> On May 20, 2025, at 11:37 AM, Danilo Krummrich <d...@kernel.org> wrote:
>
> On Tue, May 20, 2025 at 11:11:12AM -0400, Joel Fernandes wrote:
>> On 5/20/2025 11:01 AM, Danilo Krummrich wrote:
>>
>> I made this change and it LGTM. Thanks! I did not do the '.0' though since I
>> want to keep the readability, lets see in the next revision if that looks
>> good.
>
> I think readability, is just as good with `.0`, but I'm fine with either.
Cool.
>
>>>>> In general, I feel like a lot of those Option come from a programming
>>>>> pattern
>>>>> that is very common in C, i.e. allocate a structure (stack or heap) and
>>>>> then
>>>>> initialize its fields.
>>>>>
>>>>> In Rust you should aim to initialize all the fields of a structure when
>>>>> you
>>>>> create the instance. Option as a return type of a function is common, but
>>>>> it's
>>>>> always a bit suspicious when there is an Option field in a struct.
>>>>
>>>> I looked into it, I could not git rid of those ones because we need to
>>>> initialize in the "impl TryFrom<BiosImageBase> for BiosImage {"
>>>>
>>>> 0xE0 => Ok(BiosImage::FwSec(FwSecBiosImage {
>>>> base,
>>>> falcon_data_offset: None,
>>>> pmu_lookup_table: None,
>>>> falcon_ucode_offset: None,
>>>> })),
>>>>
>>>> And these fields will not be determined until much later, because as is
>>>> the case
>>>> with the earlier example, these fields cannot be determined until all the
>>>> images
>>>> are parsed.
>>>
>>> You should not use TryFrom, but instead use a normal constructor, such as
>>>
>>> BiosImage::new(base_bios_image)
>>>
>>> and do the parsing within this constructor.
>>>
>>> If you want a helper type with Options while parsing that's totally fine,
>>> but
>>> the final result can clearly be without Options. For instance:
>>>
>>> struct Data {
>>> image: KVec<u8>,
>>> }
>>>
>>> impl Data {
>>> fn new() -> Result<Self> {
>>> let parser = DataParser::new();
>>>
>>> Self { image: parser.parse()? }
>>> }
>>>
>>> fn load_image(&self) {
>>> ...
>>> }
>>> }
>>>
>>> struct DataParser {
>>> // Only some images have a checksum.
>>> checksum: Option<u64>,
>>> // Some images have an extra offset.
>>> offset: Option<u64>,
>>> // Some images need to be patched.
>>> patch: Option<KVec<u8>>,
>>> image: KVec<u8>,
>>> }
>>>
>>> impl DataParser {
>>> fn new() -> Self {
>>> Self {
>>> checksum: None,
>>> offset: None,
>>> patch: None,
>>> bytes: KVec::new(),
>>> }
>>> }
>>>
>>> fn parse(self) -> Result<KVec<u8>> {
>>> // Fetch all the required data.
>>> self.fetch_checksum()?;
>>> self.fetch_offset()?;
>>> self.fetch_patch()?;
>>> self.fetch_byes()?;
>>>
>>> // Doesn't do anything if `checksum == None`.
>>> self.validate_checksum()?;
>>>
>>> // Doesn't do anything if `offset == None`.
>>> self.apply_offset()?;
>>>
>>> // Doesn't do anything if `patch == None`.
>>> self.apply_patch()?;
>>>
>>> // Return the final image.
>>> self.image
>>> }
>>> }
>>>
>>> I think the pattern here is the same, but in this example you keep working
>>> with
>>> the DataParser, instead of a new instance of Data.
>>
>> I think this would be a fundamental rewrite of the patch. I am Ok with
>> looking
>> into it as a future item, but right now I am not sure if it justifies not
>> using
>> Option for these few. There's a lot of immediate work we have to do for boot,
>> lets please not block the patch on just this if that's Ok with you. If you
>> want,
>> I could add a TODO here.
>
> Honestly, I don't think it'd be too bad to fix this up. It's "just" a bit of
> juggling fields and moving code around. The actual code should not change
> much.
>
> Having Option<T> where the corresponding value T isn't actually optional is
> extremely confusing and makes it hard for everyone, but especially new
> contributors, to understand the code and can easily trick people into taking
> wrong assumptions.
>
> Making the code reasonably accessible for (new) contributors is one of the
> objectives of nova and one of the learnings from nouveau.
>
> Hence, let's get this right from the get-go please.
Ok, I will look into making this change. :-)
thanks,
- Joel
