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

[Tamir Duberstein <tamird@kernel.org>]

On Mon, Mar 2, 2026 at 12:31 PM Gary Guo <gary@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 <gregkh@linuxfoundation.org>
> > Reviewed-by: Alice Ryhl <aliceryhl@google.com>
> > Signed-off-by: Tamir Duberstein <tamird@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.

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

Done in v2.

>
> Best,
> Gary

Thanks for having a look!
Tamir