[PATCH 3/8] samples: rust_minimal: demonstrate string module parameter

[Matthew Wood <thepacketgeek@gmail.com>]

Add a `test_str` string parameter alongside the existing integer
parameter (renamed from `test_parameter` to `test_int` for clarity)
in the rust_minimal sample module.

The init function now prints both parameters to the kernel log,
showing how string parameters are declared, defaulted, and read
back via StringParam::as_cstr().

Also add module-level documentation showing usage via insmod and
kernel command-line with dotted notation.

Signed-off-by: Matthew Wood <thepacketgeek@gmail.com>
---
 samples/rust/rust_minimal.rs | 31 ++++++++++++++++++++++++++++---
 1 file changed, 28 insertions(+), 3 deletions(-)

diff --git a/samples/rust/rust_minimal.rs b/samples/rust/rust_minimal.rs
index 8eb9583571d7..59955e95e31a 100644
--- a/samples/rust/rust_minimal.rs
+++ b/samples/rust/rust_minimal.rs
@@ -1,6 +1,23 @@
 // SPDX-License-Identifier: GPL-2.0
 
 //! Rust minimal sample.
+//!
+//! This is a sample module written in Rust. It is intended to be a minimal
+//! example of how to write a module in Rust. It does not do anything useful,
+//! except print a message when it is loaded and unloaded.
+//!
+//! It provides examples of how to receive module parameters, which can be provided
+//! by the user when the module is loaded:
+//!
+//! ```
+//! insmod /lib/modules/$(uname -r)/kernel/samples/rust/rust_minimal.ko test_int=2 test_str=world
+//! ```
+//!
+//! or via kernel cmdline with module dotted notation (when built-in and not built as a module):
+//!
+//! ```
+//! ... rust_minimal.test_int=2 rust_minimal.test_str=world ...
+//! ```
 
 use kernel::prelude::*;
 
@@ -11,10 +28,14 @@
     description: "Rust minimal sample",
     license: "GPL",
     params: {
-        test_parameter: i64 {
+        test_int: i64 {
             default: 1,
             description: "This parameter has a default of 1",
         },
+        test_str: string {
+            default: "hello",
+            description: "This parameter has a default of hello",
+        }
     },
 }
 
@@ -26,9 +47,13 @@ impl kernel::Module for RustMinimal {
     fn init(_module: &'static ThisModule) -> Result<Self> {
         pr_info!("Rust minimal sample (init)\n");
         pr_info!("Am I built-in? {}\n", !cfg!(MODULE));
+        pr_info!("test_int: {}\n", *module_parameters::test_int.value());
         pr_info!(
-            "test_parameter: {}\n",
-            *module_parameters::test_parameter.value()
+            "test_str: {}\n",
+            module_parameters::test_str
+                .value()
+                .as_cstr()
+                .expect("test_str has a default value")
         );
 
         let mut numbers = KVec::new();
-- 
2.52.0