Re: [PATCH v5 4/9] rust: device: Enable printing fwnode name and path

["Remo Senekowitsch" <remo@buenzli.dev>]

On Wed May 21, 2025 at 2:02 PM CEST, Greg Kroah-Hartman wrote:
> On Tue, May 20, 2025 at 10:00:19PM +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 | 72 ++++++++++++++++++++++++++++++++++
>>  1 file changed, 72 insertions(+)
>> 
>> diff --git a/rust/kernel/device/property.rs b/rust/kernel/device/property.rs
>> index 70593343bd811..6ccc7947f9c31 100644
>> --- a/rust/kernel/device/property.rs
>> +++ b/rust/kernel/device/property.rs
>> @@ -32,6 +32,78 @@ 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(());
>
> So if there is no name, you are returning Ok()?  Are you sure that's ok
> to do?  What will the result of the string look like then?

In that case we're not writing anything to the formatter, which is
equivalent to an empty string. `Ok(())` means that writing succeeded.

I assumed that a valid node would always have a name. And we're
guaranteed to have a valid node. So I assumed this case would never
happen and didn't think too hard about it. But even if a valid node has
not name, empty string is probably the correct thing, right?