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Message-ID: <3bad6983-b412-4386-931c-4eca3ed54da3@kernel.org>
Date: Mon, 20 Oct 2025 16:18:26 +0200
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Subject: Re: [PATCH 1/2] rust: bitmap: add MAX_LEN and NO_ALLOC_MAX_LEN
 constants
To: Alice Ryhl <aliceryhl@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
 Yury Norov <yury.norov@gmail.com>, =?UTF-8?Q?Arve_Hj=C3=B8nnev=C3=A5g?=
 <arve@android.com>, Todd Kjos <tkjos@android.com>,
 Martijn Coenen <maco@android.com>, Joel Fernandes <joelagnelf@nvidia.com>,
 Christian Brauner <brauner@kernel.org>, Carlos Llamas <cmllamas@google.com>,
 Suren Baghdasaryan <surenb@google.com>, Burak Emir <bqe@google.com>,
 Miguel Ojeda <ojeda@kernel.org>, Boqun Feng <boqun.feng@gmail.com>,
 Gary Guo <gary@garyguo.net>, =?UTF-8?Q?Bj=C3=B6rn_Roy_Baron?=
 <bjorn3_gh@protonmail.com>, Benno Lossin <lossin@kernel.org>,
 Andreas Hindborg <a.hindborg@kernel.org>, Trevor Gross <tmgross@umich.edu>,
 rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20251020-binder-bitmap-v1-0-879bec9cddc1@google.com>
 <20251020-binder-bitmap-v1-1-879bec9cddc1@google.com>
From: Danilo Krummrich <dakr@kernel.org>
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In-Reply-To: <20251020-binder-bitmap-v1-1-879bec9cddc1@google.com>
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On 10/20/25 3:33 PM, Alice Ryhl wrote:
> To avoid hard-coding these values in drivers, define constants for them
> that drivers can reference.
> 
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>

Yes, please! :)

Acked-by: Danilo Krummrich <dakr@kernel.org>

> @@ -238,11 +244,11 @@ pub fn new(nbits: usize, flags: Flags) -> Result<Self, AllocError> {
>                  nbits,
>              });
>          }
> -        if nbits > i32::MAX.try_into().unwrap() {
> +        if nbits > Self::MAX_LEN {
>              return Err(AllocError);
>          }
>          let nbits_u32 = u32::try_from(nbits).unwrap();

Can we also get rid of this please? :)

> -        // SAFETY: `BITS_PER_LONG < nbits` and `nbits <= i32::MAX`.
> +        // SAFETY: `BITS_PER_LONG < nbits` and `nbits <= MAX_LEN`.
>          let ptr = unsafe { bindings::bitmap_zalloc(nbits_u32, flags.as_raw()) };
>          let ptr = NonNull::new(ptr).ok_or(AllocError)?;
>          // INVARIANT: `ptr` returned by C `bitmap_zalloc` and `nbits` checked.