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

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Message-ID: <0a47eebd-2aca-494d-814b-bc949b08630b@suse.de>
Date: Mon, 3 Jun 2024 11:05:19 +0200
From: Hannes Reinecke <hare@...e.de>
To: Keith Busch <kbusch@...nel.org>, 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>,
 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 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?

Cheers,

Hannes