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authorSven Van Asbroeck <thesven73@gmail.com>2023-04-03 18:48:14 +0900
committerMiguel Ojeda <ojeda@kernel.org>2023-04-12 18:41:04 +0200
commit752417b3f0e7721f1d630f40da22d57e0dae043e (patch)
tree5baa8b2da6389cb02f89b4e58ac3957c8f9b0274 /rust
parent086fbfa3b328901fa8b369093ba468864e20544e (diff)
rust: error: Add a helper to convert a C ERR_PTR to a `Result`
Some kernel C API functions return a pointer which embeds an optional `errno`. Callers are supposed to check the returned pointer with `IS_ERR()` and if this returns `true`, retrieve the `errno` using `PTR_ERR()`. Create a Rust helper function to implement the Rust equivalent: transform a `*mut T` to `Result<*mut T>`. Lina: Imported from rust-for-linux/linux, with subsequent refactoring and contributions squashed in and attributed below. Renamed the function to from_err_ptr(). Co-developed-by: Boqun Feng <boqun.feng@gmail.com> Signed-off-by: Boqun Feng <boqun.feng@gmail.com> Co-developed-by: Miguel Ojeda <ojeda@kernel.org> Signed-off-by: Miguel Ojeda <ojeda@kernel.org> Co-developed-by: Fox Chen <foxhlchen@gmail.com> Signed-off-by: Fox Chen <foxhlchen@gmail.com> Co-developed-by: Gary Guo <gary@garyguo.net> Signed-off-by: Gary Guo <gary@garyguo.net> Signed-off-by: Sven Van Asbroeck <thesven73@gmail.com> Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com> Signed-off-by: Asahi Lina <lina@asahilina.net> Link: https://lore.kernel.org/r/20230224-rust-error-v3-5-03779bddc02b@asahilina.net [ Add a removal of `#[allow(dead_code)]`. ] Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Diffstat (limited to 'rust')
-rw-r--r--rust/helpers.c12
-rw-r--r--rust/kernel/error.rs50
2 files changed, 61 insertions, 1 deletions
diff --git a/rust/helpers.c b/rust/helpers.c
index 89f4cd1e0df3..04b9be46e887 100644
--- a/rust/helpers.c
+++ b/rust/helpers.c
@@ -53,6 +53,18 @@ __force void *rust_helper_ERR_PTR(long err)
}
EXPORT_SYMBOL_GPL(rust_helper_ERR_PTR);
+bool rust_helper_IS_ERR(__force const void *ptr)
+{
+ return IS_ERR(ptr);
+}
+EXPORT_SYMBOL_GPL(rust_helper_IS_ERR);
+
+long rust_helper_PTR_ERR(__force const void *ptr)
+{
+ return PTR_ERR(ptr);
+}
+EXPORT_SYMBOL_GPL(rust_helper_PTR_ERR);
+
/*
* We use `bindgen`'s `--size_t-is-usize` option to bind the C `size_t` type
* as the Rust `usize` type, so we can use it in contexts where Rust
diff --git a/rust/kernel/error.rs b/rust/kernel/error.rs
index 7e25871063df..67637b874267 100644
--- a/rust/kernel/error.rs
+++ b/rust/kernel/error.rs
@@ -96,7 +96,6 @@ impl Error {
/// # Safety
///
/// `errno` must be within error code range (i.e. `>= -MAX_ERRNO && < 0`).
- #[allow(dead_code)]
unsafe fn from_errno_unchecked(errno: core::ffi::c_int) -> Error {
// INVARIANT: The contract ensures the type invariant
// will hold.
@@ -189,3 +188,52 @@ pub fn to_result(err: core::ffi::c_int) -> Result {
Ok(())
}
}
+
+/// Transform a kernel "error pointer" to a normal pointer.
+///
+/// Some kernel C API functions return an "error pointer" which optionally
+/// embeds an `errno`. Callers are supposed to check the returned pointer
+/// for errors. This function performs the check and converts the "error pointer"
+/// to a normal pointer in an idiomatic fashion.
+///
+/// # Examples
+///
+/// ```ignore
+/// # use kernel::from_err_ptr;
+/// # use kernel::bindings;
+/// fn devm_platform_ioremap_resource(
+/// pdev: &mut PlatformDevice,
+/// index: u32,
+/// ) -> Result<*mut core::ffi::c_void> {
+/// // SAFETY: FFI call.
+/// unsafe {
+/// from_err_ptr(bindings::devm_platform_ioremap_resource(
+/// pdev.to_ptr(),
+/// index,
+/// ))
+/// }
+/// }
+/// ```
+// TODO: Remove `dead_code` marker once an in-kernel client is available.
+#[allow(dead_code)]
+pub(crate) fn from_err_ptr<T>(ptr: *mut T) -> Result<*mut T> {
+ // CAST: Casting a pointer to `*const core::ffi::c_void` is always valid.
+ let const_ptr: *const core::ffi::c_void = ptr.cast();
+ // SAFETY: The FFI function does not deref the pointer.
+ if unsafe { bindings::IS_ERR(const_ptr) } {
+ // SAFETY: The FFI function does not deref the pointer.
+ let err = unsafe { bindings::PTR_ERR(const_ptr) };
+ // CAST: If `IS_ERR()` returns `true`,
+ // then `PTR_ERR()` is guaranteed to return a
+ // negative value greater-or-equal to `-bindings::MAX_ERRNO`,
+ // which always fits in an `i16`, as per the invariant above.
+ // And an `i16` always fits in an `i32`. So casting `err` to
+ // an `i32` can never overflow, and is always valid.
+ //
+ // SAFETY: `IS_ERR()` ensures `err` is a
+ // negative value greater-or-equal to `-bindings::MAX_ERRNO`.
+ #[allow(clippy::unnecessary_cast)]
+ return Err(unsafe { Error::from_errno_unchecked(err as core::ffi::c_int) });
+ }
+ Ok(ptr)
+}