diff mbox series

[v2,6/6] rust: error: Add from_result() helper

Message ID 20230224-rust-error-v2-6-3900319812da@asahilina.net
State New
Headers
Series rust: error: Add missing wrappers to convert to/from kernel error codes |

Commit Message

Asahi Lina March 29, 2023, 12:04 p.m. UTC 
  From: Wedson Almeida Filho <wedsonaf@gmail.com>

Add a helper function to easily return C result codes from a Rust function
that calls functions which return a Result<T>.

Lina: Imported from rust-for-linux/rust, originally developed by Wedson
as part of file_operations.rs. Added the allow() flags since there is no
user in the kernel crate yet and fixed a typo in a comment. Replaced the
macro with a function taking a closure, per discussion on the ML.

Co-developed-by: Fox Chen <foxhlchen@gmail.com>
Signed-off-by: Fox Chen <foxhlchen@gmail.com>
Co-developed-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Wedson Almeida Filho <wedsonaf@gmail.com>
Signed-off-by: Asahi Lina <lina@asahilina.net>
---
 rust/kernel/error.rs | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

Comments

Martin Rodriguez Reboredo March 29, 2023, 2:55 p.m. UTC | #1 
On 3/29/23 09:04, Asahi Lina wrote:
> [...]
> 
> +
> +/// Calls a closure returning a [`crate::error::Result<T>`] and converts the result to
> +/// a C integer result.
> +///
> +/// This is useful when calling Rust functions that return [`crate::error::Result<T>`]
> +/// from inside `extern "C"` functions that need to return an integer error result.
> +///
> +/// `T` should be convertible from an `i16` via `From<i16>`.
> +///
> +/// # Examples
> +///
> +/// ```ignore
> +/// # use kernel::from_result;
> +/// # use kernel::bindings;
> +/// unsafe extern "C" fn probe_callback(
> +///     pdev: *mut bindings::platform_device,
> +/// ) -> core::ffi::c_int {
> +///     from_result(|| {
> +///         let ptr = devm_alloc(pdev)?;
> +///         bindings::platform_set_drvdata(pdev, ptr);
> +///         Ok(0)
> +///     })
> +/// }
> +/// ```
> +// TODO: Remove `dead_code` marker once an in-kernel client is available.
> +#[allow(dead_code)]
> +pub(crate) fn from_result<T, F>(f: F) -> T
> +where
> +    T: From<i16>,
> +    F: FnOnce() -> Result<T>,
> +{
> +    match f() {
> +        Ok(v) => v,
> +        // NO-OVERFLOW: negative `errno`s are no smaller than `-bindings::MAX_ERRNO`,
> +        // `-bindings::MAX_ERRNO` fits in an `i16` as per invariant above,
> +        // therefore a negative `errno` always fits in an `i16` and will not overflow.
> +        Err(e) => T::from(e.to_errno() as i16),
> +    }
> +}
> 

Reviewed-by: Martin Rodriguez Reboredo
diff mbox series

Patch

diff --git a/rust/kernel/error.rs b/rust/kernel/error.rs
index 6b10129075a7..4d8b19d5967d 100644
--- a/rust/kernel/error.rs
+++ b/rust/kernel/error.rs
@@ -226,3 +226,42 @@  pub(crate) fn from_err_ptr<T>(ptr: *mut T) -> Result<*mut T> {
     }
     Ok(ptr)
 }
+
+/// Calls a closure returning a [`crate::error::Result<T>`] and converts the result to
+/// a C integer result.
+///
+/// This is useful when calling Rust functions that return [`crate::error::Result<T>`]
+/// from inside `extern "C"` functions that need to return an integer error result.
+///
+/// `T` should be convertible from an `i16` via `From<i16>`.
+///
+/// # Examples
+///
+/// ```ignore
+/// # use kernel::from_result;
+/// # use kernel::bindings;
+/// unsafe extern "C" fn probe_callback(
+///     pdev: *mut bindings::platform_device,
+/// ) -> core::ffi::c_int {
+///     from_result(|| {
+///         let ptr = devm_alloc(pdev)?;
+///         bindings::platform_set_drvdata(pdev, ptr);
+///         Ok(0)
+///     })
+/// }
+/// ```
+// TODO: Remove `dead_code` marker once an in-kernel client is available.
+#[allow(dead_code)]
+pub(crate) fn from_result<T, F>(f: F) -> T
+where
+    T: From<i16>,
+    F: FnOnce() -> Result<T>,
+{
+    match f() {
+        Ok(v) => v,
+        // NO-OVERFLOW: negative `errno`s are no smaller than `-bindings::MAX_ERRNO`,
+        // `-bindings::MAX_ERRNO` fits in an `i16` as per invariant above,
+        // therefore a negative `errno` always fits in an `i16` and will not overflow.
+        Err(e) => T::from(e.to_errno() as i16),
+    }
+}