[PATCH] rust: rename `kernel::c_str!` to `str_to_cstr!`

[Tamir Duberstein]

Now that all literals are C-Strings, rename and update the documentation
of this macro to clarify its intended purpose.

Link: https://github.com/Rust-for-Linux/linux/issues/1075
Acked-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
Reviewed-by: Alice Ryhl <alic...@google.com>
Signed-off-by: Tamir Duberstein <tam...@kernel.org>
---
This patch completes the work of replacing our custom `CStr` with
upstream's.
---
rust/kernel/bug.rs | 2 +-
rust/kernel/configfs.rs | 2 +-
rust/kernel/drm/ioctl.rs | 2 +-
rust/kernel/kunit.rs | 3 ++-
rust/kernel/str.rs | 19 ++++++++++++++-----
rust/kernel/sync.rs | 4 ++--
rust/kernel/sync/lock/global.rs | 3 ++-
rust/kernel/workqueue.rs | 6 +++---
8 files changed, 26 insertions(+), 15 deletions(-)

diff --git a/rust/kernel/bug.rs b/rust/kernel/bug.rs
index ed943960f851..f7cb673b1766 100644
--- a/rust/kernel/bug.rs
+++ b/rust/kernel/bug.rs
@@ -80,7 +80,7 @@ macro_rules! warn_flags {
// with a valid null-terminated string.
unsafe {
$crate::bindings::warn_slowpath_fmt(
- $crate::c_str!(::core::file!()).as_char_ptr(),
+ $crate::str_to_cstr!(::core::file!()).as_char_ptr(),
line!() as $crate::ffi::c_int,
$flags as $crate::ffi::c_uint,
::core::ptr::null(),
diff --git a/rust/kernel/configfs.rs b/rust/kernel/configfs.rs
index 2339c6467325..930f17bb2041 100644
--- a/rust/kernel/configfs.rs
+++ b/rust/kernel/configfs.rs
@@ -1000,7 +1000,7 @@ macro_rules! configfs_attrs {
$crate::configfs::Attribute<$attr, $data, $data> =
unsafe {
$crate::configfs::Attribute::new(
- $crate::c_str!(::core::stringify!($name)),
+ $crate::str_to_cstr!(::core::stringify!($name)),
)
};
)*
diff --git a/rust/kernel/drm/ioctl.rs b/rust/kernel/drm/ioctl.rs
index cf328101dde4..6a87f489dc88 100644
--- a/rust/kernel/drm/ioctl.rs
+++ b/rust/kernel/drm/ioctl.rs
@@ -157,7 +157,7 @@ macro_rules! declare_drm_ioctls {
},
flags: $flags,
name: $crate::str::as_char_ptr_in_const_context(
- $crate::c_str!(::core::stringify!($cmd)),
+ $crate::str_to_cstr!(::core::stringify!($cmd)),
),
}
),*];
diff --git a/rust/kernel/kunit.rs b/rust/kernel/kunit.rs
index f93f24a60bdd..5802a3507ecc 100644
--- a/rust/kernel/kunit.rs
+++ b/rust/kernel/kunit.rs
@@ -59,7 +59,8 @@ macro_rules! kunit_assert {

static FILE: &'static $crate::str::CStr = $file;
static LINE: i32 = ::core::line!() as i32 - $diff;
- static CONDITION: &'static $crate::str::CStr = $crate::c_str!(stringify!($condition));
+ static CONDITION: &'static $crate::str::CStr =
+ $crate::str_to_cstr!(stringify!($condition));

// SAFETY: FFI call without safety requirements.
let kunit_test = unsafe { $crate::bindings::kunit_get_current_test() };
diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
index fa87779d2253..8bb40de007d4 100644
--- a/rust/kernel/str.rs
+++ b/rust/kernel/str.rs
@@ -376,19 +376,28 @@ fn as_ref(&self) -> &BStr {
}
}

