[v4] Add Rust version of might_sleep()

[PATCH v4 1/2] rust: Introduce file_from_location()

Posted by Boqun Feng 3 months, 3 weeks ago

Most of kernel debugging facilities take a nul-terminated string for
file names for a callsite (generated from __FILE__), however the Rust
courterpart, Location, would return a Rust string (not nul-terminated)
from method .file(). And such a string cannot be passed to C debugging
function directly.

There is ongoing work to support a Location::file_with_nul() [1], which
returns a nul-terminated string from a Location. Since it's still
working in progress, and it will take some time before the feature
finally gets stabilized and the kernel's minimal rustc version might
also take a while to bump to a version that at least has that feature,
introduce a file_from_location() function, which returns a warning
string if Location::file_with_nul() is not available.

This should work in most cases because as for now the known usage of
Location::file_with_nul() is only in debugging code (e.g. might_sleep())
and there might be other information reported by the debugging code that
could help locate the problematic function, so missing the file name is
fine at the moment.

Link: https://github.com/rust-lang/rust/issues/141727 [1]
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 init/Kconfig       |  3 +++
 rust/kernel/lib.rs | 43 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+)

diff --git a/init/Kconfig b/init/Kconfig
index af4c2f085455..6f4ec5633ffa 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -142,6 +142,9 @@ config RUSTC_HAS_SPAN_FILE
 config RUSTC_HAS_UNNECESSARY_TRANSMUTES
 	def_bool RUSTC_VERSION >= 108800
 
+config RUSTC_HAS_FILE_WITH_NUL
+	def_bool RUSTC_VERSION >= 108900
+
 config PAHOLE_VERSION
 	int
 	default $(shell,$(srctree)/scripts/pahole-version.sh $(PAHOLE))
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 6b4774b2b1c3..57cff1ca8b90 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -40,6 +40,10 @@
 #![cfg_attr(not(CONFIG_RUSTC_HAS_COERCE_POINTEE), feature(coerce_unsized))]
 #![cfg_attr(not(CONFIG_RUSTC_HAS_COERCE_POINTEE), feature(dispatch_from_dyn))]
 #![cfg_attr(not(CONFIG_RUSTC_HAS_COERCE_POINTEE), feature(unsize))]
+//
+// `feature(file_with_nul)` is expected to become stable. Before Rust 1.89.0, it did not exist, so
+// enable it conditionally.
+#![cfg_attr(CONFIG_RUSTC_HAS_FILE_WITH_NUL, feature(file_with_nul))]
 
 // Ensure conditional compilation based on the kernel configuration works;
 // otherwise we may silently break things like initcall handling.
@@ -274,3 +278,42 @@ macro_rules! asm {
         ::core::arch::asm!( $($asm)*, $($rest)* )
     };
 }
+
+/// Gets the C string file name of a [`Location`].
+///
+/// If `file_with_nul()` is not available, returns a string that warns about it.
+///
+/// [`Location`]: core::panic::Location
+///
+/// # Examples
+///
+/// ```
+/// # use kernel::file_from_location;
+///
+/// #[track_caller]
+/// fn foo() {
+///     let caller = core::panic::Location::caller();
+///
+///     // Output:
+///     // - A path like "rust/kernel/example.rs" if file_with_nul() available.
+///     // - "<Location::file_with_nul() not supported>" otherwise.
+///     let caller_file = file_from_location(caller);
+///
+///     // Prints out the message with caller's file name.
+///     pr_info!("foo() called in file {caller_file:?}\n");
+///
+///     # if cfg!(CONFIG_RUSTC_HAS_FILE_WITH_NUL) {
+///     #     assert_eq!(Ok(caller.file()), caller_file.to_str());
+///     # }
+/// }
+///
+/// # foo();
+/// ```
+#[inline]
+pub fn file_from_location<'a>(_loc: &'a core::panic::Location<'a>) -> &'a core::ffi::CStr {
+    #[cfg(CONFIG_RUSTC_HAS_FILE_WITH_NUL)]
+    { _loc.file_with_nul() }
+
+    #[cfg(not(CONFIG_RUSTC_HAS_FILE_WITH_NUL))]
+    { c"<Location::file_with_nul() not supported>" }
+}
-- 
2.39.5 (Apple Git-154)

