Re: [PATCH v4 2/2] rust: zpool: add abstraction for zpool drivers

[Vitaly Wool]

> On Aug 26, 2025, at 7:02 PM, Benno Lossin <lossin@xxxxxxxxxx> wrote:
> 
> On Sat Aug 23, 2025 at 3:05 PM CEST, Vitaly Wool wrote:
>> +pub trait ZpoolDriver {
>> +    /// Opaque Rust representation of `struct zpool`.
>> +    type Pool: ForeignOwnable;
> 
> I think this is the same question that Danilo asked a few versions ago,
> but why do we need this? Why can't we just use `Self` instead?

It’s convenient to use it in the backend implementation, like in the toy example supplied in the documentation part:

+/// struct MyZpool {
+///     name: &'static CStr,
+///     bytes_used: AtomicU64,
+/// }
…
+/// impl ZpoolDriver for MyZpoolDriver {
+///     type Pool = KBox<MyZpool>;

Does that make sense?
 
> 
>> +
>> +    /// Create a pool.
>> +    fn create(name: &'static CStr, gfp: Flags) -> Result<Self::Pool>;
>> +
>> +    /// Destroy the pool.
>> +    fn destroy(pool: Self::Pool);
> 
> This should just be done via the normal `Drop` trait?

Let me check if I’m getting you right here. I take what you are suggesting is that we require that Pool implements Drop trait and then just do something like:

    extern "C" fn destroy_(pool: *mut c_void) {
        // SAFETY: The pointer originates from an `into_foreign` call.
        unsafe { drop(T::Pool::from_foreign(pool)) }
    }

Is that understanding correct?

~Vitaly


> 
> ---
> Cheers,
> Benno
> 
>> +
>> +    /// Allocate an object of size `size` bytes from `pool`, with the allocation flags `gfp` and
>> +    /// preferred NUMA node `nid`. If the allocation is successful, an opaque handle is returned.
>> +    fn malloc(
>> +        pool: <Self::Pool as ForeignOwnable>::BorrowedMut<'_>,
>> +        size: usize,
>> +        gfp: Flags,
>> +        nid: NumaNode,
>> +    ) -> Result<usize>;
>