bindings: rust: provide LineRequest::chip_name()

Provide a wrapper around gpiod_line_request_get_chip_name() for Rust
bindings and add a test-case.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Erik Schilling <erik.schilling@linaro.org>
Reviewed-by: Kent Gibson <warthog618@gmail.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>

bindings/rust/libgpiod/src/line_request.rs

@@ -2,6 +2,7 @@
 // SPDX-FileCopyrightText: 2022 Linaro Ltd.
 // SPDX-FileCopyrightText: 2022 Viresh Kumar <viresh.kumar@linaro.org>
 
+use std::ffi::CStr;
 use std::os::unix::prelude::AsRawFd;
 use std::time::Duration;
 
@@ -25,6 +26,19 @@ impl Request {
         Ok(Self { request })
     }
 
+    /// Get the name of the chip this request was made on.
+    pub fn chip_name(&self) -> Result<&str> {
+        // SAFETY: The `gpiod_line_request` is guaranteed to be live as long
+        // as `&self`
+        let name = unsafe { gpiod::gpiod_line_request_get_chip_name(self.request) };
+
+        // SAFETY: The string is guaranteed to be valid, non-null and immutable
+        // by the C API for the lifetime of the `gpiod_line_request`.
+        unsafe { CStr::from_ptr(name) }
+            .to_str()
+            .map_err(Error::StringNotUtf8)
+    }
+
     /// Get the number of lines in the request.
     pub fn num_lines(&self) -> usize {
         // SAFETY: `gpiod_line_request` is guaranteed to be valid here.

bindings/rust/libgpiod/tests/line_request.rs

@@ -59,6 +59,20 @@ mod line_request {
     mod verify {
         use super::*;
 
+        #[test]
+        fn chip_name() {
+            const GPIO: Offset = 2;
+            let mut config = TestConfig::new(NGPIO).unwrap();
+            config.lconfig_add_settings(&[GPIO]);
+            config.request_lines().unwrap();
+
+            let arc = config.sim();
+            let sim = arc.lock().unwrap();
+            let chip_name = sim.chip_name().clone();
+
+            assert_eq!(config.request().chip_name().unwrap(), chip_name);
+        }
+
         #[test]
         fn custom_consumer() {
             const GPIO: Offset = 2;