Re: [PATCH v4 2/3] rust: block: add rnull, Rust null_blk implementation

[Hannes Reinecke]

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@xxxxxxxxxx> 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