-/// Creates a new [`CStr`] from a string literal.
+/// Creates a new [`CStr`] at compile time.
///
-/// The string literal should not contain any `NUL` bytes.
+/// Rust supports C string literals since Rust 1.77, and they should be used instead of this macro
+/// where possible. This macro exists to allow static *non-literal* C strings to be created at
+/// compile time. This is most often used in other macros.
+///
+/// # Panics
+///
+/// This macro panics if the operand contains an interior `NUL` byte.
///
/// # Examples
///
/// ```
-/// # use kernel::c_str;
+/// # use kernel::str_to_cstr;
/// # use kernel::str::CStr;
-/// const MY_CSTR: &CStr = c_str!("My awesome CStr!");
+/// const MY_CSTR: &CStr = str_to_cstr!(concat!(file!(), ":", line!(), ": My CStr!"));
/// ```
#[macro_export]
-macro_rules! c_str {
+macro_rules! str_to_cstr {
+ // NB: we could write `($str:lit) => compile_error!("use a C string literal instead");` here but
+ // that would trigger when the literal is at the top of several macro expansions. That would be
+ // too limiting to macro authors, so we rely on the name as a hint instead.
($str:expr) => {{
const S: &str = concat!($str, "\0");
const C: &$crate::str::CStr = match $crate::str::CStr::from_bytes_with_nul(S.as_bytes()) {
diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
index 993dbf2caa0e..ecf02a67ec35 100644
--- a/rust/kernel/sync.rs
+++ b/rust/kernel/sync.rs
@@ -154,9 +154,9 @@ macro_rules! static_lock_class {
#[macro_export]
macro_rules! optional_name {
() => {
- $crate::c_str!(::core::concat!(::core::file!(), ":", ::core::line!()))
+ $crate::str_to_cstr!(::core::concat!(::core::file!(), ":", ::core::line!()))
};
($name:literal) => {
- $crate::c_str!($name)
+ $crate::str_to_cstr!($name)
};
}
diff --git a/rust/kernel/sync/lock/global.rs b/rust/kernel/sync/lock/global.rs
index aecbdc34738f..81f46229be7d 100644
--- a/rust/kernel/sync/lock/global.rs
+++ b/rust/kernel/sync/lock/global.rs
@@ -272,7 +272,8 @@ macro_rules! global_lock {
$pub enum $name {}

impl $crate::sync::lock::GlobalLockBackend for $name {
- const NAME: &'static $crate::str::CStr = $crate::c_str!(::core::stringify!($name));
+ const NAME: &'static $crate::str::CStr =
+ $crate::str_to_cstr!(::core::stringify!($name));
type Item = $valuety;
type Backend = $crate::global_lock_inner!(backend $kind);

diff --git a/rust/kernel/workqueue.rs b/rust/kernel/workqueue.rs
index 706e833e9702..7616d71df68e 100644
--- a/rust/kernel/workqueue.rs
+++ b/rust/kernel/workqueue.rs
@@ -212,7 +212,7 @@ macro_rules! new_delayed_work {
$crate::workqueue::DelayedWork::new(
$crate::optional_name!(),
$crate::static_lock_class!(),
- $crate::c_str!(::core::concat!(
+ $crate::str_to_cstr!(::core::concat!(
::core::file!(),
":",
::core::line!(),
@@ -223,9 +223,9 @@ macro_rules! new_delayed_work {
};
($name:literal) => {
$crate::workqueue::DelayedWork::new(
- $crate::c_str!($name),
+ $crate::str_to_cstr!($name),
$crate::static_lock_class!(),
- $crate::c_str!(::core::concat!($name, "_timer")),
+ $crate::str_to_cstr!(::core::concat!($name, "_timer")),
$crate::static_lock_class!(),
)
};

---
base-commit: 11439c4635edd669ae435eec308f4ab8a0804808
change-id: 20260302-cstr-rename-macro-64201be6c969

Best regards,
--
Tamir Duberstein <tam...@kernel.org>

[Gary Guo]

On Mon Mar 2, 2026 at 5:20 PM GMT, Tamir Duberstein wrote:
> Now that all literals are C-Strings, rename and update the documentation
> of this macro to clarify its intended purpose.
>
> Link: https://github.com/Rust-for-Linux/linux/issues/1075
> Acked-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
> Reviewed-by: Alice Ryhl <alic...@google.com>
> Signed-off-by: Tamir Duberstein <tam...@kernel.org>

Do we really need to perform the rename? I think updating the documentation
should be good enough?

If the only concern is misuse of the macro then perhaps I can just add a
lint for this in klint.

Perhaps keep a copy of the old example and add a comment saying this is allowed
but c"literal" should be preferred.

Best,
Gary

[Tamir Duberstein]

On Mon, Mar 2, 2026 at 12:31 PM Gary Guo <ga...@garyguo.net> wrote:
>
> On Mon Mar 2, 2026 at 5:20 PM GMT, Tamir Duberstein wrote:
> > Now that all literals are C-Strings, rename and update the documentation
> > of this macro to clarify its intended purpose.
> >
> > Link: https://github.com/Rust-for-Linux/linux/issues/1075
> > Acked-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
> > Reviewed-by: Alice Ryhl <alic...@google.com>
> > Signed-off-by: Tamir Duberstein <tam...@kernel.org>
>
> Do we really need to perform the rename? I think updating the documentation
> should be good enough?
>
> If the only concern is misuse of the macro then perhaps I can just add a
> lint for this in klint.

That would be better! I'll change v2 to only update the documentation.

Done in v2.

>
> Best,
> Gary

Thanks for having a look!
Tamir