &Location<'_>) {
+    // SAFETY: FFI call.
+    unsafe {
+        crate::bindings::__might_sleep_precision(
+            loc.file().as_ptr().cast(),
+            loc.file().len() as i32,
+            loc.line() as i32,
+        )
+    }
 }

On Wed, 6 Nov 2024 13:35:09 -0800
Boqun Feng <boqun.feng@gmail.com> wrote:

> On Fri, Nov 01, 2024 at 10:01:20AM +0900, FUJITA Tomonori wrote:
>> Add read_poll_timeout functions which poll periodically until a
>> condition is met or a timeout is reached.
>> 
>> 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.
>> 
>> Unlike the C version, __might_sleep() is used instead of might_sleep()
>> to show proper debug info; the file name and line
>> number. might_resched() could be added to match what the C version
>> does but this function works without it.
>> 
>> The sleep_before_read argument isn't supported since there is no user
>> for now. It's rarely used in the C version.
>> 
>> For the proper debug info, readx_poll_timeout() and __might_sleep()
>> are implemented as a macro. We could implement them as a normal
>> function if there is a clean way to get a null-terminated string
>> without allocation from core::panic::Location::file().
>> 
> 
> So printk() actually support printing a string with a precison value,
> that is: a format string "%.*s" would take two inputs, one for the length
> and the other for the pointer to the string, for example you can do:
> 
> 	char *msg = "hello";
> 
> 	printk("%.*s\n", 5, msg);
> 
> This is similar to printf() in glibc [1].
> 
> If we add another __might_sleep_precision() which accepts a file name
> length:
> 
> 	void __might_sleep_precision(const char *file, int len, int line)
> 
> then we don't need to use macro here, I've attached a diff based
> on your whole patchset, and it seems working.

Ah, I didn't know this.

> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index be2e8c0a187e..b405b0d19bac 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -87,6 +87,8 @@ extern int dynamic_might_resched(void);
>  #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
>  extern void __might_resched(const char *file, int line, unsigned int offsets);
>  extern void __might_sleep(const char *file, int line);
> +extern void __might_resched_precision(const char *file, int len, int line, unsigned int offsets);
> +extern void __might_sleep_precision(const char *file, int len, int line);
>  extern void __cant_sleep(const char *file, int line, int preempt_offset);
>  extern void __cant_migrate(const char *file, int line);
>  
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 43e453ab7e20..f872aa18eaf0 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -8543,7 +8543,7 @@ void __init sched_init(void)
>  
>  #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
>  
> -void __might_sleep(const char *file, int line)
> +void __might_sleep_precision(const char *file, int len, int line)
>  {
>  	unsigned int state = get_current_state();
>  	/*
> @@ -8557,7 +8557,14 @@ void __might_sleep(const char *file, int line)
>  			(void *)current->task_state_change,
>  			(void *)current->task_state_change);
>  
> -	__might_resched(file, line, 0);
> +	__might_resched_precision(file, len, line, 0);
> +}
> +
> +void __might_sleep(const char *file, int line)
> +{
> +	long len = strlen(file);
> +
> +	__might_sleep_precision(file, len, line);
>  }
>  EXPORT_SYMBOL(__might_sleep);
>  
> @@ -8582,7 +8589,7 @@ static inline bool resched_offsets_ok(unsigned int offsets)
>  	return nested == offsets;
>  }
>  
> -void __might_resched(const char *file, int line, unsigned int offsets)
> +void __might_resched_precision(const char *file, int len, int line, unsigned int offsets)
>  {
>  	/* Ratelimiting timestamp: */
>  	static unsigned long prev_jiffy;
> @@ -8605,8 +8612,8 @@ void __might_resched(const char *file, int line, unsigned int offsets)
>  	/* Save this before calling printk(), since that will clobber it: */
>  	preempt_disable_ip = get_preempt_disable_ip(current);
>  
> -	pr_err("BUG: sleeping function called from invalid context at %s:%d\n",
> -	       file, line);
> +	pr_err("BUG: sleeping function called from invalid context at %.*s:%d\n",
> +	       len, file, line);
>  	pr_err("in_atomic(): %d, irqs_disabled(): %d, non_block: %d, pid: %d, name: %s\n",
>  	       in_atomic(), irqs_disabled(), current->non_block_count,
>  	       current->pid, current->comm);
> @@ -8631,6 +8638,13 @@ void __might_resched(const char *file, int line, unsigned int offsets)
>  	dump_stack();
>  	add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
>  }
> +
> +void __might_resched(const char *file, int line, unsigned int offsets)
> +{
> +	long len = strlen(file);
> +
> +	__might_resched_precision(file, len, line, offsets);
> +}
>  EXPORT_SYMBOL(__might_resched);
>  
>  void __cant_sleep(const char *file, int line, int preempt_offset)

