Re: [RFC PATCH 1/5] rust: block: introduce `kernel::block::mq` module

[Andreas Hindborg]

Andreas Hindborg <nmi@xxxxxxxxxxxx> writes:

> Miguel Ojeda <miguel.ojeda.sandonis@xxxxxxxxx> writes:
>
>> On Thu, Mar 14, 2024 at 9:58 AM Andreas Hindborg <nmi@xxxxxxxxxxxx> wrote:
>>>
>>> Yes, good point. Another option suggested by Miguel is that
>>> `__blk_mq_free_request` need not be exported at all. We can make it
>>> non-static and then call it from
>>> `rust_helper_blk_mq_free_request_internal()`. Then only the latter will
>>> be in the kernel image symbol table, which might be better in terms of
>>> not exposing `__blk_mq_free_request()` directly.
>>
>> The helper is not needed, i.e. what I meant was to make it non-static
>> and add it to `include/linux/blk-mq.h`.
>
> The way the current code compiles, <kernel::block::mq::Request as
> kernel::types::AlwaysRefCounted>::dec_ref` is inlined into the `rnull`
> module. A relocation for `rust_helper_blk_mq_free_request_internal`
> appears in `rnull_mod.ko`. I didn't test it yet, but if
> `__blk_mq_free_request` (or the helper) is not exported, I don't think
> this would be possible?
>

I just tested what you suggested Miguel, and I get a link error for
`__blk_mq_free_request` being undefined when the module is linked. This
is even though the code that calls this function lives in the `kernel`
crate, because it is inlined.

BR Andreas