linux-kernel - [PATCH] rust: i2c: prepare for `core::ffi::CStr`

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Message-ID: <20251123163536.1771801-1-ojeda@kernel.org>
Date: Sun, 23 Nov 2025 17:35:36 +0100
From: Miguel Ojeda <ojeda@...nel.org>
To: Igor Korotin <igor.korotin.linux@...il.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Greg KH <greg@...ah.com>,
	Danilo Krummrich <dakr@...nel.org>,
	Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>
Cc: Daniel Almeida <daniel.almeida@...labora.com>,
	rust-for-linux@...r.kernel.org,
	Boqun Feng <boqun.feng@...il.com>,
	Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <lossin@...nel.org>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>,
	Trevor Gross <tmgross@...ch.edu>,
	linux-kernel@...r.kernel.org,
	patches@...ts.linux.dev
Subject: [PATCH] rust: i2c: prepare for `core::ffi::CStr`

The rust-next tree contains commit:

    3b83f5d5e78a ("rust: replace `CStr` with `core::ffi::CStr`")

which, when merged together with commits:

    57c5bd9aee94 ("rust: i2c: add basic I2C device and driver abstractions")
    f3cc26a417b7 ("rust: i2c: add manual I2C device creation abstractions")

from this tree (driver-core), produces errors like the following:

    error[E0599]: no method named `len_with_nul` found for reference `&'static ffi::CStr` in the current scope
      --> rust/kernel/i2c.rs:48:16
       |
    48 |             id.len_with_nul() <= Self::I2C_NAME_SIZE,
       |                ^^^^^^^^^^^^ method not found in `&CStr`

    error[E0599]: no method named `as_bytes_with_nul` found for reference `&'static ffi::CStr` in the current scope
      --> rust/kernel/i2c.rs:51:22
       |
    51 |         let src = id.as_bytes_with_nul();
       |                      ^^^^^^^^^^^^^^^^^
       |
    help: there is a method `to_bytes_with_nul` with a similar name
       |
    51 |         let src = id.to_bytes_with_nul();
       |                      ~~~~~~~~~~~~~~~~~

which were detected in linux-next by Stephen [1].

The `i2c` code can be independently prepared to be ready for the change,
thus do so.

The change is similar to the one done by Tamir in commit 657403637f7d
("rust: acpi: use `core::ffi::CStr` method names").

Link: https://lore.kernel.org/all/20251120181111.65ce75a0@canb.auug.org.au/ [1]
Signed-off-by: Miguel Ojeda <ojeda@...nel.org>
---
I see that Stephen added this in his Friday's resolution. However, the
`CStrExt` import does not seem needed as it also comes from the prelude,
so that may be removed.

 rust/kernel/i2c.rs | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/rust/kernel/i2c.rs b/rust/kernel/i2c.rs
index 95b056cc1a71..491e6cc25cf4 100644
--- a/rust/kernel/i2c.rs
+++ b/rust/kernel/i2c.rs
@@ -44,11 +44,8 @@ impl DeviceId {
     /// Create a new device id from an I2C 'id' string.
     #[inline(always)]
     pub const fn new(id: &'static CStr) -> Self {
-        build_assert!(
-            id.len_with_nul() <= Self::I2C_NAME_SIZE,
-            "ID exceeds 20 bytes"
-        );
-        let src = id.as_bytes_with_nul();
+        let src = id.to_bytes_with_nul();
+        build_assert!(src.len() <= Self::I2C_NAME_SIZE, "ID exceeds 20 bytes");
         let mut i2c: bindings::i2c_device_id = pin_init::zeroed();
         let mut i = 0;
         while i < src.len() {
@@ -434,11 +431,8 @@ impl I2cBoardInfo {
     /// Create a new [`I2cBoardInfo`] for a kernel driver.
     #[inline(always)]
     pub const fn new(type_: &'static CStr, addr: u16) -> Self {
-        build_assert!(
-            type_.len_with_nul() <= Self::I2C_TYPE_SIZE,
-            "Type exceeds 20 bytes"
-        );
-        let src = type_.as_bytes_with_nul();
+        let src = type_.to_bytes_with_nul();
+        build_assert!(src.len() <= Self::I2C_TYPE_SIZE, "Type exceeds 20 bytes");
         let mut i2c_board_info: bindings::i2c_board_info = pin_init::zeroed();
         let mut i: usize = 0;
         while i < src.len() {

base-commit: 4635406417bb842862d6322c461743c9b128c444
--
2.52.0