Cc scheduler people to ask if they would accept the above change for
Rust or prefer that Rust itself handles the null-terminated string
issue.

On Wed 2024-11-06 13:35:09, Boqun Feng wrote:
> On Fri, Nov 01, 2024 at 10:01:20AM +0900, FUJITA Tomonori wrote:
> > Add read_poll_timeout functions which poll periodically until a
> > condition is met or a timeout is reached.
> > 
> > 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.
> > 
> > Unlike the C version, __might_sleep() is used instead of might_sleep()
> > to show proper debug info; the file name and line
> > number. might_resched() could be added to match what the C version
> > does but this function works without it.
> > 
> > The sleep_before_read argument isn't supported since there is no user
> > for now. It's rarely used in the C version.
> > 
> > For the proper debug info, readx_poll_timeout() and __might_sleep()
> > are implemented as a macro. We could implement them as a normal
> > function if there is a clean way to get a null-terminated string
> > without allocation from core::panic::Location::file().
> > 
> 
> So printk() actually support printing a string with a precison value,
> that is: a format string "%.*s" would take two inputs, one for the length
> and the other for the pointer to the string, for example you can do:
> 
> 	char *msg = "hello";
> 
> 	printk("%.*s\n", 5, msg);
> 
> This is similar to printf() in glibc [1].
> 
> If we add another __might_sleep_precision() which accepts a file name
> length:
> 
> 	void __might_sleep_precision(const char *file, int len, int line)
> 
> then we don't need to use macro here, I've attached a diff based
> on your whole patchset, and it seems working.
> 
> Cc printk folks to if they know any limitation on using precision.

I am not aware of any printk() limitation here. The "%.*s" format
should work the same way as in printf() in the userspace.

Best Regards,
Petr

On Fri, Nov 01, 2024 at 10:01:20AM +0900, FUJITA Tomonori wrote:
[...]
> @@ -44,6 +45,7 @@
>  pub mod page;
>  pub mod prelude;
>  pub mod print;
> +pub mod processor;
>  pub mod sizes;
>  pub mod rbtree;
>  mod static_assert;
> diff --git a/rust/kernel/processor.rs b/rust/kernel/processor.rs
> new file mode 100644
> index 000000000000..eeeff4be84fa
> --- /dev/null
> +++ b/rust/kernel/processor.rs

What else would we put into this file? `smp_processor_id()` and IPI
functionality? If so, I would probably want to rename this to cpu.rs.

Regards,
Boqun

> @@ -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() }
> +}
> -- 
> 2.43.0
> 
>

On Wed, 6 Nov 2024 10:18:03 -0800
Boqun Feng <boqun.feng@gmail.com> wrote:

> On Fri, Nov 01, 2024 at 10:01:20AM +0900, FUJITA Tomonori wrote:
> [...]
>> @@ -44,6 +45,7 @@
>>  pub mod page;
>>  pub mod prelude;
>>  pub mod print;
>> +pub mod processor;
>>  pub mod sizes;
>>  pub mod rbtree;
>>  mod static_assert;
>> diff --git a/rust/kernel/processor.rs b/rust/kernel/processor.rs
>> new file mode 100644
>> index 000000000000..eeeff4be84fa
>> --- /dev/null
>> +++ b/rust/kernel/processor.rs
> 
> What else would we put into this file? `smp_processor_id()` and IPI
> functionality?

Yeah, we would need smp_processor_id() but not sure about the other
functions. There aren't many processor-related functions that Rust
drivers directly need to call, I guess.

> If so, I would probably want to rename this to cpu.rs.

Fine by me, I'll go with cpu.rs in the next version.

I chose processor.rs just because the C side uses processor.h for
cpu_relax() but cpu.rs also looks good.