linux-kernel - Re: [PATCH v4 2/3] rust: block: add rnull, Rust null

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Date: Mon, 3 Jun 2024 11:06:57 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Hannes Reinecke <hare@...e.de>
Cc: Keith Busch <kbusch@...nel.org>, Andreas Hindborg <nmi@...aspace.dk>, Jens Axboe <axboe@...nel.dk>, 
	Christoph Hellwig <hch@....de>, Damien Le Moal <dlemoal@...nel.org>, Bart Van Assche <bvanassche@....org>, 
	Ming Lei <ming.lei@...hat.com>, 
	"linux-block@...r.kernel.org" <linux-block@...r.kernel.org>, Andreas Hindborg <a.hindborg@...sung.com>, 
	Greg KH <gregkh@...uxfoundation.org>, Matthew Wilcox <willy@...radead.org>, 
	Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, 
	Wedson Almeida Filho <wedsonaf@...il.com>, Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, 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>, 
	Niklas Cassel <Niklas.Cassel@....com>, Philipp Stanner <pstanner@...hat.com>, 
	Conor Dooley <conor@...nel.org>, Johannes Thumshirn <Johannes.Thumshirn@....com>, 
	Matias Bjørling <m@...rling.me>, 
	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: [PATCH v4 2/3] rust: block: add rnull, Rust null_blk implementation

On Mon, Jun 3, 2024 at 11:05 AM Hannes Reinecke <hare@...e.de> wrote:
>
> On 6/1/24 18:01, Keith Busch wrote:
> > On Sat, Jun 01, 2024 at 05:36:20PM +0200, Andreas Hindborg wrote:
> >> Keith Busch <kbusch@...nel.org> writes:
> >>
> >>> On Sat, Jun 01, 2024 at 03:40:04PM +0200, Andreas Hindborg wrote:
> >>>> +impl kernel::Module for NullBlkModule {
> >>>> +    fn init(_module: &'static ThisModule) -> Result<Self> {
> >>>> +        pr_info!("Rust null_blk loaded\n");
> >>>> +        let tagset = Arc::pin_init(TagSet::try_new(1, 256, 1), flags::GFP_KERNEL)?;
> >>>> +
> >>>> +        let disk = {
> >>>> +            let block_size: u16 = 4096;
> >>>> +            if block_size % 512 != 0 || !(512..=4096).contains(&block_size) {
> >>>> +                return Err(kernel::error::code::EINVAL);
> >>>> +            }
> >>>
> >>> You've set block_size to the literal 4096, then validate its value
> >>> immediately after? Am I missing some way this could ever be invalid?
> >>
> >> Good catch. It is because I have a patch in the outbound queue that allows setting
> >> the block size via a module parameter. The module parameter patch is not
> >> upstream yet. Once I have that up, I will send the patch with the block
> >> size config.
> >>
> >> Do you think it is OK to have this redundancy? It would only be for a
> >> few cycles.
> >
> > It's fine, just wondering why it's there. But it also allows values like
> > 1536 and 3584, which are not valid block sizes, so I think you want the
> > check to be:
> >
> >       if !(512..=4096).contains(&block_size) || ((block_size & (block_size - 1)) != 0)
> >
> Can't we overload .contains() to check only power-of-2 values?

Rust integers have a method called is_power_of_two. If you need to
assert that it's a power of two, you can use that.

Alice