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

Keith Busch
2024-06-01T16:01:44Z

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)