Received-SPF: pass (google.com: domain of linux-kernel+bounces-103734-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.199.223 as permitted sender) client-ip=147.75.199.223;
From: Andreas Hindborg <nmi@metaspace.dk>
To: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Cc: Boqun Feng <boqun.feng@gmail.com>,  Jens Axboe <axboe@kernel.dk>,
  Christoph Hellwig <hch@lst.de>,  Keith Busch <kbusch@kernel.org>,  Damien
 Le Moal <Damien.LeMoal@wdc.com>,  Bart Van Assche <bvanassche@acm.org>,
  Hannes Reinecke <hare@suse.de>,  "linux-block@vger.kernel.org"
 <linux-block@vger.kernel.org>,  Andreas Hindborg <a.hindborg@samsung.com>,
  Wedson Almeida Filho <wedsonaf@gmail.com>,  Niklas Cassel
 <Niklas.Cassel@wdc.com>,  Greg KH <gregkh@linuxfoundation.org>,  Matthew
 Wilcox <willy@infradead.org>,  Miguel Ojeda <ojeda@kernel.org>,  Alex
 Gaynor <alex.gaynor@gmail.com>,  Gary Guo <gary@garyguo.net>,
  =?utf-8?Q?Bj=C3=B6rn?= Roy
 Baron <bjorn3_gh@protonmail.com>,  Benno Lossin <benno.lossin@proton.me>,
  Alice Ryhl <aliceryhl@google.com>,  Chaitanya Kulkarni
 <chaitanyak@nvidia.com>,  Luis Chamberlain <mcgrof@kernel.org>,  Yexuan
 Yang <1182282462@bupt.edu.cn>,  Sergio =?utf-8?Q?Gonz=C3=A1lez?= Collado
 <sergio.collado@gmail.com>,  Joel Granados <j.granados@samsung.com>,
  "Pankaj Raghav (Samsung)" <kernel@pankajraghav.com>,  Daniel Gomez
 <da.gomez@samsung.com>,  open list <linux-kernel@vger.kernel.org>,
  "rust-for-linux@vger.kernel.org" <rust-for-linux@vger.kernel.org>,
  "lsf-pc@lists.linux-foundation.org" <lsf-pc@lists.linux-foundation.org>,
  "gost.dev@samsung.com" <gost.dev@samsung.com>
Subject: Re: [RFC PATCH 1/5] rust: block: introduce `kernel::block::mq` module
In-Reply-To: <87plvwsjn5.fsf@metaspace.dk> (Andreas Hindborg's message of
	"Thu, 14 Mar 2024 20:22:54 +0100")
References: <20240313110515.70088-1-nmi@metaspace.dk>
	<20240313110515.70088-2-nmi@metaspace.dk> <ZfI8-14RUqGqoRd-@boqun-archlinux>
	<87il1ptck0.fsf@metaspace.dk>
	<CANiq72mzBe2npLo=CVR=ShyMuDmr0+TW4Gy0coPFQOBQZ_VnwQ@mail.gmail.com>
	<87plvwsjn5.fsf@metaspace.dk>
User-Agent: mu4e 1.12.0; emacs 29.2
Date: Thu, 14 Mar 2024 20:41:10 +0100
Message-ID: <87h6h8sisp.fsf@metaspace.dk>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable

Andreas Hindborg <nmi@metaspace.dk> writes:

> Miguel Ojeda <miguel.ojeda.sandonis@gmail.com> writes:
>
>> On Thu, Mar 14, 2024 at 9:58=E2=80=AFAM Andreas Hindborg <nmi@metaspace.=
dk> 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