[PATCH 3/7] rust: crc_ccitt: add CRC-CCITT abstraction

[Ayush Singh]

The module is gated behind the new RUST_CRC_CCITT_ABSTRACTIONS Kconfig
symbol, which selects CRC_CCITT, so the C library is only built when a
Rust user actually needs it.

Signed-off-by: Ayush Singh <ayush@xxxxxxxxxxxxxxx>
---
 MAINTAINERS                     |  1 +
 lib/crc/Kconfig                 |  7 +++++++
 rust/bindings/bindings_helper.h |  1 +
 rust/kernel/crc_ccitt.rs        | 26 ++++++++++++++++++++++++++
 rust/kernel/lib.rs              |  2 ++
 5 files changed, 37 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 6008f16ae2ca..1e3b42eff741 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -6921,6 +6921,7 @@ T:	git https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux.git crc-ne
 F:	Documentation/staging/crc*
 F:	include/linux/crc*
 F:	lib/crc/
+F:	rust/kernel/crc*
 F:	scripts/gen-crc-consts.py
 
 CREATIVE SB0540
diff --git a/lib/crc/Kconfig b/lib/crc/Kconfig
index 927fc6a6b2b9..aceb8fe8f0ed 100644
--- a/lib/crc/Kconfig
+++ b/lib/crc/Kconfig
@@ -32,6 +32,13 @@ config CRC_CCITT
 	  The CRC-CCITT library functions.  Select this if your module uses any
 	  of the functions from <linux/crc-ccitt.h>.
 
+config RUST_CRC_CCITT_ABSTRACTIONS
+	bool "Rust CRC-CCITT abstractions"
+	depends on RUST
+	select CRC_CCITT
+	help
+	  This enables the Rust abstraction for the CRC-CCITT API.
+
 config CRC_ITU_T
 	tristate
 	help
diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index 24d659a87c1d..6eb3caaee497 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -49,6 +49,7 @@
 #include <linux/cpu.h>
 #include <linux/cpufreq.h>
 #include <linux/cpumask.h>
+#include <linux/crc-ccitt.h>
 #include <linux/cred.h>
 #include <linux/debugfs.h>
 #include <linux/device/faux.h>
diff --git a/rust/kernel/crc_ccitt.rs b/rust/kernel/crc_ccitt.rs
new file mode 100644
index 000000000000..6042ada16967
--- /dev/null
+++ b/rust/kernel/crc_ccitt.rs
@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! CRC-CCITT computation.
+//!
+//! C header: [`include/linux/crc-ccitt.h`](srctree/include/linux/crc-ccitt.h)
+
+/// Computes the CRC-CCITT of `data`, starting from the seed value `crc`.
+///
+/// Pass the result back in as `crc` to compute the checksum of a buffer
+/// incrementally.
+///
+/// # Examples
+///
+/// ```
+/// use kernel::crc_ccitt::crc_ccitt;
+///
+/// let one_shot = crc_ccitt(0xffff, b"hello world");
+/// let split = crc_ccitt(crc_ccitt(0xffff, b"hello "), b"world");
+/// assert_eq!(one_shot, split);
+/// ```
+#[inline]
+pub fn crc_ccitt(crc: u16, data: &[u8]) -> u16 {
+    // SAFETY: `data.as_ptr()` is valid for reads of `data.len()` bytes for the
+    // duration of the call, since it is derived from a live shared slice.
+    unsafe { bindings::crc_ccitt(crc, data.as_ptr(), data.len()) }
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 3edc343caba5..45c4f4db51d2 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -61,6 +61,8 @@
 #[cfg(CONFIG_CPU_FREQ)]
 pub mod cpufreq;
 pub mod cpumask;
+#[cfg(CONFIG_RUST_CRC_CCITT_ABSTRACTIONS)]
+pub mod crc_ccitt;
 pub mod cred;
 pub mod debugfs;
 pub mod device;

-- 
2.55.0