linux-kernel - Re: [PATCH] rust: add this

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Date:   Tue, 31 Jan 2023 12:07:45 -0300
From:   Martin Rodriguez Reboredo <yakoyoku@...il.com>
To:     gregkh@...uxfoundation.org
Cc:     alex.gaynor@...il.com, bjorn3_gh@...tonmail.com,
        boqun.feng@...il.com, gary@...yguo.net,
        linux-kernel@...r.kernel.org, ojeda@...nel.org,
        rust-for-linux@...r.kernel.org, wedsonaf@...il.com,
        yakoyoku@...il.com
Subject: Re: [PATCH] rust: add this_module macro

On Tue, Jan 31, 2023 at 02:42:08PM +0100, Greg KH wrote:
>On Tue, Jan 31, 2023 at 10:08:41AM -0300, Martin Rodriguez Reboredo wrote:
>> Adds a Rust equivalent to the handy THIS_MODULE macro from C.
>> 
>> Signed-off-by: Martin Rodriguez Reboredo <yakoyoku@...il.com>
>> ---
>>  rust/kernel/lib.rs | 12 ++++++++++++
>>  1 file changed, 12 insertions(+)
>> 
>> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
>> index e0b0e953907d..afb6b0390426 100644
>> --- a/rust/kernel/lib.rs
>> +++ b/rust/kernel/lib.rs
>> @@ -80,6 +80,18 @@ impl ThisModule {
>>      }
>>  }
>>  
>> +/// Returns the current module.
>> +#[macro_export]
>> +macro_rules! this_module {
>> +    () => {
>> +        if cfg!(MODULE) {
>> +            Some(unsafe { $crate::ThisModule::from_ptr(&mut $crate::bindings::__this_module) })
>> +        } else {
>> +            None
>> +        }
>> +    };
>> +}
>
>While this is handy, what exactly will it be used for?  The C
>wrappers/shim/whatever should probably handle this for you already when
>you save this pointer into a structure right?
>
>Surely you aren't trying to increment your own module's reference count,
>right?  That just doesn't work :)
>
>thanks,
>
>greg k-h

This was meant for setting the owner field of a file_operations struct
or the cra_owner field of crypto_alg and many other structs.

I know that increfing a module without a good reason is dead dumb, so
I'm not trying to send things in a downwards spiral. @@@

And yes, I should have mentioned that in the commit message, but I let
slip that detail.