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

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Message-ID: <ZltF5NvDnKFphcOo@kbusch-mbp.dhcp.thefacebook.com>
Date: Sat, 1 Jun 2024 10:01:40 -0600
From: Keith Busch <kbusch@...nel.org>
To: Andreas Hindborg <nmi@...aspace.dk>
Cc: Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>,
	Damien Le Moal <dlemoal@...nel.org>,
	Bart Van Assche <bvanassche@....org>,
	Hannes Reinecke <hare@...e.de>, 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>,
	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>,
	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 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)