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[73.105.0.253]) by smtp.gmail.com with ESMTPSA id 956f58d0204a3-640da6324f5sm2159170d50.27.2025.11.10.07.01.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 10 Nov 2025 07:01:30 -0800 (PST) Date: Mon, 10 Nov 2025 10:01:29 -0500 From: Yury Norov To: Alice Ryhl Cc: Tamir Duberstein , Greg Kroah-Hartman , Arve =?iso-8859-1?B?SGr4bm5lduVn?= , Todd Kjos , Martijn Coenen , Joel Fernandes , Christian Brauner , Carlos Llamas , Suren Baghdasaryan , Burak Emir , Miguel Ojeda , Boqun Feng , Gary Guo , =?iso-8859-1?Q?Bj=F6rn?= Roy Baron , Benno Lossin , Andreas Hindborg , Trevor Gross , Danilo Krummrich , rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 1/6] rust: bitmap: add MAX_LEN and NO_ALLOC_MAX_LEN constants Message-ID: References: <20251110-binder-bitmap-v4-0-5ed8a7fab1b9@google.com> <20251110-binder-bitmap-v4-1-5ed8a7fab1b9@google.com> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Mon, Nov 10, 2025 at 02:20:17PM +0000, Alice Ryhl wrote: > On Mon, Nov 10, 2025 at 08:59:36AM -0500, Tamir Duberstein wrote: > > On Mon, Nov 10, 2025 at 8:06 AM Alice Ryhl wrote: > > > > > > To avoid hard-coding these values in drivers, define constants for them > > > that drivers can reference. > > > > > > Acked-by: Danilo Krummrich > > > Reviewed-by: Burak Emir > > > Signed-off-by: Alice Ryhl > > > --- > > > rust/kernel/bitmap.rs | 16 +++++++++++----- > > > 1 file changed, 11 insertions(+), 5 deletions(-) > > > > > > diff --git a/rust/kernel/bitmap.rs b/rust/kernel/bitmap.rs > > > index aa8fc7bf06fc99865ae755d8694e4bec3dc8e7f0..15fa23b45054b9272415fcc000e3e3b52c74d7c1 100644 > > > --- a/rust/kernel/bitmap.rs > > > +++ b/rust/kernel/bitmap.rs > > > @@ -149,14 +149,14 @@ macro_rules! bitmap_assert_return { > > > /// > > > /// # Invariants > > > /// > > > -/// * `nbits` is `<= i32::MAX` and never changes. > > > +/// * `nbits` is `<= MAX_LEN`. > > > /// * if `nbits <= bindings::BITS_PER_LONG`, then `repr` is a `usize`. > > > > Should this and other references to bindings::BITS_PER_LONG be > > `NO_ALLOC_MAX_LEN` instead? > > Ah yeah it probably makes sense to update this in a bunch of places. Yes, please. NO_ALLOC sounds a bit weird in exported API. Maybe NBITS_INPLACE or similar? Also, at this point we're really close to: pub const NBITS_INPLACE: usize = CONFIG_NBITS_INPLACE; union BitmapRepr { bitmap: [usize, BITS_TO_LONGS(NBITS_INPLACE)] ptr: NonNull, } That would be a very useful addition for some particular scenarios, I believe. Even if you don't want to make it configurable, let's keep this option in mind? Thanks, Yury