Re: [PATCH net-next v6 1/6] rust: sizes: add commonly used constants

[Danilo Krummrich <dakr@kernel.org>]

On 8/21/24 1:41 AM, Greg KH wrote:
> On Tue, Aug 20, 2024 at 10:57:14PM +0000, FUJITA Tomonori wrote:
>> Add rust equivalent to include/linux/sizes.h, makes code more
>> readable.
>>
>> Reviewed-by: Alice Ryhl <aliceryhl@google.com>
>> Reviewed-by: Andrew Lunn <andrew@lunn.ch>
>> Reviewed-by: Benno Lossin <benno.lossin@proton.me>
>> Reviewed-by: Trevor Gross <tmgross@umich.edu>
>> Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
>> ---
>>   rust/kernel/lib.rs   |  1 +
>>   rust/kernel/sizes.rs | 26 ++++++++++++++++++++++++++
>>   2 files changed, 27 insertions(+)
>>   create mode 100644 rust/kernel/sizes.rs
>>
>> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
>> index 274bdc1b0a82..58ed400198bf 100644
>> --- a/rust/kernel/lib.rs
>> +++ b/rust/kernel/lib.rs
>> @@ -43,6 +43,7 @@
>>   pub mod page;
>>   pub mod prelude;
>>   pub mod print;
>> +pub mod sizes;
>>   mod static_assert;
>>   #[doc(hidden)]
>>   pub mod std_vendor;
>> diff --git a/rust/kernel/sizes.rs b/rust/kernel/sizes.rs
>> new file mode 100644
>> index 000000000000..834c343e4170
>> --- /dev/null
>> +++ b/rust/kernel/sizes.rs
>> @@ -0,0 +1,26 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +
>> +//! Commonly used sizes.
>> +//!
>> +//! C headers: [`include/linux/sizes.h`](srctree/include/linux/sizes.h).
>> +
>> +/// 0x00000400
>> +pub const SZ_1K: usize = bindings::SZ_1K as usize;
>> +/// 0x00000800
>> +pub const SZ_2K: usize = bindings::SZ_2K as usize;
>> +/// 0x00001000
>> +pub const SZ_4K: usize = bindings::SZ_4K as usize;
>> +/// 0x00002000
>> +pub const SZ_8K: usize = bindings::SZ_8K as usize;
>> +/// 0x00004000
>> +pub const SZ_16K: usize = bindings::SZ_16K as usize;
>> +/// 0x00008000
>> +pub const SZ_32K: usize = bindings::SZ_32K as usize;
>> +/// 0x00010000
>> +pub const SZ_64K: usize = bindings::SZ_64K as usize;
>> +/// 0x00020000
>> +pub const SZ_128K: usize = bindings::SZ_128K as usize;
>> +/// 0x00040000
>> +pub const SZ_256K: usize = bindings::SZ_256K as usize;
>> +/// 0x00080000
>> +pub const SZ_512K: usize = bindings::SZ_512K as usize;
> 
> Why only some of the values in sizes.h?
> 
> And why can't sizes.h be directly translated into rust code without
> having to do it "by hand" here?  We do that for other header file
> bindings, right?

Those are all generated bindings from C headers, e.g. `bindings::SZ_2K `, but
bindgen isn't guaranteed to assign the type we want (`usize` in this case), plus
for size constants having the `bindings::` prefix doesn't really add any value.

Rust could also define those without using bindings at all, but this was already
discussed in earlier versions of this series.

- Danilo

> 
> thanks,
> 
> greg k-h
>