Re: [PATCH v2 03/11] rust: io: use pointer types instead of address

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

On Mon Apr 27, 2026 at 3:20 PM BST, Andreas Hindborg wrote:
> Gary Guo <gary@garyguo.net> writes:
>
>> This carries the size information with the pointer type and metadata, makes
>> it possible to use I/O projections and paves the way for IO view types.
>>
>> With this change, minimum size information becomes available through types;
>> so `KnownSize::MIN_SIZE` can be used and `IoKnownSize` trait is no longer
>> necessary. The trait is kept for compatibility and can be removed when
>> users stop using it for bounds.
>>
>> PCI config space uses only offsets and not pointers like MMIO; for this
>> null pointers (with proper size metadata) is used. This is okay as I/O
>> trait impl and I/O projections can operate on invalid pointers, and for PCI
>> config space we will only use address info and ignore the provenance.
>>
>> Signed-off-by: Gary Guo <gary@garyguo.net>
>> ---
>>  rust/kernel/devres.rs |   2 +-
>>  rust/kernel/io.rs     | 123 +++++++++++++++++++++-----------------------------
>>  rust/kernel/io/mem.rs |   2 +-
>>  rust/kernel/pci/io.rs |  74 ++++++++++++++++++------------
>>  4 files changed, 99 insertions(+), 102 deletions(-)
>>
>> diff --git a/rust/kernel/devres.rs b/rust/kernel/devres.rs
>> index 3e22c63efb98..ea86e9c62cdf 100644
>> --- a/rust/kernel/devres.rs
>> +++ b/rust/kernel/devres.rs
>> @@ -101,7 +101,7 @@ struct Inner<T> {
>>  /// impl<const SIZE: usize> Drop for IoMem<SIZE> {
>>  ///     fn drop(&mut self) {
>>  ///         // SAFETY: `self.0.addr()` is guaranteed to be properly mapped by `Self::new`.
>> -///         unsafe { bindings::iounmap(self.0.addr() as *mut c_void); };
>> +///         unsafe { bindings::iounmap(self.0.as_ptr().cast()); };
>>  ///     }
>>  /// }
>>  ///
>> diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
>> index 0b9c97c0a1d7..1682f2a0d20d 100644
>> --- a/rust/kernel/io.rs
>> +++ b/rust/kernel/io.rs
>> @@ -105,8 +105,8 @@ pub fn new_region(addr: usize, size: usize) -> Result<Self> {
>>  impl<T: ?Sized + KnownSize> MmioRaw<T> {
>>      /// Returns the base address of the MMIO region.
>>      #[inline]
>> -    pub fn addr(&self) -> usize {
>> -        self.addr.addr()
>> +    pub fn as_ptr(&self) -> *mut T {
>> +        self.addr
>>      }
>>  
>>      /// Returns the size of the MMIO region.
>> @@ -166,7 +166,7 @@ pub fn size(&self) -> usize {
>>  /// impl<const SIZE: usize> Drop for IoMem<SIZE> {
>>  ///     fn drop(&mut self) {
>>  ///         // SAFETY: `self.0.addr()` is guaranteed to be properly mapped by `Self::new`.
>> -///         unsafe { bindings::iounmap(self.0.addr() as *mut c_void); };
>> +///         unsafe { bindings::iounmap(self.0.as_ptr().cast()); };
>>  ///     }
>>  /// }
>>  ///
>> @@ -217,14 +217,14 @@ pub trait IoCapable<T> {
>>      /// # Safety
>>      ///
>>      /// The range `[address..address + size_of::<T>()]` must be within the bounds of `Self`.
>> -    unsafe fn io_read(&self, address: usize) -> T;
>> +    unsafe fn io_read(&self, address: *mut T) -> T;
>>  
>>      /// Performs an I/O write of `value` at `address`.
>>      ///
>>      /// # Safety
>>      ///
>>      /// The range `[address..address + size_of::<T>()]` must be within the bounds of `Self`.
>> -    unsafe fn io_write(&self, value: T, address: usize);
>> +    unsafe fn io_write(&self, value: T, address: *mut T);
>>  }
>>  
>
> In v1 you had a requirement for `address` to be aligned. Why did you
> drop that?

In v1 Alex wants me to split this part to a separate commit as this is a
pre-existing requirement that is just not documented. The patch 4 is that
change.

Best,
Gary

>
>
> Best regards,
> Andreas Hindborg