Re: [PATCH v3 2/7] rust: property: Enable printing fwnode name and path

[Danilo Krummrich <dakr@kernel.org>]

On Fri, Apr 25, 2025 at 05:01:25PM +0200, Remo Senekowitsch wrote:
> Add two new public methods `display_name` and `display_path` to
> `FwNode`. They can be used by driver authors for logging purposes. In
> addition, they will be used by core property abstractions for automatic
> logging, for example when a driver attempts to read a required but
> missing property.
> 
> Signed-off-by: Remo Senekowitsch <remo@buenzli.dev>
> ---
>  rust/kernel/device/property.rs | 78 ++++++++++++++++++++++++++++++++++
>  1 file changed, 78 insertions(+)
> 
> diff --git a/rust/kernel/device/property.rs b/rust/kernel/device/property.rs
> index d89715f7d..28850aa3b 100644
> --- a/rust/kernel/device/property.rs
> +++ b/rust/kernel/device/property.rs
> @@ -49,6 +49,84 @@ pub(crate) fn as_raw(&self) -> *mut bindings::fwnode_handle {
>          self.0.get()
>      }
>  
> +    /// Returns an object that implements [`Display`](core::fmt::Display) for
> +    /// printing the name of a node.
> +    pub fn display_name(&self) -> impl core::fmt::Display + '_ {
> +        struct FwNodeDisplayName<'a>(&'a FwNode);
> +
> +        impl core::fmt::Display for FwNodeDisplayName<'_> {
> +            fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
> +                // SAFETY: self is valid by its type invariant
> +                let name = unsafe { bindings::fwnode_get_name(self.0.as_raw()) };
> +                if name.is_null() {
> +                    return Ok(());
> +                }
> +                // SAFETY: fwnode_get_name returns null or a valid C string and
> +                // name is not null
> +                let name = unsafe { CStr::from_char_ptr(name) };
> +                write!(f, "{name}")
> +            }
> +        }
> +
> +        FwNodeDisplayName(self)
> +    }
> +
> +    /// Returns an object that implements [`Display`](core::fmt::Display) for
> +    /// printing the full path of a node.
> +    pub fn display_path(&self) -> impl core::fmt::Display + '_ {
> +        struct FwNodeDisplayPath<'a>(&'a FwNode);
> +
> +        impl core::fmt::Display for FwNodeDisplayPath<'_> {
> +            fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
> +                // The logic here is the same as the one in lib/vsprintf.c
> +                // (fwnode_full_name_string).
> +
> +                let num_parents = unsafe { bindings::fwnode_count_parents(self.0.as_raw()) };
> +
> +                for depth in (0..=num_parents).rev() {
> +                    let fwnode = if depth == 0 {
> +                        self.0.as_raw()
> +                    } else {
> +                        // SAFETY: `self.0.as_raw()` is valid
> +                        unsafe { bindings::fwnode_get_nth_parent(self.0.as_raw(), depth) }
> +                    };
> +
> +                    // SAFETY: fwnode is valid, it is either `self.0.as_raw()` or
> +                    // the return value of `bindings::fwnode_get_nth_parent` which
> +                    // returns a valid pointer to a fwnode_handle if the provided
> +                    // depth is within the valid range, which we know to be true.
> +                    let prefix = unsafe { bindings::fwnode_get_name_prefix(fwnode) };
> +                    if !prefix.is_null() {
> +                        // SAFETY: fwnode_get_name_prefix returns null or a
> +                        // valid C string
> +                        let prefix = unsafe { CStr::from_char_ptr(prefix) };
> +                        write!(f, "{prefix}")?;
> +                    }
> +                    // SAFETY: fwnode is valid for the reasons stated above
> +                    let name = unsafe { bindings::fwnode_get_name(fwnode) };
> +                    if !name.is_null() {
> +                        // SAFETY: fwnode_get_name returns null or a valid
> +                        // C string
> +                        let name = unsafe { CStr::from_char_ptr(name) };
> +                        write!(f, "{name}")?;
> +                    }

I think you should be able to just call

	FwNodeDisplayName(self).fmt(f)?

for this part, which saves you the duplicated code.