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

[Hannes Reinecke <hare@suse.de>]

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@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)
> 
Can't we overload .contains() to check only power-of-2 values?

Cheers,

Hannes