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

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Date: Thu, 14 Mar 2024 09:58:23 +0100
From: Andreas Hindborg <nmi@...aspace.dk>
To: Boqun Feng <boqun.feng@...il.com>
Cc: Jens Axboe <axboe@...nel.dk>,  Christoph Hellwig <hch@....de>,  Keith
 Busch <kbusch@...nel.org>, 	Damien Le Moal <Damien.LeMoal@....com>,  Bart
 Van Assche <bvanassche@....org>, 	Hannes Reinecke <hare@...e.de>,
  "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,  Andreas
 Hindborg <a.hindborg@...sung.com>,  Wedson Almeida Filho
 <wedsonaf@...il.com>,  Niklas Cassel <Niklas.Cassel@....com>,  Greg KH
 <gregkh@...uxfoundation.org>,  Matthew Wilcox <willy@...radead.org>,
 	Miguel Ojeda <ojeda@...nel.org>,  Alex Gaynor <alex.gaynor@...il.com>,
  Gary Guo <gary@...yguo.net>,  Björn Roy Baron
 <bjorn3_gh@...tonmail.com>,
  Benno Lossin <benno.lossin@...ton.me>, 	Alice Ryhl
 <aliceryhl@...gle.com>,  Chaitanya Kulkarni <chaitanyak@...dia.com>,  Luis
 Chamberlain <mcgrof@...nel.org>,  Yexuan Yang <1182282462@...t.edu.cn>,
  Sergio González Collado <sergio.collado@...il.com>,  Joel
 Granados
 <j.granados@...sung.com>,  "Pankaj Raghav (Samsung)"
 <kernel@...kajraghav.com>,  Daniel Gomez <da.gomez@...sung.com>,  open
 list <linux-kernel@...r.kernel.org>,  "rust-for-linux@...r.kernel.org"
 <rust-for-linux@...r.kernel.org>,  "lsf-pc@...ts.linux-foundation.org"
 <lsf-pc@...ts.linux-foundation.org>,  "gost.dev@...sung.com"
 <gost.dev@...sung.com>
Subject: Re: [RFC PATCH 1/5] rust: block: introduce `kernel::block::mq` module

Boqun Feng <boqun.feng@...il.com> writes:

> On Wed, Mar 13, 2024 at 12:05:08PM +0100, Andreas Hindborg wrote:
>> From: Andreas Hindborg <a.hindborg@...sung.com>
>> 
>> Add initial abstractions for working with blk-mq.
>> 
>> This patch is a maintained, refactored subset of code originally published by
>> Wedson Almeida Filho <wedsonaf@...il.com> [1].
>> 
>> [1] https://github.com/wedsonaf/linux/tree/f2cfd2fe0e2ca4e90994f96afe268bbd4382a891/rust/kernel/blk/mq.rs
>> 
>> Cc: Wedson Almeida Filho <wedsonaf@...il.com>
>> Signed-off-by: Andreas Hindborg <a.hindborg@...sung.com>
>> ---
>>  block/blk-mq.c                     |   3 +-
>>  include/linux/blk-mq.h             |   1 +
>>  rust/bindings/bindings_helper.h    |   2 +
>>  rust/helpers.c                     |  45 ++++
>>  rust/kernel/block.rs               |   5 +
>>  rust/kernel/block/mq.rs            | 131 +++++++++++
>>  rust/kernel/block/mq/gen_disk.rs   | 174 +++++++++++++++
>>  rust/kernel/block/mq/operations.rs | 346 +++++++++++++++++++++++++++++
>>  rust/kernel/block/mq/raw_writer.rs |  60 +++++
>>  rust/kernel/block/mq/request.rs    | 182 +++++++++++++++
>>  rust/kernel/block/mq/tag_set.rs    | 117 ++++++++++
>>  rust/kernel/error.rs               |   5 +
>>  rust/kernel/lib.rs                 |   1 +
>>  13 files changed, 1071 insertions(+), 1 deletion(-)
>>  create mode 100644 rust/kernel/block.rs
>>  create mode 100644 rust/kernel/block/mq.rs
>>  create mode 100644 rust/kernel/block/mq/gen_disk.rs
>>  create mode 100644 rust/kernel/block/mq/operations.rs
>>  create mode 100644 rust/kernel/block/mq/raw_writer.rs
>>  create mode 100644 rust/kernel/block/mq/request.rs
>>  create mode 100644 rust/kernel/block/mq/tag_set.rs
>> 
>> diff --git a/block/blk-mq.c b/block/blk-mq.c
>> index 2dc01551e27c..a531f664bee7 100644
>> --- a/block/blk-mq.c
>> +++ b/block/blk-mq.c
>> @@ -702,7 +702,7 @@ static void blk_mq_finish_request(struct request *rq)
>>  	}
>>  }
>>  
>> -static void __blk_mq_free_request(struct request *rq)
>> +void __blk_mq_free_request(struct request *rq)
>>  {
>>  	struct request_queue *q = rq->q;
>>  	struct blk_mq_ctx *ctx = rq->mq_ctx;
>> @@ -722,6 +722,7 @@ static void __blk_mq_free_request(struct request *rq)
>>  	blk_mq_sched_restart(hctx);
>>  	blk_queue_exit(q);
>>  }
>> +EXPORT_SYMBOL_GPL(__blk_mq_free_request);
>>  
>
> Note that for an EXPORT_SYMBOL_GPL() symbol, you can just add the
> corresponding header file in rust/bindings/bindings_helper.h:
>
> +#include <linux/blk-mq.h>
>
> and you will be able to call it from Rust via:
>
> 	bindings::__blk_mq_free_request()
>
> in other words, rust_helper_blk_mq_free_request_internal() is probably
> not necessary.

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.

BR Andreas