Commit ef4dc4cc authored by Wedson Almeida Filho's avatar Wedson Almeida Filho Committed by Miguel Ojeda

rust: error: Add from_result() helper

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: default avatarFox Chen <foxhlchen@gmail.com>
Signed-off-by: default avatarFox Chen <foxhlchen@gmail.com>
Co-developed-by: default avatarMiguel Ojeda <ojeda@kernel.org>
Signed-off-by: default avatarMiguel Ojeda <ojeda@kernel.org>
Signed-off-by: default avatarWedson Almeida Filho <wedsonaf@gmail.com>
Reviewed-by: default avatarMartin Rodriguez Reboredo <yakoyoku@gmail.com>
Signed-off-by: default avatarAsahi Lina <lina@asahilina.net>
Link: https://lore.kernel.org/r/20230224-rust-error-v3-6-03779bddc02b@asahilina.netSigned-off-by: default avatarMiguel Ojeda <ojeda@kernel.org>
parent 752417b3
......@@ -237,3 +237,42 @@ 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),
}
}
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