Re: [PATCH] rust: impl_flags: add method to return underlying integer

[Gary Guo <gary@garyguo.net>]

On 2026-02-14 08:02, Andreas Hindborg wrote:
> Gary Guo <gary@garyguo.net> writes:
> 
>> On 2026-02-12 16:02, Andreas Hindborg wrote:
>>> Add a method to return the underlying integer used for flags. This is
>>> useful when using the flags with C APIs.
>>> 
>>> Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
>>
>> I am not sure if we want to actually expose the underlying representation
>> for all flags. It should be something up to the caller of `impl_flags` to
>> decide.
>>
>> Would it make sense to add visibility the wrapped raw type so that you
>> can do
>>
>> impl_flags! {
>>     pub struct Foo(pub u32);
>>     ...
>> }
>>
>> to make the inner accessible?
> 
> I don't see how that is better?
> 
>                 bindings::blk_mq_tag_set {
>                     ...
>                     flags: flags.into_inner(),
>                     ...
>                 }
> 
> vs
> 
>                 bindings::blk_mq_tag_set {
>                     ...
>                     flags: flags.0,
>                     ...
>                 }
> 
> 
> I would prefer the first one.

How about we expand `($inner_vis:vis $ty:ty)` to be

    $inner_vis fn into_inner(self) -> $ty {}

? This way unless you explicitly put `pub` there, users outside the module
cannot query the bit pattern.

> 
> We are going to need to be able to pass these flags into C APIs. I feel
> like adding a method to do this is the best way to go about this. We can
> call it something else if that communicates the purpose better.

I think `bitflags` crate call this `bits`, which I think is indeed
slightly better than `into_inner`.

Best,
Gary

> 
> Best regards,
> Andreas Hindborg