Re: [PATCH v4 1/2] rust: Introduce file_from_location()

Posted by Miguel Ojeda 3 months, 3 weeks ago

On Thu, Jun 19, 2025 at 5:10 PM Boqun Feng <boqun.feng@gmail.com> wrote:
>
> +///     // - A path like "rust/kernel/example.rs" if file_with_nul() available.

"is available."

> +pub fn file_from_location<'a>(_loc: &'a core::panic::Location<'a>) -> &'a core::ffi::CStr {
> +    #[cfg(CONFIG_RUSTC_HAS_FILE_WITH_NUL)]
> +    { _loc.file_with_nul() }
> +
> +    #[cfg(not(CONFIG_RUSTC_HAS_FILE_WITH_NUL))]
> +    { c"<Location::file_with_nul() not supported>" }
> +}

If a `let _` works, then it may be better -- please see a similar case at:

    https://lore.kernel.org/rust-for-linux/CANiq72=ph_XG0TtkdsNJCUZMiAMYBo11eJaCTLCTpTAFXtcNMA@mail.gmail.com/

The new version looks great, thanks!

Cheers,
Miguel

Re: [PATCH v4 1/2] rust: Introduce file_from_location()

Posted by Boqun Feng 3 months, 3 weeks ago

On Thu, Jun 19, 2025 at 10:42:44PM +0200, Miguel Ojeda wrote:
> On Thu, Jun 19, 2025 at 5:10 PM Boqun Feng <boqun.feng@gmail.com> wrote:
> >
> > +///     // - A path like "rust/kernel/example.rs" if file_with_nul() available.
> 
> "is available."
> 

Fixed.

> > +pub fn file_from_location<'a>(_loc: &'a core::panic::Location<'a>) -> &'a core::ffi::CStr {
> > +    #[cfg(CONFIG_RUSTC_HAS_FILE_WITH_NUL)]
> > +    { _loc.file_with_nul() }
> > +
> > +    #[cfg(not(CONFIG_RUSTC_HAS_FILE_WITH_NUL))]
> > +    { c"<Location::file_with_nul() not supported>" }
> > +}
> 
> If a `let _` works, then it may be better -- please see a similar case at:
> 
>     https://lore.kernel.org/rust-for-linux/CANiq72=ph_XG0TtkdsNJCUZMiAMYBo11eJaCTLCTpTAFXtcNMA@mail.gmail.com/
> 

Make sense, applied.

> The new version looks great, thanks!
> 

Thanks! I pushed the updated version at:

	https://git.kernel.org/pub/scm/linux/kernel/git/boqun/linux.git/log/?h=rust-sched-v2

"-v2" because it's going to be a v2 of the pull request.

Regards,
Boqun

> Cheers,
> Miguel

[tip: sched/core] rust: Introduce file_from_location()

Posted by tip-bot2 for Boqun Feng 3 months, 1 week ago

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     0aa2b78ce5a9eac8f3332192ea77755d63a831cd
Gitweb:        https://git.kernel.org/tip/0aa2b78ce5a9eac8f3332192ea77755d63a831cd
Author:        Boqun Feng <boqun.feng@gmail.com>
AuthorDate:    Sun, 15 Jun 2025 15:14:00 -07:00
Committer:     Boqun Feng <boqun.feng@gmail.com>
CommitterDate: Tue, 24 Jun 2025 15:53:46 -07:00

rust: Introduce file_from_location()

Most of kernel debugging facilities take a nul-terminated string for
file names for a callsite (generated from __FILE__), however the Rust
courterpart, Location, would return a Rust string (not nul-terminated)
from method .file(). And such a string cannot be passed to C debugging
function directly.

