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Date: Wed, 11 Mar 2026 17:22:19 +0100
Message-Id: <DH03AMF92KPJ.34AJPXRVWF2Q5@kernel.org>
Subject: Re: [PATCH v8 07/10] rust: io: introduce `IntoIoVal` trait and
 single-argument `write_val`
Cc: "Alexandre Courbot" <acourbot@nvidia.com>, "Alice Ryhl"
 <aliceryhl@google.com>, "Daniel Almeida" <daniel.almeida@collabora.com>,
 "Miguel Ojeda" <ojeda@kernel.org>, =?utf-8?q?Bj=C3=B6rn_Roy_Baron?=
 <bjorn3_gh@protonmail.com>, "Benno Lossin" <lossin@kernel.org>, "Andreas
 Hindborg" <a.hindborg@kernel.org>, "Trevor Gross" <tmgross@umich.edu>,
 "Boqun Feng" <boqun@kernel.org>, "Yury Norov" <yury.norov@gmail.com>, "John
 Hubbard" <jhubbard@nvidia.com>, "Alistair Popple" <apopple@nvidia.com>,
 "Joel Fernandes" <joelagnelf@nvidia.com>, "Timur Tabi" <ttabi@nvidia.com>,
 "Edwin Peer" <epeer@nvidia.com>, "Eliot Courtney" <ecourtney@nvidia.com>,
 "Dirk Behme" <dirk.behme@de.bosch.com>, "Steven Price"
 <steven.price@arm.com>, <rust-for-linux@vger.kernel.org>,
 <linux-kernel@vger.kernel.org>
To: "Gary Guo" <gary@garyguo.net>
From: "Danilo Krummrich" <dakr@kernel.org>
References: <20260310-register-v8-0-424f80dd43bc@nvidia.com>
 <20260310-register-v8-7-424f80dd43bc@nvidia.com>
 <DGZ8XPCCUDQ5.14RUPZWK8L509@kernel.org>
 <DGZZLNFLSJ4E.2P42FMI1XT47W@nvidia.com>
 <DH01GX7X7LSY.1N6WXIPLDCSTX@kernel.org>
 <DH02G8SWF726.6XKAQ0XLYE3D@garyguo.net>
In-Reply-To: <DH02G8SWF726.6XKAQ0XLYE3D@garyguo.net>

On Wed Mar 11, 2026 at 4:42 PM CET, Gary Guo wrote:
> On Wed Mar 11, 2026 at 2:56 PM GMT, Danilo Krummrich wrote:
>>
>> 	fn write<T, L>(&self, location: L, value: T)
>> 	where
>> 	    L: IoLoc<T>,
>> 	    Self: IoKnownSize + IoCapable<L::IoType>,
>>
>> Which is the reason why L: IoLoc<T>, i.e. the relative location is on T,=
 not on
>> L.
>
> The location has nothing to do with `value`, just the type `T`.

(Cutting all the above, since it all boils down to the same thing.)

So, that's what I mean, the relative location is on type T (the value type)=
, not
on L (the location type), hence T can't just be an arbitrary primitive, no?

>> So, what you could say is
>>
>>   - read() takes an absolute location and returns something that encodes=
 a value
>>     and relative location
>>
>>   - write() takes a base location (or absolute location) and something t=
hat
>>     encodes a value and relative location
>
> Only `location` gives you the location. Value has nothing to do with loca=
tions at all. Type
> inference does the trick.

The value does have something to do with the relative location, as it comes=
 from
the value type. You can't pass an "independent" value whose type does not c=
arry
location information, can you?