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

Ming Lei
2024-03-15T12:18:09Z

On Fri, Mar 15, 2024 at 08:52:46AM +0100, Andreas Hindborg wrote:
> Miguel Ojeda <miguel.ojeda.sandonis@gmail.com> writes:
>
> > On Thu, Mar 14, 2024 at 8:23 PM Andreas Hindborg <nmi@metaspace.dk> wrote:
> >>
> >> 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?
> >
> > Yeah, something needs to be exported since there is a generic
> > involved, but even if you want to go the route of exporting only a
> > different symbol, you would still want to put it in the C header so
> > that you don't get the C missing declaration warning and so that we
> > don't have to write the declaration manually in the helper.
>
> That is what I did:
>
> @@ -703,6 +703,7 @@ int blk_mq_alloc_sq_tag_set(struct blk_mq_tag_set *set,
> unsigned int set_flags);
> void blk_mq_free_tag_set(struct blk_mq_tag_set *set);
>
> +void __blk_mq_free_request(struct request *rq);
> void blk_mq_free_request(struct request *rq);
> int blk_rq_poll(struct request *rq, struct io_comp_batch *iob,
> unsigned int poll_flags);

Can you explain in detail why one block layer internal helper is
called into rnull driver directly? It never happens in C driver code.

Thanks,
Ming