There is ongoing work to support a Location::file_with_nul() [1], which
returns a nul-terminated string from a Location. Since it's still
working in progress, and it will take some time before the feature
finally gets stabilized and the kernel's minimal rustc version might
also take a while to bump to a version that at least has that feature,
introduce a file_from_location() function, which returns a warning
string if Location::file_with_nul() is not available.

This should work in most cases because as for now the known usage of
Location::file_with_nul() is only in debugging code (e.g. might_sleep())
and there might be other information reported by the debugging code that
could help locate the problematic function, so missing the file name is
fine at the moment.

Link: https://github.com/rust-lang/rust/issues/141727 [1]
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/r/20250619151007.61767-2-boqun.feng@gmail.com
---
 init/Kconfig       |  3 +++-
 rust/kernel/lib.rs | 48 +++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 51 insertions(+)

diff --git a/init/Kconfig b/init/Kconfig
index af4c2f0..6f4ec56 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -142,6 +142,9 @@ config RUSTC_HAS_SPAN_FILE
 config RUSTC_HAS_UNNECESSARY_TRANSMUTES
 	def_bool RUSTC_VERSION >= 108800
 
+config RUSTC_HAS_FILE_WITH_NUL
+	def_bool RUSTC_VERSION >= 108900
+
 config PAHOLE_VERSION
 	int
 	default $(shell,$(srctree)/scripts/pahole-version.sh $(PAHOLE))
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 6b4774b..717a5b6 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -40,6 +40,10 @@
 #![cfg_attr(not(CONFIG_RUSTC_HAS_COERCE_POINTEE), feature(coerce_unsized))]
 #![cfg_attr(not(CONFIG_RUSTC_HAS_COERCE_POINTEE), feature(dispatch_from_dyn))]
 #![cfg_attr(not(CONFIG_RUSTC_HAS_COERCE_POINTEE), feature(unsize))]
+//
+// `feature(file_with_nul)` is expected to become stable. Before Rust 1.89.0, it did not exist, so
+// enable it conditionally.
+#![cfg_attr(CONFIG_RUSTC_HAS_FILE_WITH_NUL, feature(file_with_nul))]
 
 // Ensure conditional compilation based on the kernel configuration works;
 // otherwise we may silently break things like initcall handling.
@@ -274,3 +278,47 @@ macro_rules! asm {
         ::core::arch::asm!( $($asm)*, $($rest)* )
     };
 }
+
+/// Gets the C string file name of a [`Location`].
+///
+/// If `file_with_nul()` is not available, returns a string that warns about it.
+///
+/// [`Location`]: core::panic::Location
+///
+/// # Examples
+///
+/// ```
+/// # use kernel::file_from_location;
+///
+/// #[track_caller]
+/// fn foo() {
+///     let caller = core::panic::Location::caller();
+///
+///     // Output:
+///     // - A path like "rust/kernel/example.rs" if file_with_nul() is available.
+///     // - "<Location::file_with_nul() not supported>" otherwise.
+///     let caller_file = file_from_location(caller);
+///
+///     // Prints out the message with caller's file name.
+///     pr_info!("foo() called in file {caller_file:?}\n");
+///
+///     # if cfg!(CONFIG_RUSTC_HAS_FILE_WITH_NUL) {
+///     #     assert_eq!(Ok(caller.file()), caller_file.to_str());
+///     # }
+/// }
+///
+/// # foo();
+/// ```
+#[inline]
+pub fn file_from_location<'a>(loc: &'a core::panic::Location<'a>) -> &'a core::ffi::CStr {
+    #[cfg(CONFIG_RUSTC_HAS_FILE_WITH_NUL)]
+    {
+        loc.file_with_nul()
+    }
+
+    #[cfg(not(CONFIG_RUSTC_HAS_FILE_WITH_NUL))]
+    {
+        let _ = loc;
+        c"<Location::file_with_nul() not supported>"
+    }
+}