linux-kernel - [PATCH 2/5] rust: error: Add Error::from_kernel

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Message-Id: <20230224-rust-error-v1-2-f8f9a9a87303@asahilina.net>
Date:   Fri, 24 Feb 2023 17:50:20 +0900
From:   Asahi Lina <lina@...hilina.net>
To:     Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Sven Van Asbroeck <thesven73@...il.com>
Cc:     Fox Chen <foxhlchen@...il.com>, rust-for-linux@...r.kernel.org,
        linux-kernel@...r.kernel.org, asahi@...ts.linux.dev,
        Asahi Lina <lina@...hilina.net>
Subject: [PATCH 2/5] rust: error: Add Error::from_kernel_errno()

From: Miguel Ojeda <ojeda@...nel.org>

Add a function to create `Error` values out of a kernel error return,
which safely upholds the invariant that the error code is well-formed
(negative and greater than -MAX_ERRNO). If a malformed code is passed
in, it will be converted to EINVAL.

Lina: Imported from rust-for-linux/rust as authored by Miguel and Fox
with refactoring from Wedson.

Co-developed-by: Fox Chen <foxhlchen@...il.com>
Signed-off-by: Fox Chen <foxhlchen@...il.com>
Co-developed-by: Wedson Almeida Filho <wedsonaf@...il.com>
Signed-off-by: Wedson Almeida Filho <wedsonaf@...il.com>
Signed-off-by: Miguel Ojeda <ojeda@...nel.org>
Signed-off-by: Asahi Lina <lina@...hilina.net>
---
 rust/kernel/error.rs | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/rust/kernel/error.rs b/rust/kernel/error.rs
index 8611758e27f4..3b439fdb405c 100644
--- a/rust/kernel/error.rs
+++ b/rust/kernel/error.rs
@@ -72,6 +72,25 @@ pub mod code {
 pub struct Error(core::ffi::c_int);
 
 impl Error {
+    /// Creates an [`Error`] from a kernel error code.
+    ///
+    /// It is a bug to pass an out-of-range `errno`. `EINVAL` would
+    /// be returned in such a case.
+    pub(crate) fn from_kernel_errno(errno: core::ffi::c_int) -> Error {
+        if errno < -(bindings::MAX_ERRNO as i32) || errno >= 0 {
+            // TODO: Make it a `WARN_ONCE` once available.
+            crate::pr_warn!(
+                "attempted to create `Error` with out of range `errno`: {}",
+                errno
+            );
+            return code::EINVAL;
+        }
+
+        // INVARIANT: The check above ensures the type invariant
+        // will hold.
+        Error(errno)
+    }
+
     /// Returns the kernel error code.
     pub fn to_kernel_errno(self) -> core::ffi::c_int {
         self.0

-- 
2.35.1