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

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Message-Id: <DA1UXY2O47Y2.1ND9MC6L01217@buenzli.dev>
Date: Wed, 21 May 2025 15:03:07 +0200
From: "Remo Senekowitsch" <remo@...nzli.dev>
To: "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>
Cc: "Rob Herring" <robh@...nel.org>, "Saravana Kannan"
 <saravanak@...gle.com>, "Miguel Ojeda" <ojeda@...nel.org>, "Alex Gaynor"
 <alex.gaynor@...il.com>, "Boqun Feng" <boqun.feng@...il.com>, "Gary Guo"
 <gary@...yguo.net>, Björn Roy Baron
 <bjorn3_gh@...tonmail.com>, "Benno Lossin" <benno.lossin@...ton.me>,
 "Andreas Hindborg" <a.hindborg@...nel.org>, "Alice Ryhl"
 <aliceryhl@...gle.com>, "Trevor Gross" <tmgross@...ch.edu>, "Danilo
 Krummrich" <dakr@...nel.org>, "Rafael J. Wysocki" <rafael@...nel.org>,
 "Dirk Behme" <dirk.behme@...bosch.com>, <linux-kernel@...r.kernel.org>,
 <devicetree@...r.kernel.org>, <rust-for-linux@...r.kernel.org>
Subject: Re: [PATCH v5 4/9] rust: device: Enable printing fwnode name and
 path

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@...nzli.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?