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From: Alice Ryhl <aliceryhl@google.com>
Date: Mon, 3 Jun 2024 11:06:57 +0200
Message-ID: <CAH5fLgiSCTa=BCr2aGZBhsY2gvctE9OTFFA5CNiVR-YGbXhgxg@mail.gmail.com>
Subject: Re: [PATCH v4 2/3] rust: block: add rnull, Rust null_blk implementation
To: Hannes Reinecke <hare@suse.de>
Cc: Keith Busch <kbusch@kernel.org>, Andreas Hindborg <nmi@metaspace.dk>, Jens Axboe <axboe@kernel.dk>, 
	Christoph Hellwig <hch@lst.de>, Damien Le Moal <dlemoal@kernel.org>, Bart Van Assche <bvanassche@acm.org>, 
	Ming Lei <ming.lei@redhat.com>, 
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>, Andreas Hindborg <a.hindborg@samsung.com>, 
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	Miguel Ojeda <ojeda@kernel.org>, Alex Gaynor <alex.gaynor@gmail.com>, 
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	=?UTF-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>, 
	Benno Lossin <benno.lossin@proton.me>, Chaitanya Kulkarni <chaitanyak@nvidia.com>, 
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On Mon, Jun 3, 2024 at 11:05=E2=80=AFAM Hannes Reinecke <hare@suse.de> wrot=
e:
>
> 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 =3D Arc::pin_init(TagSet::try_new(1, 256, 1), fl=
ags::GFP_KERNEL)?;
> >>>> +
> >>>> +        let disk =3D {
> >>>> +            let block_size: u16 =3D 4096;
> >>>> +            if block_size % 512 !=3D 0 || !(512..=3D4096).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 al=
lows setting
> >> the block size via a module parameter. The module parameter patch is n=
ot
> >> upstream yet. Once I have that up, I will send the patch with the bloc=
k
> >> 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 lik=
e
> > 1536 and 3584, which are not valid block sizes, so I think you want the
> > check to be:
> >
> >       if !(512..=3D4096).contains(&block_size) || ((block_size & (block=
_size - 1)) !=3D 0)
> >
> Can't we overload .contains() to check only power-of-2 values?

Rust integers have a method called is_power_of_two. If you need to
assert that it's a power of two, you can use that.

Alice