linux-kernel - Re: [PATCH v4 2/3] rust: block: add rnull, Rust null

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Message-ID: <87sexvn17o.fsf@metaspace.dk>
Date: Sun, 02 Jun 2024 11:27:55 +0200
From: Andreas Hindborg <nmi@...aspace.dk>
To: Matthew Wilcox <willy@...radead.org>
Cc: Keith Busch <kbusch@...nel.org>,  Jens Axboe <axboe@...nel.dk>,
  Christoph Hellwig <hch@....de>,  Damien Le Moal <dlemoal@...nel.org>,
  Bart Van Assche <bvanassche@....org>,  Hannes Reinecke <hare@...e.de>,
  Ming Lei <ming.lei@...hat.com>,  "linux-block@...r.kernel.org"
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Subject: Re: [PATCH v4 2/3] rust: block: add rnull, Rust null_blk
 implementation

Matthew Wilcox <willy@...radead.org> writes:

> On Sat, Jun 01, 2024 at 10:01:40AM -0600, Keith Busch wrote:
>> 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)
>
> I'd drop the range check.  We're pretty close to landing the bs>PS
> patches, so just
>
> 	if block_size & block_size - 1 != 0
>
> should be enough of a validation.

Is it safe to do so already? Otherwise we just remove it when it is
safe, no biggie.

> Is it considered "good style" in
> Rust to omit the brackets here?

Yes, the compiler will complain if you add parenthesis here.

```rust
fn main() {
    if (true) {
        return;
    }
}
```

Building this will give you:

```text
warning: unnecessary parentheses around `if` condition
 --> src/main.rs:2:8
  |
2 |     if (true) {
  |        ^    ^
  |
  = note: `#[warn(unused_parens)]` on by default
help: remove these parentheses
  |
2 -     if (true) {
2 +     if true {
  |

warning: `playground` (bin "playground") generated 1 warning (run `cargo fix --bin "playground"` to apply 1 suggestion)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.64s
     Running `target/debug/playground`
```

If you omit the `{}` block after the `if` it is a syntax error.

Best regards,
Andreas