Re: [PATCH v5 01/20] rust: io: add dynamically-sized `Region` type

On Fri Jul 3, 2026 at 4:16 AM BST, Alexandre Courbot wrote:
> On Fri Jun 26, 2026 at 11:45 PM JST, Gary Guo wrote:
> <...>
>> diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
>> index fcc7678fd9e3..d1c5f0121994 100644
>> --- a/rust/kernel/io.rs
>> +++ b/rust/kernel/io.rs
>> @@ -6,7 +6,11 @@
>>  
>>  use crate::{
>>      bindings,
>> -    prelude::*, //
>> +    prelude::*,
>> +    ptr::{
>> +        Alignment,
>> +        KnownSize, //
>> +    }, //
>>  };
>>  
>>  pub mod mem;
>> @@ -31,6 +35,57 @@
>>  /// `CONFIG_PHYS_ADDR_T_64BIT`, and it can be a u64 even on 32-bit architectures.
>>  pub type ResourceSize = bindings::resource_size_t;
>>  
>> +/// Untyped I/O region.
>> +///
>> +/// This type can be used when an I/O region without known type information has a compile-time known
>> +/// minimum size (and a runtime known actual size).
>> +///
>> +/// # Invariants
>> +///
>> +/// - Size of the region is at least as large as the `SIZE` generic parameter.
>> +/// - Size of the region is multiple of 4.
>> +#[repr(C, align(4))]
>> +pub struct Region<const SIZE: usize = 0> {
>> +    inner: [u8],
>> +}
>> +
>> +impl<const SIZE: usize> Region<SIZE> {
>> +    /// Create a raw mutable pointer from given base address and size.
>> +    ///
>> +    /// `size` should be at least as large as the minimum size `SIZE`, and `base` and `size` should
>> +    /// be 4-byte aligned to uphold the type invariant.
>
> The second part of my comment on v4 was not relevant [1], but how about the
> "should -> must" proposal?

I think "should" is correct here. Most likely `size` satisfy the requirement,
but it's not UB or even logic error if `size` doesn't meet the requirement.

For example, it's okay to call this to get a raw pointer before performing
checks. As long as the pointer stays raw, it's not invalid.

Best,
Gary

>
> Regardless:
>
> Reviewed-by: Alexandre Courbot <[email protected]>
>
> [1] https://lore.kernel.org/all/[email protected]/