Re: [PATCH v8 2/2] rust: xarray: Add an abstraction for XArray

[John Hubbard <jhubbard@nvidia.com>]

On 3/21/24 6:20 PM, Boqun Feng wrote:
> On Thu, Mar 21, 2024 at 05:22:11PM -0700, John Hubbard wrote:
>> On 3/19/24 2:32 AM, Philipp Stanner wrote:
>> ...
>>>>
>>>>> +        if ret < 0 {
>>>>> +            Err(Error::from_errno(ret))
>>>>> +        } else {
>>>>> +            guard.dismiss();
>>>>> +            Ok(id as usize)
>>>>> +        }
>>>>
>>>> You could make this easier to read using to_result.
>>>>
>>>> to_result(ret)?;
>>>> guard.dismiss();
>>>> Ok(id as usize)
>>>
>>> My 2 cents, I'd go for classic kernel style:
>>>
>>>
>>> if ret < 0 {
>>>       return Err(...);
>>> }
>>>
>>> guard.dismiss();
>>> Ok(id as usize)
>>>
>>
>> Yes.
>>
>> As a "standard" C-based kernel person who is trying to move into Rust
>> for Linux, I hereby invoke my Rust-newbie powers to confirm that the
>> "clasic kernel style" above goes into my head much faster and easier,
>> yes. :)
>>
> 
> Hope I'm still belong to a "standard C-based kernel person" ;-) My
> problem on "if ret < 0 { ... }" is: what's the type of "ret", and is it
> "negative means failure" or "non-zero means failure"? Now for this
> particular code, the assignment of "ret" and the use of "ret" is pretty
> close, so it doesn't matter. But in the code where "ret" is used for
> multiple function calls and there is code in-between, then I'd prefer we
> use `to_result` (i.e. `Result` type and question mark operator).

No argument there. I was more focused on the readability of: do a clean
check for failure, and returning directly in that case. And then
continuing on with non-failure-case code. The to_result() part makes
sense and can fit right into that.

  
>> I hope I'm not violating any "this is how Rust idioms must be"
>> conventions. But if not, then all other things being equal, it is of
>> course a nice touch to make the code more readable to the rest of the
>> kernel folks.
>>
> 
> One more extra point from myself only: if one is using Rust for drivers
> or subsystem they are going to take care of it in the future, it's
> totally fine for them to pick coding styles that they feel comfortable,
> I don't want to make people who do the real work feel frustrated because
> "this is how Rust idioms must be", also I don't believe tools should
> restrict people. But in the "kernel" crate (i.e. for core kernel part),
> I want to make it "Rusty" since it's the point of the experiement ("you
> asked for it ;-)).
>

OK, I understand that reasoning.
  
> Hope we can find a balanced point when we learn more and more ;-)

Yes. And to continue with the metaphor, I'm attempting here to put a
light thumb on the scale. :)


thanks,
-- 
John Hubbard
NVIDIA