Re: [PATCH v2 1/1] rust: simplify `Adapter::id_info`

["Gary Guo" <gary@garyguo.net>]

On Sat Jan 17, 2026 at 12:53 PM GMT, Danilo Krummrich wrote:
> On Sat Jan 17, 2026 at 1:07 PM CET, Greg KH wrote:
>> Does clippy complain about this one?
>
> No, it does not.
>
>> I don't have strong feelings either, but the original is "easier" for
>> those of us used to C code.
>
> I think it's a matter of preference. Personally, I like those functional
> characteristics of Rust and the corresponding possibility of compact expressions
> as long as it is not overdone.
>
> This case seems pretty simple though. :)
>
> In comparison, this is code from allocating the level 1 page directory for the
> GSP (radix3) firmware, which is probably a bit too much.
>
> 	level1 <- {
> 	    // Allocate the level 1 page table, map the level 2 page table onto it, and map it
> 	    // into the device address space.
> 	    VVec::<u8>::with_capacity(
> 	        level2.iter().count() * size_of::<u64>(),
> 	        GFP_KERNEL,
> 	    )
> 	    .map_err(|_| ENOMEM)
> 	    .and_then(|level1| map_into_lvl(&level2, level1))
> 	    .map(|level1| SGTable::new(dev, level1, DataDirection::ToDevice, GFP_KERNEL))?

For this specific instance, it looks like it could just be

    let level1 = VVec::<u8>::with_capacity(
        level2.iter().count() * size_of::<u64>(),
        GFP_KERNEL,
    )?;
    let level1 = map_into_lvl(&level2, level1)?;
    SGTable::new(dev, level1, DataDirection::ToDevice, GFP_KENREL)?

which IMO looks clearer.
    
I suspect what people want is Elixir's pipe operator so the above is like this
(non-existent, imaginary syntax):

    VVec::<u8>::with_capacity(
        level2.iter().count() * size_of::<u64>(),
        GFP_KERNEL,
    )?
    |> map_into_lvl(&level2, _)?
    |> SGTable::new(dev, _, DataDirection::ToDevice, GFP_KERNEL)?

But I think keeping things as `Result` (and not using `?`) just to use the
functional combinatiors is probably a bad idea.

Best,
Gary