This constructor is public since commit 5ed147473458 ("rust: error:
make conversion functions public"), and we will refer to it from the
documentation of `to_result` in a later commit.

Thus improve its documentation, including adding examples.

Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
 rust/kernel/error.rs | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/error.rs b/rust/kernel/error.rs
index a41de293dcd1..c415c3d3a3b6 100644
--- a/rust/kernel/error.rs
+++ b/rust/kernel/error.rs
@@ -101,8 +101,23 @@ macro_rules! declare_err {
 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.
+    /// `errno` must be within error code range (i.e. `>= -MAX_ERRNO && < 0`).
+    ///
+    /// It is a bug to pass an out-of-range `errno`. [`code::EINVAL`] is returned in such a case.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// assert_eq!(Error::from_errno(-1), EPERM);
+    /// assert_eq!(Error::from_errno(-2), ENOENT);
+    /// ```
+    ///
+    /// The following calls are considered a bug:
+    ///
+    /// ```
+    /// assert_eq!(Error::from_errno(0), EINVAL);
+    /// assert_eq!(Error::from_errno(-1000000), EINVAL);
+    /// ```
     pub fn from_errno(errno: crate::ffi::c_int) -> Error {
         if let Some(error) = Self::try_from_errno(errno) {
             error
-- 
2.51.0

On Fri Aug 29, 2025 at 9:22 PM CEST, Miguel Ojeda wrote:
> This constructor is public since commit 5ed147473458 ("rust: error:
> make conversion functions public"), and we will refer to it from the
> documentation of `to_result` in a later commit.
>
> Thus improve its documentation, including adding examples.
>
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Reviewed-by: Benno Lossin <lossin@kernel.org>

---
Cheers,
Benno

> ---
>  rust/kernel/error.rs | 19 +++++++++++++++++--
>  1 file changed, 17 insertions(+), 2 deletions(-)

On Sat Aug 30, 2025 at 4:22 AM JST, Miguel Ojeda wrote:
> This constructor is public since commit 5ed147473458 ("rust: error:
> make conversion functions public"), and we will refer to it from the
> documentation of `to_result` in a later commit.
>
> Thus improve its documentation, including adding examples.
>
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

This reads very smoothly!

Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>

> ---
>  rust/kernel/error.rs | 19 +++++++++++++++++--
>  1 file changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/rust/kernel/error.rs b/rust/kernel/error.rs
> index a41de293dcd1..c415c3d3a3b6 100644
> --- a/rust/kernel/error.rs
> +++ b/rust/kernel/error.rs
> @@ -101,8 +101,23 @@ macro_rules! declare_err {
>  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.
> +    /// `errno` must be within error code range (i.e. `>= -MAX_ERRNO && < 0`).
> +    ///
> +    /// It is a bug to pass an out-of-range `errno`. [`code::EINVAL`] is returned in such a case.
> +    ///
> +    /// # Examples
> +    ///
> +    /// ```
> +    /// assert_eq!(Error::from_errno(-1), EPERM);
> +    /// assert_eq!(Error::from_errno(-2), ENOENT);

Small nit: this leaves a tiny chance of misunderstanding that this
function actually expects literal negative integers. How about using
e.g. `bindings::EPERM` instead of `-1`?

On Sat, Aug 30, 2025 at 2:18 PM Alexandre Courbot <acourbot@nvidia.com> wrote:
>
> Small nit: this leaves a tiny chance of misunderstanding that this
> function actually expects literal negative integers. How about using
> e.g. `bindings::EPERM` instead of `-1`?

Sounds good -- or perhaps `EPERM.to_errno()`?

Thanks!

Cheers,
Miguel

On Sat Aug 30, 2025 at 10:00 PM JST, Miguel Ojeda wrote:
> On Sat, Aug 30, 2025 at 2:18 PM Alexandre Courbot <acourbot@nvidia.com> wrote:
>>
>> Small nit: this leaves a tiny chance of misunderstanding that this
>> function actually expects literal negative integers. How about using
>> e.g. `bindings::EPERM` instead of `-1`?
>
> Sounds good -- or perhaps `EPERM.to_errno()`?

Looking good to me!