Re: [RFC PATCH 00/11] Rust null block driver

From: Jens Axboe <axboe@kernel.dk>
To: Keith Busch <kbusch@kernel.org>, Bart Van Assche <bvanassche@acm.org>
Cc: "Andreas Hindborg" <nmi@metaspace.dk>,
	"Christoph Hellwig" <hch@lst.de>,
	"Damien Le Moal" <Damien.LeMoal@wdc.com>,
	"Hannes Reinecke" <hare@suse.de>,
	lsf-pc@lists.linux-foundation.org,
	rust-for-linux@vger.kernel.org, linux-block@vger.kernel.org,
	"Matthew Wilcox" <willy@infradead.org>,
	"Miguel Ojeda" <ojeda@kernel.org>,
	"Alex Gaynor" <alex.gaynor@gmail.com>,
	"Wedson Almeida Filho" <wedsonaf@gmail.com>,
	"Boqun Feng" <boqun.feng@gmail.com>,
	"Gary Guo" <gary@garyguo.net>,
	"Björn Roy Baron" <bjorn3_gh@protonmail.com>,
	"Benno Lossin" <benno.lossin@proton.me>,
	"open list" <linux-kernel@vger.kernel.org>,
	gost.dev@samsung.com
Subject: Re: [RFC PATCH 00/11] Rust null block driver
Date: Thu, 4 May 2023 13:02:19 -0600	[thread overview]
Message-ID: <e7bc2155-613b-8904-9942-2e9615b0dc63@kernel.dk> (raw)
In-Reply-To: <ZFP+8apHunCCMmOZ@kbusch-mbp.dhcp.thefacebook.com>

On 5/4/23 12:52?PM, Keith Busch wrote:
> On Thu, May 04, 2023 at 11:36:01AM -0700, Bart Van Assche wrote:
>> On 5/4/23 11:15, Andreas Hindborg wrote:
>>> If it is still unclear to you why this effort was started, please do let
>>> me know and I shall try to clarify further :)
>>
>> It seems like I was too polite in my previous email. What I meant is that
>> rewriting code is useful if it provides a clear advantage to the users of
>> a driver. For null_blk, the users are kernel developers. The code that has
>> been posted is the start of a rewrite of the null_blk driver. The benefits
>> of this rewrite (making low-level memory errors less likely) do not outweigh
>> the risks that this effort will introduce functional or performance regressions.
> 
> Instead of replacing, would co-existing be okay? Of course as long as
> there's no requirement to maintain feature parity between the two.
> Actually, just call it "rust_blk" and declare it has no relationship to
> null_blk, despite their functional similarities: it's a developer
> reference implementation for a rust block driver.

To me, the big discussion point isn't really whether we're doing
null_blk or not, it's more if we want to go down this path of
maintaining rust bindings for the block code in general. If the answer
to that is yes, then doing null_blk seems like a great choice as it's
not a critical piece of infrastructure. It might even be a good idea to
be able to run both, for performance purposes, as the bindings or core
changes.

But back to the real question... This is obviously extra burden on
maintainers, and that needs to be sorted out first. Block drivers in
general are not super security sensitive, as it's mostly privileged code
and there's not a whole lot of user visibile API. And the stuff we do
have is reasonably basic. So what's the long term win of having rust
bindings? This is a legitimate question. I can see a lot of other more
user exposed subsystems being of higher interest here.

-- 
Jens Axboe