[PATCH RFC 3/3] rust: percpu: add a rust per-CPU variable test

[Mitchell Levy <levymitchell0@gmail.com>]

Add a short exercise for Rust's per-CPU variable API, modelled after
lib/percpu_test.c

Signed-off-by: Mitchell Levy <levymitchell0@gmail.com>
---
 lib/Kconfig.debug       |  9 +++++++
 lib/Makefile            |  1 +
 lib/percpu_test_rust.rs | 65 +++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 75 insertions(+)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index f3d723705879..75a91f1766ce 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -2404,6 +2404,15 @@ config PERCPU_TEST
 
 	  If unsure, say N.
 
+config PERCPU_TEST_RUST
+	tristate "Rust per cpu operations test"
+	depends on m && DEBUG_KERNEL && RUST
+	help
+	  Enable this option to build a test module which validates Rust per-cpu
+	  operations.
+
+	  If unsure, say N.
+
 config ATOMIC64_SELFTEST
 	tristate "Perform an atomic64_t self-test"
 	help
diff --git a/lib/Makefile b/lib/Makefile
index a8155c972f02..0ea8d414763c 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -301,6 +301,7 @@ obj-$(CONFIG_RBTREE_TEST) += rbtree_test.o
 obj-$(CONFIG_INTERVAL_TREE_TEST) += interval_tree_test.o
 
 obj-$(CONFIG_PERCPU_TEST) += percpu_test.o
+obj-$(CONFIG_PERCPU_TEST_RUST) += percpu_test_rust.o
 
 obj-$(CONFIG_ASN1) += asn1_decoder.o
 obj-$(CONFIG_ASN1_ENCODER) += asn1_encoder.o
diff --git a/lib/percpu_test_rust.rs b/lib/percpu_test_rust.rs
new file mode 100644
index 000000000000..60df44332d7a
--- /dev/null
+++ b/lib/percpu_test_rust.rs
@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: GPL-2.0
+//! A simple self test for the rust per-CPU API.
+use kernel::{
+    define_per_cpu, percpu::cpu_guard::*, percpu::*, pr_info, prelude::*, unsafe_get_per_cpu_ref,
+};
+
+module! {
+    type: PerCpuTestModule,
+    name: "percpu_test_rust",
+    author: "Mitchell Levy",
+    description: "Test code to exercise the Rust Per CPU variable API",
+    license: "GPL v2",
+}
+
+struct PerCpuTestModule;
+
+define_per_cpu!(PERCPU: i64 = 0);
+define_per_cpu!(UPERCPU: u64 = 0);
+
+impl kernel::Module for PerCpuTestModule {
+    fn init(_module: &'static ThisModule) -> Result<Self, Error> {
+        pr_info!("rust percpu test start\n");
+
+        let mut native: i64 = 0;
+        let mut pcpu: PerCpuRef<i64> = unsafe { unsafe_get_per_cpu_ref!(PERCPU, CpuGuard::new()) };
+
+        native += -1;
+        *pcpu += -1;
+        assert!(native == *pcpu && native == -1);
+
+        native += 1;
+        *pcpu += 1;
+        assert!(native == *pcpu && native == 0);
+
+        let mut unative: u64 = 0;
+        let mut upcpu: PerCpuRef<u64> =
+            unsafe { unsafe_get_per_cpu_ref!(UPERCPU, CpuGuard::new()) };
+
+        unative += 1;
+        *upcpu += 1;
+        assert!(unative == *upcpu && unative == 1);
+
+        unative = unative.wrapping_add((-1i64) as u64);
+        *upcpu = upcpu.wrapping_add((-1i64) as u64);
+        assert!(unative == *upcpu && unative == 0);
+
+        unative = unative.wrapping_add((-1i64) as u64);
+        *upcpu = upcpu.wrapping_add((-1i64) as u64);
+        assert!(unative == *upcpu && unative == (-1i64) as u64);
+
+        unative = 0;
+        *upcpu = 0;
+
+        unative = unative.wrapping_sub(1);
+        *upcpu = upcpu.wrapping_sub(1);
+        assert!(unative == *upcpu && unative == (-1i64) as u64);
+        assert!(unative == *upcpu && unative == u64::MAX);
+
+        pr_info!("rust percpu test done\n");
+
+        // Return Err to unload the module
+        Result::Err(EINVAL)
+    }
+}
+

-- 
2.34.1