zephyr: Add Error and Result types

Create a simple error type to handle Zephyr errors.  This can be
expanded in the future to better be able to distinguish the errors, but
this allows us to properly return values from wrapped functions.

Signed-off-by: David Brown <[email protected]>

Author: d3zd3z

zephyr-sys/build.rs

@@ -71,6 +71,7 @@ fn main() -> Result<()> {
         .allowlist_function("k_.*")
         .allowlist_function("gpio_.*")
         .allowlist_function("sys_.*")
+        .allowlist_item("E.*")
         .allowlist_item("ZR_.*")
         // Deprecated
         .blocklist_function("sys_clock_timeout_end_calc")

zephyr/src/error.rs

@@ -0,0 +1,56 @@
+// Copyright (c) 2024 Linaro LTD
+// SPDX-License-Identifier: Apache-2.0
+
+//! # Zephyr errors
+//!
+//! This module contains an `Error` and `Result` type for use in wrapped Zephyr calls.  Many
+//! operations in Zephyr return an int result where negative values correspond with errnos.
+//! Convert those to a `Result` type where the `Error` condition maps to errnos.
+//!
+//! Initially, this will just simply wrap the numeric error code, but it might make sense to make
+//! this an enum itself, however, it would probably be better to auto-generate this enum instead of
+//! trying to maintain the list manually.
+
+use core::ffi::c_int;
+use core::fmt;
+
+// This is a little messy because the constants end up as u32 from bindgen, although the values are
+// negative.
+
+/// A Zephyr error.
+///
+/// Represents an error result returned within Zephyr.
+pub struct Error(pub u32);
+
+impl core::error::Error for Error {}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "zephyr error errno:{}", self.0)
+    }
+}
+
+impl fmt::Debug for Error {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "zephyr error errno:{}", self.0)
+    }
+}
+
+/// Wraps a value with a possible Zephyr error.
+pub type Result<T> = core::result::Result<T, Error>;
+
+/// Map a return result from Zephyr into an Result.
+///
+/// Negative return results being considered errors.
+pub fn to_result(code: c_int) -> Result<c_int> {
+    if code < 0 {
+        Err(Error(code as u32))
+    } else {
+        Ok(code)
+    }
+}
+
+/// Map a return result, with a void result.
+pub fn to_result_void(code: c_int) -> Result<()> {
+    to_result(code).map(|_| ())
+}

zephyr/src/lib.rs

@@ -85,11 +85,14 @@
 #![allow(unexpected_cfgs)]
 
 pub mod align;
+pub mod error;
 pub mod object;
 pub mod sync;
 pub mod sys;
 pub mod time;
 
+pub use error::{Error, Result};
+
 // Bring in the generated kconfig module
 include!(concat!(env!("OUT_DIR"), "/kconfig.rs"));