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Date: Sat, 1 Jun 2024 10:01:40 -0600
From: Keith Busch <kbusch@kernel.org>
To: Andreas Hindborg <nmi@metaspace.dk>
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Subject: Re: [PATCH v4 2/3] rust: block: add rnull, Rust null_blk
 implementation
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On Sat, Jun 01, 2024 at 05:36:20PM +0200, Andreas Hindborg wrote:
> Keith Busch <kbusch@kernel.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)