linux-kernel - Re: [PATCH v9 2/5] rust: io: factor common I/O helpers into Io trait

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <DFQ481S2NI1S.3HMMZMYEQ9QP8@garyguo.net>
Date: Fri, 16 Jan 2026 15:23:20 +0000
From: "Gary Guo" <gary@...yguo.net>
To: "Alice Ryhl" <aliceryhl@...gle.com>, "Zhi Wang" <zhiw@...dia.com>
Cc: <rust-for-linux@...r.kernel.org>, <linux-pci@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, <dakr@...nel.org>, <bhelgaas@...gle.com>,
 <kwilczynski@...nel.org>, <ojeda@...nel.org>, <alex.gaynor@...il.com>,
 <boqun.feng@...il.com>, <gary@...yguo.net>, <bjorn3_gh@...tonmail.com>,
 <lossin@...nel.org>, <a.hindborg@...nel.org>, <tmgross@...ch.edu>,
 <markus.probst@...teo.de>, <helgaas@...nel.org>, <cjia@...dia.com>,
 <smitra@...dia.com>, <ankita@...dia.com>, <aniketa@...dia.com>,
 <kwankhede@...dia.com>, <targupta@...dia.com>, <acourbot@...dia.com>,
 <joelagnelf@...dia.com>, <jhubbard@...dia.com>, <zhiwang@...nel.org>,
 <daniel.almeida@...labora.com>
Subject: Re: [PATCH v9 2/5] rust: io: factor common I/O helpers into Io
 trait

On Fri Jan 16, 2026 at 10:44 AM GMT, Alice Ryhl wrote:
> On Thu, Jan 15, 2026 at 11:26:46PM +0200, Zhi Wang wrote:
>> The previous Io<SIZE> type combined both the generic I/O access helpers
>> and MMIO implementation details in a single struct.
>> 
>> To establish a cleaner layering between the I/O interface and its concrete
>> backends, paving the way for supporting additional I/O mechanisms in the
>> future, Io<SIZE> need to be factored.
>> 
>> Factor the common helpers into new {Io, Io64} traits, and move the
>> MMIO-specific logic into a dedicated Mmio<SIZE> type implementing that
>> trait. Rename the IoRaw to MmioRaw and update the bus MMIO implementations
>> to use MmioRaw.
>> 
>> No functional change intended.
>> 
>> Cc: Alexandre Courbot <acourbot@...dia.com>
>> Cc: Alice Ryhl <aliceryhl@...gle.com>
>> Cc: Bjorn Helgaas <helgaas@...nel.org>
>> Cc: Danilo Krummrich <dakr@...nel.org>
>> Cc: John Hubbard <jhubbard@...dia.com>
>> Signed-off-by: Zhi Wang <zhiw@...dia.com>
>
>> +pub trait IoBase {
>> +pub trait IoKnownSize: IoBase {
>> +pub trait Io: IoBase {
>> +pub trait IoKnownSize64: IoKnownSize {
>> +pub trait Io64: Io {
>
> The following combinations are possible:
>
> 1. IoBase
> 2. IoBase + Io
> 3. IoBase + IoKnownSize
> 4. IoBase + Io + IoKnownSize
> 5. IoBase + Io + Io64
> 6. IoBase + Io + Io64 + IoKnownSize
> 7. IoBase + IoKnownSize + IoKnownSize64
> 8. IoBase + Io + IoKnownSize + IoKnownSize64
> 9. IoBase + Io + IoKnownSize + Io64 + IoKnownSize64
>
> I'm not sure all of them make sense. I can't see a scenario where I
> would pick 1, 3, 6, 7, or 8.
>
> How about this trait hierachy? I believe I suggested something along
> these lines before.
>
> pub trait Io {
> pub trait Io64: Io {
> pub trait IoKnownSize: Io {
>
> With these traits, these scenarios are possible:
>
> 1. Io
> 2. Io + Io64
> 3. Io + IoKnownSize
> 4. Io + Io64 + IoKnownSize
>
> which seems to be the actual set of cases we care about.
>
> Note that IoKnownSize can have methods that only apply when Io64 is
> implemented:
>
> trait IoKnownSize: Io {
>     /// Infallible 8-bit read with compile-time bounds check.
>     fn read8(&self, offset: usize) -> u8;
>
>     /// Infallible 64-bit read with compile-time bounds check.
>     fn read64(&self, offset: usize) -> u64
>     where
>     	Self: Io64;
> }

I like this.

I wonder if we can keep all methods on `Io` trait. And then have marker trait to
represent capability on performing Io access.

Something like:

trait IoCapable<T> {}

trait Io {
     fn read8(&self, offset: usize) -> u8 where Self: IoCapable<u8>;
     fn read16(&self, offset: usize) -> u16 where Self: IoCapable<u16>;
     fn read32(&self, offset: usize) -> u32 where Self: IoCapable<u32>;
     fn read64(&self, offset: usize) -> u64 where Self: IoCapable<u64>;
}

Then you have a single (non-marker) trait and not a hierachy of them.

Best,
Gary