linux-kernel - Re: [PATCH v3 2/3] rust: block: add rnull, Rust null

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Message-ID: <87ed9goqvp.fsf@metaspace.dk>
Date: Sat, 01 Jun 2024 13:15:54 +0200
From: Andreas Hindborg <nmi@...aspace.dk>
To: Benno Lossin <benno.lossin@...ton.me>
Cc: Jens Axboe <axboe@...nel.dk>,  Christoph Hellwig <hch@....de>,  Keith
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Subject: Re: [PATCH v3 2/3] rust: block: add rnull, Rust null_blk
 implementation

Benno Lossin <benno.lossin@...ton.me> writes:

>> +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);
>> +            }
>> +
>> +            let mut disk = gen_disk::GenDisk::try_new(tagset)?;
>> +            disk.set_name(format_args!("rnullb{}", 0))?;
>> +            disk.set_capacity_sectors(4096 << 11);
>> +            disk.set_queue_logical_block_size(block_size.into());
>> +            disk.set_queue_physical_block_size(block_size.into());
>> +            disk.set_rotational(false);
>> +            disk.add()
>> +        }?;
>
> Personally, I would prefer to put the `?` into the line above.

I have no strong opinion here.

>
>> +
>> +        let disk = Box::pin_init(new_mutex!(disk, "nullb:disk"), flags::GFP_KERNEL)?;
>> +
>> +        Ok(Self { _disk: disk })
>> +    }
>> +}
>> +
>> +struct NullBlkDevice;
>> +
>> +#[vtable]
>> +impl Operations for NullBlkDevice {
>> +    #[inline(always)]
>> +    fn queue_rq(rq: ARef<mq::Request<Self>>, _is_last: bool) -> Result {
>> +        mq::Request::end_ok(rq)
>> +            .map_err(|_e| kernel::error::code::EIO)
>> +            .expect("Fatal error - expected to be able to end request");
>
> I expected something more along the lines of: "expected to be able to
> end request, since `NullBlkDevice` never takes refcounts on Requests and
> as such the ARef must be unique, but `end_ok` only fails if that is not
> the case". But maybe that would fit better in a comment, what do you
> think?

I can add a comment 👍

BR Andreas